memjournal.lo \
        mutex.lo mutex_noop.lo mutex_os2.lo mutex_unix.lo mutex_w32.lo \
        notify.lo opcodes.lo os.lo os_unix.lo os_win.lo os_os2.lo \
        pager.lo parse.lo pcache.lo pcache1.lo pragma.lo prepare.lo printf.lo \
        random.lo resolve.lo rowset.lo select.lo status.lo \
        table.lo tokenize.lo trigger.lo update.lo \
        util.lo vacuum.lo \
        vdbe.lo vdbeapi.lo vdbeaux.lo vdbeblob.lo vdbemem.lo \
        walker.lo where.lo utf.lo vtab.lo

# Object files for the amalgamation.
#
OBJS1 = sqlite3.lo

# Determine the real value of LIBOBJ based on the 'configure' script
................................................................................
  $(TOP)/src/vacuum.c \
  $(TOP)/src/vdbe.c \
  $(TOP)/src/vdbe.h \
  $(TOP)/src/vdbeapi.c \
  $(TOP)/src/vdbeaux.c \
  $(TOP)/src/vdbeblob.c \
  $(TOP)/src/vdbemem.c \

  $(TOP)/src/vdbeInt.h \
  $(TOP)/src/vtab.c \
  $(TOP)/src/walker.c \
  $(TOP)/src/where.c

# Generated source code files
#
................................................................................
  $(TOP)/ext/fts2/fts2_porter.c \
  $(TOP)/ext/fts2/fts2_tokenizer.h \
  $(TOP)/ext/fts2/fts2_tokenizer.c \
  $(TOP)/ext/fts2/fts2_tokenizer1.c
SRC += \
  $(TOP)/ext/fts3/fts3.c \
  $(TOP)/ext/fts3/fts3.h \
  $(TOP)/ext/fts3/fts3_expr.c \
  $(TOP)/ext/fts3/fts3_expr.h \
  $(TOP)/ext/fts3/fts3_hash.c \
  $(TOP)/ext/fts3/fts3_hash.h \
  $(TOP)/ext/fts3/fts3_icu.c \
  $(TOP)/ext/fts3/fts3_porter.c \

  $(TOP)/ext/fts3/fts3_tokenizer.h \
  $(TOP)/ext/fts3/fts3_tokenizer.c \
  $(TOP)/ext/fts3/fts3_tokenizer1.c

SRC += \
  $(TOP)/ext/icu/sqliteicu.h \
  $(TOP)/ext/icu/icu.c
SRC += \
  $(TOP)/ext/rtree/rtree.h \
  $(TOP)/ext/rtree/rtree.c
SRC += \
................................................................................
  $(TOP)/src/tokenize.c \
  $(TOP)/src/utf.c \
  $(TOP)/src/util.c \
  $(TOP)/src/vdbe.c \
  $(TOP)/src/vdbeapi.c \
  $(TOP)/src/vdbeaux.c \
  $(TOP)/src/vdbemem.c \

  $(TOP)/src/where.c \
  parse.c

# Source code to the actual test files.
#
TESTSRC = \
  $(TOP)/src/test1.c \
................................................................................
  $(TOP)/src/test_backup.c \
  $(TOP)/src/test_btree.c \
  $(TOP)/src/test_config.c \
  $(TOP)/src/test_devsym.c \
  $(TOP)/src/test_func.c \
  $(TOP)/src/test_hexio.c \
  $(TOP)/src/test_init.c \

  $(TOP)/src/test_journal.c \
  $(TOP)/src/test_malloc.c \
  $(TOP)/src/test_mutex.c \
  $(TOP)/src/test_onefile.c \
  $(TOP)/src/test_osinst.c \
  $(TOP)/src/test_pcache.c \
  $(TOP)/src/test_schema.c \
................................................................................
  $(TOP)/ext/fts1/fts1_tokenizer.h
HDR += \
  $(TOP)/ext/fts2/fts2.h \
  $(TOP)/ext/fts2/fts2_hash.h \
  $(TOP)/ext/fts2/fts2_tokenizer.h
HDR += \
  $(TOP)/ext/fts3/fts3.h \
  $(TOP)/ext/fts3/fts3_expr.h \
  $(TOP)/ext/fts3/fts3_hash.h \
  $(TOP)/ext/fts3/fts3_tokenizer.h
HDR += \
  $(TOP)/ext/rtree/rtree.h
HDR += \
  $(TOP)/ext/icu/sqliteicu.h
HDR += \
  $(TOP)/ext/sqlrr/sqlrr.h
  
# If using the amalgamation, use sqlite3.c directly to build the test
# fixture.  Otherwise link against libsqlite3.la.  (This distinction is
# necessary because the test fixture requires non-API symbols which are
# hidden when the library is built via the amalgamation).
#
TESTFIXTURE_SRC0 = $(TESTSRC2) libsqlite3.la
TESTFIXTURE_SRC1 = sqlite3.c
................................................................................

Makefile: $(TOP)/Makefile.in
	./config.status

sqlite3.pc: $(TOP)/sqlite3.pc.in
	./config.status

# Generate the file "last_change" which contains the date of change
# of the most recently modified source code file
#
last_change:	$(SRC)
	cat $(SRC) | grep '$$Id: ' | sort -k 5 | tail -1 \
          | $(NAWK) '{print $$5,$$6}' >last_change

libsqlite3.la:	$(LIBOBJ)
	$(LTLINK) -o $@ $(LIBOBJ) $(TLIBS) \
		${ALLOWRELEASE} -rpath "$(libdir)" -version-info "8:6:8"

libtclsqlite3.la:	tclsqlite.lo libsqlite3.la
	$(LTLINK) -o $@ tclsqlite.lo \
		libsqlite3.la @TCL_STUB_LIB_SPEC@ $(TLIBS) \
................................................................................

vdbeblob.lo:	$(TOP)/src/vdbeblob.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/vdbeblob.c

vdbemem.lo:	$(TOP)/src/vdbemem.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/vdbemem.c




vtab.lo:	$(TOP)/src/vtab.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/vtab.c

walker.lo:	$(TOP)/src/walker.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/walker.c

where.lo:	$(TOP)/src/where.c $(HDR)

        memjournal.lo \
        mutex.lo mutex_noop.lo mutex_os2.lo mutex_unix.lo mutex_w32.lo \
        notify.lo opcodes.lo os.lo os_unix.lo os_win.lo os_os2.lo \
        pager.lo parse.lo pcache.lo pcache1.lo pragma.lo prepare.lo printf.lo \
        random.lo resolve.lo rowset.lo select.lo status.lo \
        table.lo tokenize.lo trigger.lo update.lo \
        util.lo vacuum.lo \
        vdbe.lo vdbeapi.lo vdbeaux.lo vdbeblob.lo vdbemem.lo vdbetrace.lo \
        walker.lo where.lo utf.lo vtab.lo

# Object files for the amalgamation.
#
OBJS1 = sqlite3.lo

# Determine the real value of LIBOBJ based on the 'configure' script
................................................................................
  $(TOP)/src/vacuum.c \
  $(TOP)/src/vdbe.c \
  $(TOP)/src/vdbe.h \
  $(TOP)/src/vdbeapi.c \
  $(TOP)/src/vdbeaux.c \
  $(TOP)/src/vdbeblob.c \
  $(TOP)/src/vdbemem.c \
  $(TOP)/src/vdbetrace.c \
  $(TOP)/src/vdbeInt.h \
  $(TOP)/src/vtab.c \
  $(TOP)/src/walker.c \
  $(TOP)/src/where.c

# Generated source code files
#
................................................................................
  $(TOP)/ext/fts2/fts2_porter.c \
  $(TOP)/ext/fts2/fts2_tokenizer.h \
  $(TOP)/ext/fts2/fts2_tokenizer.c \
  $(TOP)/ext/fts2/fts2_tokenizer1.c
SRC += \
  $(TOP)/ext/fts3/fts3.c \
  $(TOP)/ext/fts3/fts3.h \
  $(TOP)/ext/fts3/fts3Int.h \
  $(TOP)/ext/fts3/fts3_expr.c \
  $(TOP)/ext/fts3/fts3_hash.c \
  $(TOP)/ext/fts3/fts3_hash.h \
  $(TOP)/ext/fts3/fts3_icu.c \
  $(TOP)/ext/fts3/fts3_porter.c \
  $(TOP)/ext/fts3/fts3_snippet.c \
  $(TOP)/ext/fts3/fts3_tokenizer.h \
  $(TOP)/ext/fts3/fts3_tokenizer.c \
  $(TOP)/ext/fts3/fts3_tokenizer1.c \
  $(TOP)/ext/fts3/fts3_write.c
SRC += \
  $(TOP)/ext/icu/sqliteicu.h \
  $(TOP)/ext/icu/icu.c
SRC += \
  $(TOP)/ext/rtree/rtree.h \
  $(TOP)/ext/rtree/rtree.c
SRC += \
................................................................................
  $(TOP)/src/tokenize.c \
  $(TOP)/src/utf.c \
  $(TOP)/src/util.c \
  $(TOP)/src/vdbe.c \
  $(TOP)/src/vdbeapi.c \
  $(TOP)/src/vdbeaux.c \
  $(TOP)/src/vdbemem.c \
  $(TOP)/src/vdbetrace.c \
  $(TOP)/src/where.c \
  parse.c

# Source code to the actual test files.
#
TESTSRC = \
  $(TOP)/src/test1.c \
................................................................................
  $(TOP)/src/test_backup.c \
  $(TOP)/src/test_btree.c \
  $(TOP)/src/test_config.c \
  $(TOP)/src/test_devsym.c \
  $(TOP)/src/test_func.c \
  $(TOP)/src/test_hexio.c \
  $(TOP)/src/test_init.c \
  $(TOP)/src/test_intarray.c \
  $(TOP)/src/test_journal.c \
  $(TOP)/src/test_malloc.c \
  $(TOP)/src/test_mutex.c \
  $(TOP)/src/test_onefile.c \
  $(TOP)/src/test_osinst.c \
  $(TOP)/src/test_pcache.c \
  $(TOP)/src/test_schema.c \
................................................................................
  $(TOP)/ext/fts1/fts1_tokenizer.h
HDR += \
  $(TOP)/ext/fts2/fts2.h \
  $(TOP)/ext/fts2/fts2_hash.h \
  $(TOP)/ext/fts2/fts2_tokenizer.h
HDR += \
  $(TOP)/ext/fts3/fts3.h \
  $(TOP)/ext/fts3/fts3Int.h \
  $(TOP)/ext/fts3/fts3_hash.h \
  $(TOP)/ext/fts3/fts3_tokenizer.h
HDR += \
  $(TOP)/ext/rtree/rtree.h
HDR += \
  $(TOP)/ext/icu/sqliteicu.h
HDR += \
  $(TOP)/ext/sqlrr/sqlrr.h

# If using the amalgamation, use sqlite3.c directly to build the test
# fixture.  Otherwise link against libsqlite3.la.  (This distinction is
# necessary because the test fixture requires non-API symbols which are
# hidden when the library is built via the amalgamation).
#
TESTFIXTURE_SRC0 = $(TESTSRC2) libsqlite3.la
TESTFIXTURE_SRC1 = sqlite3.c
................................................................................

Makefile: $(TOP)/Makefile.in
	./config.status

sqlite3.pc: $(TOP)/sqlite3.pc.in
	./config.status








libsqlite3.la:	$(LIBOBJ)
	$(LTLINK) -o $@ $(LIBOBJ) $(TLIBS) \
		${ALLOWRELEASE} -rpath "$(libdir)" -version-info "8:6:8"

libtclsqlite3.la:	tclsqlite.lo libsqlite3.la
	$(LTLINK) -o $@ tclsqlite.lo \
		libsqlite3.la @TCL_STUB_LIB_SPEC@ $(TLIBS) \
................................................................................

vdbeblob.lo:	$(TOP)/src/vdbeblob.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/vdbeblob.c

vdbemem.lo:	$(TOP)/src/vdbemem.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/vdbemem.c

vdbetrace.lo:	$(TOP)/src/vdbetrace.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/vdbetrace.c

vtab.lo:	$(TOP)/src/vtab.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/vtab.c

walker.lo:	$(TOP)/src/walker.c $(HDR)
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/walker.c

where.lo:	$(TOP)/src/where.c $(HDR)

3.6.20

3.6.21

#! /bin/sh
# Guess values for system-dependent variables and create Makefiles.
# Generated by GNU Autoconf 2.62 for sqlite 3.6.20.
#
# Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
# 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
# This configure script is free software; the Free Software Foundation
# gives unlimited permission to copy, distribute and modify it.
## --------------------- ##
## M4sh Initialization.  ##
................................................................................
MFLAGS=
MAKEFLAGS=
SHELL=${CONFIG_SHELL-/bin/sh}

# Identity of this package.
PACKAGE_NAME='sqlite'
PACKAGE_TARNAME='sqlite'
PACKAGE_VERSION='3.6.20'
PACKAGE_STRING='sqlite 3.6.20'
PACKAGE_BUGREPORT=''

# Factoring default headers for most tests.
ac_includes_default="\
#include <stdio.h>
#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h>
................................................................................
#
# Report the --help message.
#
if test "$ac_init_help" = "long"; then
  # Omit some internal or obsolete options to make the list less imposing.
  # This message is too long to be a string in the A/UX 3.1 sh.
  cat <<_ACEOF
\`configure' configures sqlite 3.6.20 to adapt to many kinds of systems.

Usage: $0 [OPTION]... [VAR=VALUE]...

To assign environment variables (e.g., CC, CFLAGS...), specify them as
VAR=VALUE.  See below for descriptions of some of the useful variables.

Defaults for the options are specified in brackets.
................................................................................
  --build=BUILD     configure for building on BUILD [guessed]
  --host=HOST       cross-compile to build programs to run on HOST [BUILD]
_ACEOF
fi

if test -n "$ac_init_help"; then
  case $ac_init_help in
     short | recursive ) echo "Configuration of sqlite 3.6.20:";;
   esac
  cat <<\_ACEOF

Optional Features:
  --disable-option-checking  ignore unrecognized --enable/--with options
  --disable-FEATURE       do not include FEATURE (same as --enable-FEATURE=no)
  --enable-FEATURE[=ARG]  include FEATURE [ARG=yes]
................................................................................
    cd "$ac_pwd" || { ac_status=$?; break; }
  done
fi

test -n "$ac_init_help" && exit $ac_status
if $ac_init_version; then
  cat <<\_ACEOF
sqlite configure 3.6.20
generated by GNU Autoconf 2.62

Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
This configure script is free software; the Free Software Foundation
gives unlimited permission to copy, distribute and modify it.
_ACEOF
  exit
fi
cat >config.log <<_ACEOF
This file contains any messages produced by compilers while
running configure, to aid debugging if configure makes a mistake.

It was created by sqlite $as_me 3.6.20, which was
generated by GNU Autoconf 2.62.  Invocation command line was

  $ $0 $@

_ACEOF
exec 5>>config.log
{
................................................................................

exec 6>&1

# Save the log message, to keep $[0] and so on meaningful, and to
# report actual input values of CONFIG_FILES etc. instead of their
# values after options handling.
ac_log="
This file was extended by sqlite $as_me 3.6.20, which was
generated by GNU Autoconf 2.62.  Invocation command line was

  CONFIG_FILES    = $CONFIG_FILES
  CONFIG_HEADERS  = $CONFIG_HEADERS
  CONFIG_LINKS    = $CONFIG_LINKS
  CONFIG_COMMANDS = $CONFIG_COMMANDS
  $ $0 $@
................................................................................
$config_commands

Report bugs to <bug-autoconf@gnu.org>."

_ACEOF
cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
ac_cs_version="\\
sqlite config.status 3.6.20
configured by $0, generated by GNU Autoconf 2.62,
  with options \\"`$as_echo "$ac_configure_args" | sed 's/^ //; s/[\\""\`\$]/\\\\&/g'`\\"

Copyright (C) 2008 Free Software Foundation, Inc.
This config.status script is free software; the Free Software Foundation
gives unlimited permission to copy, distribute and modify it."

#! /bin/sh
# Guess values for system-dependent variables and create Makefiles.
# Generated by GNU Autoconf 2.62 for sqlite 3.6.21.
#
# Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
# 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
# This configure script is free software; the Free Software Foundation
# gives unlimited permission to copy, distribute and modify it.
## --------------------- ##
## M4sh Initialization.  ##
................................................................................
MFLAGS=
MAKEFLAGS=
SHELL=${CONFIG_SHELL-/bin/sh}

# Identity of this package.
PACKAGE_NAME='sqlite'
PACKAGE_TARNAME='sqlite'
PACKAGE_VERSION='3.6.21'
PACKAGE_STRING='sqlite 3.6.21'
PACKAGE_BUGREPORT=''

# Factoring default headers for most tests.
ac_includes_default="\
#include <stdio.h>
#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h>
................................................................................
#
# Report the --help message.
#
if test "$ac_init_help" = "long"; then
  # Omit some internal or obsolete options to make the list less imposing.
  # This message is too long to be a string in the A/UX 3.1 sh.
  cat <<_ACEOF
\`configure' configures sqlite 3.6.21 to adapt to many kinds of systems.

Usage: $0 [OPTION]... [VAR=VALUE]...

To assign environment variables (e.g., CC, CFLAGS...), specify them as
VAR=VALUE.  See below for descriptions of some of the useful variables.

Defaults for the options are specified in brackets.
................................................................................
  --build=BUILD     configure for building on BUILD [guessed]
  --host=HOST       cross-compile to build programs to run on HOST [BUILD]
_ACEOF
fi

if test -n "$ac_init_help"; then
  case $ac_init_help in
     short | recursive ) echo "Configuration of sqlite 3.6.21:";;
   esac
  cat <<\_ACEOF

Optional Features:
  --disable-option-checking  ignore unrecognized --enable/--with options
  --disable-FEATURE       do not include FEATURE (same as --enable-FEATURE=no)
  --enable-FEATURE[=ARG]  include FEATURE [ARG=yes]
................................................................................
    cd "$ac_pwd" || { ac_status=$?; break; }
  done
fi

test -n "$ac_init_help" && exit $ac_status
if $ac_init_version; then
  cat <<\_ACEOF
sqlite configure 3.6.21
generated by GNU Autoconf 2.62

Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
This configure script is free software; the Free Software Foundation
gives unlimited permission to copy, distribute and modify it.
_ACEOF
  exit
fi
cat >config.log <<_ACEOF
This file contains any messages produced by compilers while
running configure, to aid debugging if configure makes a mistake.

It was created by sqlite $as_me 3.6.21, which was
generated by GNU Autoconf 2.62.  Invocation command line was

  $ $0 $@

_ACEOF
exec 5>>config.log
{
................................................................................

exec 6>&1

# Save the log message, to keep $[0] and so on meaningful, and to
# report actual input values of CONFIG_FILES etc. instead of their
# values after options handling.
ac_log="
This file was extended by sqlite $as_me 3.6.21, which was
generated by GNU Autoconf 2.62.  Invocation command line was

  CONFIG_FILES    = $CONFIG_FILES
  CONFIG_HEADERS  = $CONFIG_HEADERS
  CONFIG_LINKS    = $CONFIG_LINKS
  CONFIG_COMMANDS = $CONFIG_COMMANDS
  $ $0 $@
................................................................................
$config_commands

Report bugs to <bug-autoconf@gnu.org>."

_ACEOF
cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
ac_cs_version="\\
sqlite config.status 3.6.21
configured by $0, generated by GNU Autoconf 2.62,
  with options \\"`$as_echo "$ac_configure_args" | sed 's/^ //; s/[\\""\`\$]/\\\\&/g'`\\"

Copyright (C) 2008 Free Software Foundation, Inc.
This config.status script is free software; the Free Software Foundation
gives unlimited permission to copy, distribute and modify it."

  /* Because of the way intra-process file locking works, this backend
  ** needs to return a canonical path. The following block assumes the
  ** file-system uses unix style paths. 
  */
  if( rc==SQLITE_OK ){
    int i, j;
    int n = nPathOut;
    char *z = zPathOut;

    while( n>1 && z[n-1]=='/' ){ n--; }
    for(i=j=0; i<n; i++){
      if( z[i]=='/' ){
        if( z[i+1]=='/' ) continue;
        if( z[i+1]=='.' && i+2<n && z[i+2]=='/' ){
          i += 1;
          continue;

  /* Because of the way intra-process file locking works, this backend
  ** needs to return a canonical path. The following block assumes the
  ** file-system uses unix style paths. 
  */
  if( rc==SQLITE_OK ){
    int i, j;

    char *z = zPathOut;
    int n = strlen(z);
    while( n>1 && z[n-1]=='/' ){ n--; }
    for(i=j=0; i<n; i++){
      if( z[i]=='/' ){
        if( z[i+1]=='/' ) continue;
        if( z[i+1]=='.' && i+2<n && z[i+2]=='/' ){
          i += 1;
          continue;

#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3)

#if defined(SQLITE_ENABLE_FTS3) && !defined(SQLITE_CORE)
# define SQLITE_CORE 1
#endif



#include <assert.h>
#include <stdlib.h>

#include <stdio.h>
#include <string.h>
#include <ctype.h>

#include "fts3.h"
#include "fts3_expr.h"
#include "fts3_hash.h"
#include "fts3_tokenizer.h"
#ifndef SQLITE_CORE 
# include "sqlite3ext.h"
  SQLITE_EXTENSION_INIT1
#endif



/* TODO(shess) MAN, this thing needs some refactoring.  At minimum, it
** would be nice to order the file better, perhaps something along the
** lines of:
**
**  - utility functions
................................................................................

#if 0
# define FTSTRACE(A)  printf A; fflush(stdout)
#else
# define FTSTRACE(A)
#endif

/* It is not safe to call isspace(), tolower(), or isalnum() on
** hi-bit-set characters.  This is the same solution used in the
** tokenizer.
*/
/* TODO(shess) The snippet-generation code should be using the
** tokenizer-generated tokens rather than doing its own local
** tokenization.
*/
/* TODO(shess) Is __isascii() a portable version of (c&0x80)==0? */
static int safe_isspace(char c){
  return (c&0x80)==0 ? isspace(c) : 0;
}
static int safe_tolower(char c){
  return (c&0x80)==0 ? tolower(c) : c;
}
static int safe_isalnum(char c){
  return (c&0x80)==0 ? isalnum(c) : 0;
}

typedef enum DocListType {
  DL_DOCIDS,              /* docids only */
  DL_POSITIONS,           /* docids + positions */
  DL_POSITIONS_OFFSETS    /* docids + positions + offsets */
} DocListType;

/*
................................................................................

enum {
  POS_END = 0,        /* end of this position list */
  POS_COLUMN,         /* followed by new column number */
  POS_BASE
};

/* MERGE_COUNT controls how often we merge segments (see comment at
** top of file).
*/
#define MERGE_COUNT 16

/* utility functions */

/* CLEAR() and SCRAMBLE() abstract memset() on a pointer to a single
** record to prevent errors of the form:
**
** my_function(SomeType *b){
**   memset(b, '\0', sizeof(b));  // sizeof(b)!=sizeof(*b)
................................................................................

#ifndef NDEBUG
#  define SCRAMBLE(b) memset(b, 0x55, sizeof(*(b)))
#else
#  define SCRAMBLE(b)
#endif

/* We may need up to VARINT_MAX bytes to store an encoded 64-bit integer. */
#define VARINT_MAX 10

/* Write a 64-bit variable-length integer to memory starting at p[0].
 * The length of data written will be between 1 and VARINT_MAX bytes.
 * The number of bytes written is returned. */

static int fts3PutVarint(char *p, sqlite_int64 v){
  unsigned char *q = (unsigned char *) p;
  sqlite_uint64 vu = v;
  do{
    *q++ = (unsigned char) ((vu & 0x7f) | 0x80);
    vu >>= 7;
  }while( vu!=0 );
  q[-1] &= 0x7f;  /* turn off high bit in final byte */
  assert( q - (unsigned char *)p <= VARINT_MAX );
  return (int) (q - (unsigned char *)p);
}


/* Read a 64-bit variable-length integer from memory starting at p[0].
 * Return the number of bytes read, or 0 on error.
 * The value is stored in *v. */

static int fts3GetVarint(const char *p, sqlite_int64 *v){
  const unsigned char *q = (const unsigned char *) p;
  sqlite_uint64 x = 0, y = 1;
  while( (*q & 0x80) == 0x80 ){
    x += y * (*q++ & 0x7f);
    y <<= 7;
    if( q - (unsigned char *)p >= VARINT_MAX ){  /* bad data */
      assert( 0 );
      return 0;
    }
  }
  x += y * (*q++);
  *v = (sqlite_int64) x;
  return (int) (q - (unsigned char *)p);
}





static int fts3GetVarint32(const char *p, int *pi){
 sqlite_int64 i;
 int ret = fts3GetVarint(p, &i);
 *pi = (int) i;
 assert( *pi==i );
 return ret;
}

/*******************************************************************/
/* DataBuffer is used to collect data into a buffer in piecemeal
** fashion.  It implements the usual distinction between amount of
** data currently stored (nData) and buffer capacity (nCapacity).
**
** dataBufferInit - create a buffer with given initial capacity.
** dataBufferReset - forget buffer's data, retaining capacity.
** dataBufferDestroy - free buffer's data.
** dataBufferSwap - swap contents of two buffers.
** dataBufferExpand - expand capacity without adding data.
** dataBufferAppend - append data.
** dataBufferAppend2 - append two pieces of data at once.
** dataBufferReplace - replace buffer's data.
*/
typedef struct DataBuffer {
  char *pData;          /* Pointer to malloc'ed buffer. */
  int nCapacity;        /* Size of pData buffer. */
  int nData;            /* End of data loaded into pData. */
} DataBuffer;

static void dataBufferInit(DataBuffer *pBuffer, int nCapacity){
  assert( nCapacity>=0 );
  pBuffer->nData = 0;
  pBuffer->nCapacity = nCapacity;
  pBuffer->pData = nCapacity==0 ? NULL : sqlite3_malloc(nCapacity);
}
static void dataBufferReset(DataBuffer *pBuffer){
  pBuffer->nData = 0;
}
static void dataBufferDestroy(DataBuffer *pBuffer){
  if( pBuffer->pData!=NULL ) sqlite3_free(pBuffer->pData);
  SCRAMBLE(pBuffer);
}
static void dataBufferSwap(DataBuffer *pBuffer1, DataBuffer *pBuffer2){
  DataBuffer tmp = *pBuffer1;
  *pBuffer1 = *pBuffer2;
  *pBuffer2 = tmp;
}
static void dataBufferExpand(DataBuffer *pBuffer, int nAddCapacity){
  assert( nAddCapacity>0 );
  /* TODO(shess) Consider expanding more aggressively.  Note that the
  ** underlying malloc implementation may take care of such things for
  ** us already.
  */
  if( pBuffer->nData+nAddCapacity>pBuffer->nCapacity ){
    pBuffer->nCapacity = pBuffer->nData+nAddCapacity;
    pBuffer->pData = sqlite3_realloc(pBuffer->pData, pBuffer->nCapacity);
  }
}
static void dataBufferAppend(DataBuffer *pBuffer,
                             const char *pSource, int nSource){
  assert( nSource>0 && pSource!=NULL );
  dataBufferExpand(pBuffer, nSource);
  memcpy(pBuffer->pData+pBuffer->nData, pSource, nSource);
  pBuffer->nData += nSource;
}
static void dataBufferAppend2(DataBuffer *pBuffer,
                              const char *pSource1, int nSource1,
                              const char *pSource2, int nSource2){
  assert( nSource1>0 && pSource1!=NULL );
  assert( nSource2>0 && pSource2!=NULL );
  dataBufferExpand(pBuffer, nSource1+nSource2);
  memcpy(pBuffer->pData+pBuffer->nData, pSource1, nSource1);
  memcpy(pBuffer->pData+pBuffer->nData+nSource1, pSource2, nSource2);
  pBuffer->nData += nSource1+nSource2;
}
static void dataBufferReplace(DataBuffer *pBuffer,
                              const char *pSource, int nSource){
  dataBufferReset(pBuffer);
  dataBufferAppend(pBuffer, pSource, nSource);
}

/* StringBuffer is a null-terminated version of DataBuffer. */
typedef struct StringBuffer {
  DataBuffer b;            /* Includes null terminator. */
} StringBuffer;

static void initStringBuffer(StringBuffer *sb){
  dataBufferInit(&sb->b, 100);
  dataBufferReplace(&sb->b, "", 1);
}
static int stringBufferLength(StringBuffer *sb){
  return sb->b.nData-1;
}
static char *stringBufferData(StringBuffer *sb){
  return sb->b.pData;
}
static void stringBufferDestroy(StringBuffer *sb){
  dataBufferDestroy(&sb->b);
}

static void nappend(StringBuffer *sb, const char *zFrom, int nFrom){
  assert( sb->b.nData>0 );
  if( nFrom>0 ){
    sb->b.nData--;
    dataBufferAppend2(&sb->b, zFrom, nFrom, "", 1);
  }
}
static void append(StringBuffer *sb, const char *zFrom){
  nappend(sb, zFrom, strlen(zFrom));
}

/* Append a list of strings separated by commas. */
static void appendList(StringBuffer *sb, int nString, char **azString){
  int i;
  for(i=0; i<nString; ++i){
    if( i>0 ) append(sb, ", ");
    append(sb, azString[i]);
  }
}

static int endsInWhiteSpace(StringBuffer *p){
  return stringBufferLength(p)>0 &&
    safe_isspace(stringBufferData(p)[stringBufferLength(p)-1]);
}

/* If the StringBuffer ends in something other than white space, add a
** single space character to the end.
*/
static void appendWhiteSpace(StringBuffer *p){
  if( stringBufferLength(p)==0 ) return;
  if( !endsInWhiteSpace(p) ) append(p, " ");
}

/* Remove white space from the end of the StringBuffer */
static void trimWhiteSpace(StringBuffer *p){
  while( endsInWhiteSpace(p) ){
    p->b.pData[--p->b.nData-1] = '\0';
  }
}

/*******************************************************************/
/* DLReader is used to read document elements from a doclist.  The
** current docid is cached, so dlrDocid() is fast.  DLReader does not
** own the doclist buffer.
**
** dlrAtEnd - true if there's no more data to read.
** dlrDocid - docid of current document.
** dlrDocData - doclist data for current document (including docid).
** dlrDocDataBytes - length of same.
** dlrAllDataBytes - length of all remaining data.
** dlrPosData - position data for current document.
** dlrPosDataLen - length of pos data for current document (incl POS_END).
** dlrStep - step to current document.
** dlrInit - initial for doclist of given type against given data.
** dlrDestroy - clean up.
**
** Expected usage is something like:
**
**   DLReader reader;
**   dlrInit(&reader, pData, nData);
**   while( !dlrAtEnd(&reader) ){
**     // calls to dlrDocid() and kin.
**     dlrStep(&reader);
**   }
**   dlrDestroy(&reader);
*/
typedef struct DLReader {
  DocListType iType;
  const char *pData;
  int nData;

  sqlite_int64 iDocid;
  int nElement;
} DLReader;

static int dlrAtEnd(DLReader *pReader){
  assert( pReader->nData>=0 );
  return pReader->nData==0;
}
static sqlite_int64 dlrDocid(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );
  return pReader->iDocid;
}
static const char *dlrDocData(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );
  return pReader->pData;
}
static int dlrDocDataBytes(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );
  return pReader->nElement;
}
static int dlrAllDataBytes(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );
  return pReader->nData;
}
/* TODO(shess) Consider adding a field to track iDocid varint length
** to make these two functions faster.  This might matter (a tiny bit)
** for queries.
*/
static const char *dlrPosData(DLReader *pReader){
  sqlite_int64 iDummy;
  int n = fts3GetVarint(pReader->pData, &iDummy);
  assert( !dlrAtEnd(pReader) );
  return pReader->pData+n;
}
static int dlrPosDataLen(DLReader *pReader){
  sqlite_int64 iDummy;
  int n = fts3GetVarint(pReader->pData, &iDummy);
  assert( !dlrAtEnd(pReader) );
  return pReader->nElement-n;
}
static void dlrStep(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );

  /* Skip past current doclist element. */
  assert( pReader->nElement<=pReader->nData );
  pReader->pData += pReader->nElement;
  pReader->nData -= pReader->nElement;

  /* If there is more data, read the next doclist element. */
  if( pReader->nData!=0 ){
    sqlite_int64 iDocidDelta;
    int iDummy, n = fts3GetVarint(pReader->pData, &iDocidDelta);
    pReader->iDocid += iDocidDelta;
    if( pReader->iType>=DL_POSITIONS ){
      assert( n<pReader->nData );
      while( 1 ){
        n += fts3GetVarint32(pReader->pData+n, &iDummy);
        assert( n<=pReader->nData );
        if( iDummy==POS_END ) break;
        if( iDummy==POS_COLUMN ){
          n += fts3GetVarint32(pReader->pData+n, &iDummy);
          assert( n<pReader->nData );
        }else if( pReader->iType==DL_POSITIONS_OFFSETS ){
          n += fts3GetVarint32(pReader->pData+n, &iDummy);
          n += fts3GetVarint32(pReader->pData+n, &iDummy);
          assert( n<pReader->nData );
        }
      }
    }
    pReader->nElement = n;
    assert( pReader->nElement<=pReader->nData );
  }
}
static void dlrInit(DLReader *pReader, DocListType iType,
                    const char *pData, int nData){
  assert( pData!=NULL && nData!=0 );
  pReader->iType = iType;
  pReader->pData = pData;
  pReader->nData = nData;
  pReader->nElement = 0;
  pReader->iDocid = 0;

  /* Load the first element's data.  There must be a first element. */
  dlrStep(pReader);
}
static void dlrDestroy(DLReader *pReader){
  SCRAMBLE(pReader);
}

#ifndef NDEBUG
/* Verify that the doclist can be validly decoded.  Also returns the
** last docid found because it is convenient in other assertions for
** DLWriter.
*/
static void docListValidate(DocListType iType, const char *pData, int nData,
                            sqlite_int64 *pLastDocid){
  sqlite_int64 iPrevDocid = 0;
  assert( nData>0 );
  assert( pData!=0 );
  assert( pData+nData>pData );
  while( nData!=0 ){
    sqlite_int64 iDocidDelta;
    int n = fts3GetVarint(pData, &iDocidDelta);
    iPrevDocid += iDocidDelta;
    if( iType>DL_DOCIDS ){
      int iDummy;
      while( 1 ){
        n += fts3GetVarint32(pData+n, &iDummy);
        if( iDummy==POS_END ) break;
        if( iDummy==POS_COLUMN ){
          n += fts3GetVarint32(pData+n, &iDummy);
        }else if( iType>DL_POSITIONS ){
          n += fts3GetVarint32(pData+n, &iDummy);
          n += fts3GetVarint32(pData+n, &iDummy);
        }
        assert( n<=nData );
      }
    }
    assert( n<=nData );
    pData += n;
    nData -= n;
  }
  if( pLastDocid ) *pLastDocid = iPrevDocid;
}
#define ASSERT_VALID_DOCLIST(i, p, n, o) docListValidate(i, p, n, o)
#else
#define ASSERT_VALID_DOCLIST(i, p, n, o) assert( 1 )
#endif

/*******************************************************************/
/* DLWriter is used to write doclist data to a DataBuffer.  DLWriter
** always appends to the buffer and does not own it.
**
** dlwInit - initialize to write a given type doclistto a buffer.
** dlwDestroy - clear the writer's memory.  Does not free buffer.
** dlwAppend - append raw doclist data to buffer.
** dlwCopy - copy next doclist from reader to writer.
** dlwAdd - construct doclist element and append to buffer.
**    Only apply dlwAdd() to DL_DOCIDS doclists (else use PLWriter).
*/
typedef struct DLWriter {
  DocListType iType;
  DataBuffer *b;
  sqlite_int64 iPrevDocid;
#ifndef NDEBUG
  int has_iPrevDocid;
#endif
} DLWriter;

static void dlwInit(DLWriter *pWriter, DocListType iType, DataBuffer *b){
  pWriter->b = b;
  pWriter->iType = iType;
  pWriter->iPrevDocid = 0;
#ifndef NDEBUG
  pWriter->has_iPrevDocid = 0;
#endif
}
static void dlwDestroy(DLWriter *pWriter){
  SCRAMBLE(pWriter);
}
/* iFirstDocid is the first docid in the doclist in pData.  It is
** needed because pData may point within a larger doclist, in which
** case the first item would be delta-encoded.
**
** iLastDocid is the final docid in the doclist in pData.  It is
** needed to create the new iPrevDocid for future delta-encoding.  The
** code could decode the passed doclist to recreate iLastDocid, but
** the only current user (docListMerge) already has decoded this
** information.
*/
/* TODO(shess) This has become just a helper for docListMerge.
** Consider a refactor to make this cleaner.
*/
static void dlwAppend(DLWriter *pWriter,
                      const char *pData, int nData,
                      sqlite_int64 iFirstDocid, sqlite_int64 iLastDocid){
  sqlite_int64 iDocid = 0;
  char c[VARINT_MAX];
  int nFirstOld, nFirstNew;     /* Old and new varint len of first docid. */
#ifndef NDEBUG
  sqlite_int64 iLastDocidDelta;
#endif

  /* Recode the initial docid as delta from iPrevDocid. */
  nFirstOld = fts3GetVarint(pData, &iDocid);
  assert( nFirstOld<nData || (nFirstOld==nData && pWriter->iType==DL_DOCIDS) );
  nFirstNew = fts3PutVarint(c, iFirstDocid-pWriter->iPrevDocid);

  /* Verify that the incoming doclist is valid AND that it ends with
  ** the expected docid.  This is essential because we'll trust this
  ** docid in future delta-encoding.
  */
  ASSERT_VALID_DOCLIST(pWriter->iType, pData, nData, &iLastDocidDelta);
  assert( iLastDocid==iFirstDocid-iDocid+iLastDocidDelta );

  /* Append recoded initial docid and everything else.  Rest of docids
  ** should have been delta-encoded from previous initial docid.
  */
  if( nFirstOld<nData ){
    dataBufferAppend2(pWriter->b, c, nFirstNew,
                      pData+nFirstOld, nData-nFirstOld);
  }else{
    dataBufferAppend(pWriter->b, c, nFirstNew);
  }
  pWriter->iPrevDocid = iLastDocid;
}
static void dlwCopy(DLWriter *pWriter, DLReader *pReader){
  dlwAppend(pWriter, dlrDocData(pReader), dlrDocDataBytes(pReader),
            dlrDocid(pReader), dlrDocid(pReader));
}
static void dlwAdd(DLWriter *pWriter, sqlite_int64 iDocid){
  char c[VARINT_MAX];
  int n = fts3PutVarint(c, iDocid-pWriter->iPrevDocid);

  /* Docids must ascend. */
  assert( !pWriter->has_iPrevDocid || iDocid>pWriter->iPrevDocid );
  assert( pWriter->iType==DL_DOCIDS );

  dataBufferAppend(pWriter->b, c, n);
  pWriter->iPrevDocid = iDocid;
#ifndef NDEBUG
  pWriter->has_iPrevDocid = 1;
#endif
}

/*******************************************************************/
/* PLReader is used to read data from a document's position list.  As
** the caller steps through the list, data is cached so that varints
** only need to be decoded once.
**
** plrInit, plrDestroy - create/destroy a reader.
** plrColumn, plrPosition, plrStartOffset, plrEndOffset - accessors
** plrAtEnd - at end of stream, only call plrDestroy once true.
** plrStep - step to the next element.
*/
typedef struct PLReader {
  /* These refer to the next position's data.  nData will reach 0 when
  ** reading the last position, so plrStep() signals EOF by setting
  ** pData to NULL.
  */
  const char *pData;
  int nData;

  DocListType iType;
  int iColumn;         /* the last column read */
  int iPosition;       /* the last position read */
  int iStartOffset;    /* the last start offset read */
  int iEndOffset;      /* the last end offset read */
} PLReader;

static int plrAtEnd(PLReader *pReader){
  return pReader->pData==NULL;
}
static int plrColumn(PLReader *pReader){
  assert( !plrAtEnd(pReader) );
  return pReader->iColumn;
}
static int plrPosition(PLReader *pReader){
  assert( !plrAtEnd(pReader) );
  return pReader->iPosition;
}
static int plrStartOffset(PLReader *pReader){
  assert( !plrAtEnd(pReader) );
  return pReader->iStartOffset;
}
static int plrEndOffset(PLReader *pReader){
  assert( !plrAtEnd(pReader) );
  return pReader->iEndOffset;
}
static void plrStep(PLReader *pReader){
  int i, n;

  assert( !plrAtEnd(pReader) );

  if( pReader->nData==0 ){
    pReader->pData = NULL;
    return;
  }

  n = fts3GetVarint32(pReader->pData, &i);
  if( i==POS_COLUMN ){
    n += fts3GetVarint32(pReader->pData+n, &pReader->iColumn);
    pReader->iPosition = 0;
    pReader->iStartOffset = 0;
    n += fts3GetVarint32(pReader->pData+n, &i);
  }
  /* Should never see adjacent column changes. */
  assert( i!=POS_COLUMN );

  if( i==POS_END ){
    pReader->nData = 0;
    pReader->pData = NULL;
    return;
  }

  pReader->iPosition += i-POS_BASE;
  if( pReader->iType==DL_POSITIONS_OFFSETS ){
    n += fts3GetVarint32(pReader->pData+n, &i);
    pReader->iStartOffset += i;
    n += fts3GetVarint32(pReader->pData+n, &i);
    pReader->iEndOffset = pReader->iStartOffset+i;
  }
  assert( n<=pReader->nData );
  pReader->pData += n;
  pReader->nData -= n;
}

static void plrInit(PLReader *pReader, DLReader *pDLReader){
  pReader->pData = dlrPosData(pDLReader);
  pReader->nData = dlrPosDataLen(pDLReader);
  pReader->iType = pDLReader->iType;
  pReader->iColumn = 0;
  pReader->iPosition = 0;
  pReader->iStartOffset = 0;
  pReader->iEndOffset = 0;
  plrStep(pReader);
}
static void plrDestroy(PLReader *pReader){
  SCRAMBLE(pReader);
}

/*******************************************************************/
/* PLWriter is used in constructing a document's position list.  As a
** convenience, if iType is DL_DOCIDS, PLWriter becomes a no-op.
** PLWriter writes to the associated DLWriter's buffer.
**
** plwInit - init for writing a document's poslist.
** plwDestroy - clear a writer.
** plwAdd - append position and offset information.
** plwCopy - copy next position's data from reader to writer.
** plwTerminate - add any necessary doclist terminator.
**
** Calling plwAdd() after plwTerminate() may result in a corrupt
** doclist.
*/
/* TODO(shess) Until we've written the second item, we can cache the
** first item's information.  Then we'd have three states:
**
** - initialized with docid, no positions.
** - docid and one position.
** - docid and multiple positions.
**
** Only the last state needs to actually write to dlw->b, which would
** be an improvement in the DLCollector case.
*/
typedef struct PLWriter {
  DLWriter *dlw;

  int iColumn;    /* the last column written */
  int iPos;       /* the last position written */
  int iOffset;    /* the last start offset written */
} PLWriter;

/* TODO(shess) In the case where the parent is reading these values
** from a PLReader, we could optimize to a copy if that PLReader has
** the same type as pWriter.
*/
static void plwAdd(PLWriter *pWriter, int iColumn, int iPos,
                   int iStartOffset, int iEndOffset){
  /* Worst-case space for POS_COLUMN, iColumn, iPosDelta,
  ** iStartOffsetDelta, and iEndOffsetDelta.
  */
  char c[5*VARINT_MAX];
  int n = 0;

  /* Ban plwAdd() after plwTerminate(). */
  assert( pWriter->iPos!=-1 );

  if( pWriter->dlw->iType==DL_DOCIDS ) return;

  if( iColumn!=pWriter->iColumn ){
    n += fts3PutVarint(c+n, POS_COLUMN);
    n += fts3PutVarint(c+n, iColumn);
    pWriter->iColumn = iColumn;
    pWriter->iPos = 0;
    pWriter->iOffset = 0;
  }
  assert( iPos>=pWriter->iPos );
  n += fts3PutVarint(c+n, POS_BASE+(iPos-pWriter->iPos));
  pWriter->iPos = iPos;
  if( pWriter->dlw->iType==DL_POSITIONS_OFFSETS ){
    assert( iStartOffset>=pWriter->iOffset );
    n += fts3PutVarint(c+n, iStartOffset-pWriter->iOffset);
    pWriter->iOffset = iStartOffset;
    assert( iEndOffset>=iStartOffset );
    n += fts3PutVarint(c+n, iEndOffset-iStartOffset);
  }
  dataBufferAppend(pWriter->dlw->b, c, n);
}
static void plwCopy(PLWriter *pWriter, PLReader *pReader){
  plwAdd(pWriter, plrColumn(pReader), plrPosition(pReader),
         plrStartOffset(pReader), plrEndOffset(pReader));
}
static void plwInit(PLWriter *pWriter, DLWriter *dlw, sqlite_int64 iDocid){
  char c[VARINT_MAX];
  int n;

  pWriter->dlw = dlw;

  /* Docids must ascend. */
  assert( !pWriter->dlw->has_iPrevDocid || iDocid>pWriter->dlw->iPrevDocid );
  n = fts3PutVarint(c, iDocid-pWriter->dlw->iPrevDocid);
  dataBufferAppend(pWriter->dlw->b, c, n);
  pWriter->dlw->iPrevDocid = iDocid;
#ifndef NDEBUG
  pWriter->dlw->has_iPrevDocid = 1;
#endif

  pWriter->iColumn = 0;
  pWriter->iPos = 0;
  pWriter->iOffset = 0;
}
/* TODO(shess) Should plwDestroy() also terminate the doclist?  But
** then plwDestroy() would no longer be just a destructor, it would
** also be doing work, which isn't consistent with the overall idiom.
** Another option would be for plwAdd() to always append any necessary
** terminator, so that the output is always correct.  But that would
** add incremental work to the common case with the only benefit being
** API elegance.  Punt for now.
*/
static void plwTerminate(PLWriter *pWriter){
  if( pWriter->dlw->iType>DL_DOCIDS ){
    char c[VARINT_MAX];
    int n = fts3PutVarint(c, POS_END);
    dataBufferAppend(pWriter->dlw->b, c, n);
  }
#ifndef NDEBUG
  /* Mark as terminated for assert in plwAdd(). */
  pWriter->iPos = -1;
#endif
}
static void plwDestroy(PLWriter *pWriter){
  SCRAMBLE(pWriter);
}

/*******************************************************************/
/* DLCollector wraps PLWriter and DLWriter to provide a
** dynamically-allocated doclist area to use during tokenization.
**
** dlcNew - malloc up and initialize a collector.
** dlcDelete - destroy a collector and all contained items.
** dlcAddPos - append position and offset information.
** dlcAddDoclist - add the collected doclist to the given buffer.
** dlcNext - terminate the current document and open another.
*/
typedef struct DLCollector {
  DataBuffer b;
  DLWriter dlw;
  PLWriter plw;
} DLCollector;

/* TODO(shess) This could also be done by calling plwTerminate() and
** dataBufferAppend().  I tried that, expecting nominal performance
** differences, but it seemed to pretty reliably be worth 1% to code
** it this way.  I suspect it is the incremental malloc overhead (some
** percentage of the plwTerminate() calls will cause a realloc), so
** this might be worth revisiting if the DataBuffer implementation
** changes.
*/
static void dlcAddDoclist(DLCollector *pCollector, DataBuffer *b){
  if( pCollector->dlw.iType>DL_DOCIDS ){
    char c[VARINT_MAX];
    int n = fts3PutVarint(c, POS_END);
    dataBufferAppend2(b, pCollector->b.pData, pCollector->b.nData, c, n);
  }else{
    dataBufferAppend(b, pCollector->b.pData, pCollector->b.nData);
  }
}
static void dlcNext(DLCollector *pCollector, sqlite_int64 iDocid){
  plwTerminate(&pCollector->plw);
  plwDestroy(&pCollector->plw);
  plwInit(&pCollector->plw, &pCollector->dlw, iDocid);
}
static void dlcAddPos(DLCollector *pCollector, int iColumn, int iPos,
                      int iStartOffset, int iEndOffset){
  plwAdd(&pCollector->plw, iColumn, iPos, iStartOffset, iEndOffset);
}

static DLCollector *dlcNew(sqlite_int64 iDocid, DocListType iType){
  DLCollector *pCollector = sqlite3_malloc(sizeof(DLCollector));
  dataBufferInit(&pCollector->b, 0);
  dlwInit(&pCollector->dlw, iType, &pCollector->b);
  plwInit(&pCollector->plw, &pCollector->dlw, iDocid);
  return pCollector;
}
static void dlcDelete(DLCollector *pCollector){
  plwDestroy(&pCollector->plw);
  dlwDestroy(&pCollector->dlw);
  dataBufferDestroy(&pCollector->b);
  SCRAMBLE(pCollector);
  sqlite3_free(pCollector);
}


/* Copy the doclist data of iType in pData/nData into *out, trimming
** unnecessary data as we go.  Only columns matching iColumn are
** copied, all columns copied if iColumn is -1.  Elements with no
** matching columns are dropped.  The output is an iOutType doclist.
*/
/* NOTE(shess) This code is only valid after all doclists are merged.
** If this is run before merges, then doclist items which represent
** deletion will be trimmed, and will thus not effect a deletion
** during the merge.
*/
static void docListTrim(DocListType iType, const char *pData, int nData,
                        int iColumn, DocListType iOutType, DataBuffer *out){
  DLReader dlReader;
  DLWriter dlWriter;

  assert( iOutType<=iType );

  dlrInit(&dlReader, iType, pData, nData);
  dlwInit(&dlWriter, iOutType, out);

  while( !dlrAtEnd(&dlReader) ){
    PLReader plReader;
    PLWriter plWriter;
    int match = 0;

    plrInit(&plReader, &dlReader);

    while( !plrAtEnd(&plReader) ){
      if( iColumn==-1 || plrColumn(&plReader)==iColumn ){
        if( !match ){
          plwInit(&plWriter, &dlWriter, dlrDocid(&dlReader));
          match = 1;
        }
        plwAdd(&plWriter, plrColumn(&plReader), plrPosition(&plReader),
               plrStartOffset(&plReader), plrEndOffset(&plReader));
      }
      plrStep(&plReader);
    }
    if( match ){
      plwTerminate(&plWriter);
      plwDestroy(&plWriter);
    }

    plrDestroy(&plReader);
    dlrStep(&dlReader);
  }
  dlwDestroy(&dlWriter);
  dlrDestroy(&dlReader);
}

/* Used by docListMerge() to keep doclists in the ascending order by
** docid, then ascending order by age (so the newest comes first).
*/
typedef struct OrderedDLReader {
  DLReader *pReader;

  /* TODO(shess) If we assume that docListMerge pReaders is ordered by
  ** age (which we do), then we could use pReader comparisons to break
  ** ties.
  */
  int idx;
} OrderedDLReader;

/* Order eof to end, then by docid asc, idx desc. */
static int orderedDLReaderCmp(OrderedDLReader *r1, OrderedDLReader *r2){
  if( dlrAtEnd(r1->pReader) ){
    if( dlrAtEnd(r2->pReader) ) return 0;  /* Both atEnd(). */
    return 1;                              /* Only r1 atEnd(). */
  }
  if( dlrAtEnd(r2->pReader) ) return -1;   /* Only r2 atEnd(). */

  if( dlrDocid(r1->pReader)<dlrDocid(r2->pReader) ) return -1;
  if( dlrDocid(r1->pReader)>dlrDocid(r2->pReader) ) return 1;

  /* Descending on idx. */
  return r2->idx-r1->idx;
}

/* Bubble p[0] to appropriate place in p[1..n-1].  Assumes that
** p[1..n-1] is already sorted.
*/
/* TODO(shess) Is this frequent enough to warrant a binary search?
** Before implementing that, instrument the code to check.  In most
** current usage, I expect that p[0] will be less than p[1] a very
** high proportion of the time.
*/
static void orderedDLReaderReorder(OrderedDLReader *p, int n){
  while( n>1 && orderedDLReaderCmp(p, p+1)>0 ){
    OrderedDLReader tmp = p[0];
    p[0] = p[1];
    p[1] = tmp;
    n--;
    p++;
  }
}

/* Given an array of doclist readers, merge their doclist elements
** into out in sorted order (by docid), dropping elements from older
** readers when there is a duplicate docid.  pReaders is assumed to be
** ordered by age, oldest first.
*/
/* TODO(shess) nReaders must be <= MERGE_COUNT.  This should probably
** be fixed.
*/
static void docListMerge(DataBuffer *out,
                         DLReader *pReaders, int nReaders){
  OrderedDLReader readers[MERGE_COUNT];
  DLWriter writer;
  int i, n;
  const char *pStart = 0;
  int nStart = 0;
  sqlite_int64 iFirstDocid = 0, iLastDocid = 0;

  assert( nReaders>0 );
  if( nReaders==1 ){
    dataBufferAppend(out, dlrDocData(pReaders), dlrAllDataBytes(pReaders));
    return;
  }

  assert( nReaders<=MERGE_COUNT );
  n = 0;
  for(i=0; i<nReaders; i++){
    assert( pReaders[i].iType==pReaders[0].iType );
    readers[i].pReader = pReaders+i;
    readers[i].idx = i;
    n += dlrAllDataBytes(&pReaders[i]);
  }
  /* Conservatively size output to sum of inputs.  Output should end
  ** up strictly smaller than input.
  */
  dataBufferExpand(out, n);

  /* Get the readers into sorted order. */
  while( i-->0 ){
    orderedDLReaderReorder(readers+i, nReaders-i);
  }

  dlwInit(&writer, pReaders[0].iType, out);
  while( !dlrAtEnd(readers[0].pReader) ){
    sqlite_int64 iDocid = dlrDocid(readers[0].pReader);

    /* If this is a continuation of the current buffer to copy, extend
    ** that buffer.  memcpy() seems to be more efficient if it has a
    ** lots of data to copy.
    */
    if( dlrDocData(readers[0].pReader)==pStart+nStart ){
      nStart += dlrDocDataBytes(readers[0].pReader);
    }else{
      if( pStart!=0 ){
        dlwAppend(&writer, pStart, nStart, iFirstDocid, iLastDocid);
      }
      pStart = dlrDocData(readers[0].pReader);
      nStart = dlrDocDataBytes(readers[0].pReader);
      iFirstDocid = iDocid;
    }
    iLastDocid = iDocid;
    dlrStep(readers[0].pReader);

    /* Drop all of the older elements with the same docid. */
    for(i=1; i<nReaders &&
             !dlrAtEnd(readers[i].pReader) &&
             dlrDocid(readers[i].pReader)==iDocid; i++){
      dlrStep(readers[i].pReader);
    }

    /* Get the readers back into order. */
    while( i-->0 ){
      orderedDLReaderReorder(readers+i, nReaders-i);
    }
  }

  /* Copy over any remaining elements. */
  if( nStart>0 ) dlwAppend(&writer, pStart, nStart, iFirstDocid, iLastDocid);
  dlwDestroy(&writer);
}

/* Helper function for posListUnion().  Compares the current position
** between left and right, returning as standard C idiom of <0 if
** left<right, >0 if left>right, and 0 if left==right.  "End" always
** compares greater.
*/
static int posListCmp(PLReader *pLeft, PLReader *pRight){
  assert( pLeft->iType==pRight->iType );
  if( pLeft->iType==DL_DOCIDS ) return 0;

  if( plrAtEnd(pLeft) ) return plrAtEnd(pRight) ? 0 : 1;
  if( plrAtEnd(pRight) ) return -1;

  if( plrColumn(pLeft)<plrColumn(pRight) ) return -1;
  if( plrColumn(pLeft)>plrColumn(pRight) ) return 1;

  if( plrPosition(pLeft)<plrPosition(pRight) ) return -1;
  if( plrPosition(pLeft)>plrPosition(pRight) ) return 1;
  if( pLeft->iType==DL_POSITIONS ) return 0;

  if( plrStartOffset(pLeft)<plrStartOffset(pRight) ) return -1;
  if( plrStartOffset(pLeft)>plrStartOffset(pRight) ) return 1;

  if( plrEndOffset(pLeft)<plrEndOffset(pRight) ) return -1;
  if( plrEndOffset(pLeft)>plrEndOffset(pRight) ) return 1;

  return 0;
}

/* Write the union of position lists in pLeft and pRight to pOut.
** "Union" in this case meaning "All unique position tuples".  Should
** work with any doclist type, though both inputs and the output
** should be the same type.
*/
static void posListUnion(DLReader *pLeft, DLReader *pRight, DLWriter *pOut){
  PLReader left, right;
  PLWriter writer;

  assert( dlrDocid(pLeft)==dlrDocid(pRight) );
  assert( pLeft->iType==pRight->iType );
  assert( pLeft->iType==pOut->iType );

  plrInit(&left, pLeft);
  plrInit(&right, pRight);
  plwInit(&writer, pOut, dlrDocid(pLeft));

  while( !plrAtEnd(&left) || !plrAtEnd(&right) ){
    int c = posListCmp(&left, &right);
    if( c<0 ){
      plwCopy(&writer, &left);
      plrStep(&left);
    }else if( c>0 ){
      plwCopy(&writer, &right);
      plrStep(&right);
    }else{
      plwCopy(&writer, &left);
      plrStep(&left);
      plrStep(&right);
    }
  }

  plwTerminate(&writer);
  plwDestroy(&writer);
  plrDestroy(&left);
  plrDestroy(&right);
}

/* Write the union of doclists in pLeft and pRight to pOut.  For
** docids in common between the inputs, the union of the position
** lists is written.  Inputs and outputs are always type DL_DEFAULT.
*/
static void docListUnion(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 ){
    if( nRight!=0) dataBufferAppend(pOut, pRight, nRight);
    return;
  }
  if( nRight==0 ){
    dataBufferAppend(pOut, pLeft, nLeft);
    return;
  }

  dlrInit(&left, DL_DEFAULT, pLeft, nLeft);
  dlrInit(&right, DL_DEFAULT, pRight, nRight);
  dlwInit(&writer, DL_DEFAULT, pOut);

  while( !dlrAtEnd(&left) || !dlrAtEnd(&right) ){
    if( dlrAtEnd(&right) ){
      dlwCopy(&writer, &left);
      dlrStep(&left);
    }else if( dlrAtEnd(&left) ){
      dlwCopy(&writer, &right);
      dlrStep(&right);
    }else if( dlrDocid(&left)<dlrDocid(&right) ){
      dlwCopy(&writer, &left);
      dlrStep(&left);
    }else if( dlrDocid(&left)>dlrDocid(&right) ){
      dlwCopy(&writer, &right);
      dlrStep(&right);
    }else{
      posListUnion(&left, &right, &writer);
      dlrStep(&left);
      dlrStep(&right);
    }
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

/* 
** This function is used as part of the implementation of phrase and
** NEAR matching.
**
** pLeft and pRight are DLReaders positioned to the same docid in
** lists of type DL_POSITION. This function writes an entry to the
** DLWriter pOut for each position in pRight that is less than
** (nNear+1) greater (but not equal to or smaller) than a position 
** in pLeft. For example, if nNear is 0, and the positions contained
** by pLeft and pRight are:
**
**    pLeft:  5 10 15 20
**    pRight: 6  9 17 21
**
** then the docid is added to pOut. If pOut is of type DL_POSITIONS,
** then a positionids "6" and "21" are also added to pOut.
**
** If boolean argument isSaveLeft is true, then positionids are copied
** from pLeft instead of pRight. In the example above, the positions "5"
** and "20" would be added instead of "6" and "21".


*/
static void posListPhraseMerge(
  DLReader *pLeft, 
  DLReader *pRight,
  int nNear,
  int isSaveLeft,
  DLWriter *pOut
){
  PLReader left, right;
  PLWriter writer;
  int match = 0;

  assert( dlrDocid(pLeft)==dlrDocid(pRight) );
  assert( pOut->iType!=DL_POSITIONS_OFFSETS );

  plrInit(&left, pLeft);
  plrInit(&right, pRight);

  while( !plrAtEnd(&left) && !plrAtEnd(&right) ){
    if( plrColumn(&left)<plrColumn(&right) ){
      plrStep(&left);
    }else if( plrColumn(&left)>plrColumn(&right) ){
      plrStep(&right);
    }else if( plrPosition(&left)>=plrPosition(&right) ){
      plrStep(&right);
    }else{
      if( (plrPosition(&right)-plrPosition(&left))<=(nNear+1) ){
        if( !match ){
          plwInit(&writer, pOut, dlrDocid(pLeft));
          match = 1;
        }
        if( !isSaveLeft ){
          plwAdd(&writer, plrColumn(&right), plrPosition(&right), 0, 0);
        }else{
          plwAdd(&writer, plrColumn(&left), plrPosition(&left), 0, 0);
        }
        plrStep(&right);
      }else{
        plrStep(&left);
      }
    }
  }

  if( match ){
    plwTerminate(&writer);
    plwDestroy(&writer);
  }

  plrDestroy(&left);
  plrDestroy(&right);
}

/*
** Compare the values pointed to by the PLReaders passed as arguments. 
** Return -1 if the value pointed to by pLeft is considered less than
** the value pointed to by pRight, +1 if it is considered greater
** than it, or 0 if it is equal. i.e.
**
**     (*pLeft - *pRight)
**
** A PLReader that is in the EOF condition is considered greater than
** any other. If neither argument is in EOF state, the return value of
** plrColumn() is used. If the plrColumn() values are equal, the
** comparison is on the basis of plrPosition().
*/
static int plrCompare(PLReader *pLeft, PLReader *pRight){
  assert(!plrAtEnd(pLeft) || !plrAtEnd(pRight));

  if( plrAtEnd(pRight) || plrAtEnd(pLeft) ){
    return (plrAtEnd(pRight) ? -1 : 1);
  }
  if( plrColumn(pLeft)!=plrColumn(pRight) ){
    return ((plrColumn(pLeft)<plrColumn(pRight)) ? -1 : 1);
  }
  if( plrPosition(pLeft)!=plrPosition(pRight) ){
    return ((plrPosition(pLeft)<plrPosition(pRight)) ? -1 : 1);
  }
  return 0;
}

/* We have two doclists with positions:  pLeft and pRight. Depending
** on the value of the nNear parameter, perform either a phrase
** intersection (if nNear==0) or a NEAR intersection (if nNear>0)
** and write the results into pOut.
**
** A phrase intersection means that two documents only match
** if pLeft.iPos+1==pRight.iPos.
**
** A NEAR intersection means that two documents only match if 
** (abs(pLeft.iPos-pRight.iPos)<nNear).
**
** If a NEAR intersection is requested, then the nPhrase argument should
** be passed the number of tokens in the two operands to the NEAR operator
** combined. For example:
**
**       Query syntax               nPhrase
**      ------------------------------------
**       "A B C" NEAR "D E"         5
**       A NEAR B                   2
**
** iType controls the type of data written to pOut.  If iType is
** DL_POSITIONS, the positions are those from pRight.
*/
static void docListPhraseMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  int nNear,            /* 0 for a phrase merge, non-zero for a NEAR merge */
  int nPhrase,          /* Number of tokens in left+right operands to NEAR */
  DocListType iType,    /* Type of doclist to write to pOut */
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 || nRight==0 ) return;

  assert( iType!=DL_POSITIONS_OFFSETS );

  dlrInit(&left, DL_POSITIONS, pLeft, nLeft);
  dlrInit(&right, DL_POSITIONS, pRight, nRight);
  dlwInit(&writer, iType, pOut);

  while( !dlrAtEnd(&left) && !dlrAtEnd(&right) ){
    if( dlrDocid(&left)<dlrDocid(&right) ){
      dlrStep(&left);
    }else if( dlrDocid(&right)<dlrDocid(&left) ){
      dlrStep(&right);
    }else{
      if( nNear==0 ){
        posListPhraseMerge(&left, &right, 0, 0, &writer);
      }else{
        /* This case occurs when two terms (simple terms or phrases) are
         * connected by a NEAR operator, span (nNear+1). i.e.
         *
         *     '"terrible company" NEAR widget'
         */
        DataBuffer one = {0, 0, 0};
        DataBuffer two = {0, 0, 0};

        DLWriter dlwriter2;
        DLReader dr1 = {0, 0, 0, 0, 0}; 
        DLReader dr2 = {0, 0, 0, 0, 0};

        dlwInit(&dlwriter2, iType, &one);
        posListPhraseMerge(&right, &left, nNear-3+nPhrase, 1, &dlwriter2);
        dlwInit(&dlwriter2, iType, &two);
        posListPhraseMerge(&left, &right, nNear-1, 0, &dlwriter2);

        if( one.nData) dlrInit(&dr1, iType, one.pData, one.nData);
        if( two.nData) dlrInit(&dr2, iType, two.pData, two.nData);

        if( !dlrAtEnd(&dr1) || !dlrAtEnd(&dr2) ){
          PLReader pr1 = {0};
          PLReader pr2 = {0};

          PLWriter plwriter;
          plwInit(&plwriter, &writer, dlrDocid(dlrAtEnd(&dr1)?&dr2:&dr1));

          if( one.nData ) plrInit(&pr1, &dr1);
          if( two.nData ) plrInit(&pr2, &dr2);
          while( !plrAtEnd(&pr1) || !plrAtEnd(&pr2) ){
            int iCompare = plrCompare(&pr1, &pr2);
            switch( iCompare ){
              case -1:
                plwCopy(&plwriter, &pr1);
                plrStep(&pr1);
                break;
              case 1:
                plwCopy(&plwriter, &pr2);
                plrStep(&pr2);
                break;
              case 0:
                plwCopy(&plwriter, &pr1);
                plrStep(&pr1);
                plrStep(&pr2);
                break;
            }
          }
          plwTerminate(&plwriter);
        }
        dataBufferDestroy(&one);
        dataBufferDestroy(&two);
      }
      dlrStep(&left);
      dlrStep(&right);
    }
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

/* We have two DL_DOCIDS doclists:  pLeft and pRight.
** Write the intersection of these two doclists into pOut as a
** DL_DOCIDS doclist.
*/
static void docListAndMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 || nRight==0 ) return;

  dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
  dlrInit(&right, DL_DOCIDS, pRight, nRight);
  dlwInit(&writer, DL_DOCIDS, pOut);

  while( !dlrAtEnd(&left) && !dlrAtEnd(&right) ){
    if( dlrDocid(&left)<dlrDocid(&right) ){
      dlrStep(&left);
    }else if( dlrDocid(&right)<dlrDocid(&left) ){
      dlrStep(&right);
    }else{
      dlwAdd(&writer, dlrDocid(&left));
      dlrStep(&left);
      dlrStep(&right);
    }
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

/* We have two DL_DOCIDS doclists:  pLeft and pRight.
** Write the union of these two doclists into pOut as a
** DL_DOCIDS doclist.
*/
static void docListOrMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 ){
    if( nRight!=0 ) dataBufferAppend(pOut, pRight, nRight);
    return;
  }
  if( nRight==0 ){
    dataBufferAppend(pOut, pLeft, nLeft);
    return;
  }

  dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
  dlrInit(&right, DL_DOCIDS, pRight, nRight);
  dlwInit(&writer, DL_DOCIDS, pOut);

  while( !dlrAtEnd(&left) || !dlrAtEnd(&right) ){
    if( dlrAtEnd(&right) ){
      dlwAdd(&writer, dlrDocid(&left));
      dlrStep(&left);
    }else if( dlrAtEnd(&left) ){
      dlwAdd(&writer, dlrDocid(&right));
      dlrStep(&right);
    }else if( dlrDocid(&left)<dlrDocid(&right) ){
      dlwAdd(&writer, dlrDocid(&left));
      dlrStep(&left);
    }else if( dlrDocid(&right)<dlrDocid(&left) ){
      dlwAdd(&writer, dlrDocid(&right));
      dlrStep(&right);
    }else{
      dlwAdd(&writer, dlrDocid(&left));
      dlrStep(&left);
      dlrStep(&right);
    }
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

/* We have two DL_DOCIDS doclists:  pLeft and pRight.
** Write into pOut as DL_DOCIDS doclist containing all documents that
** occur in pLeft but not in pRight.
*/
static void docListExceptMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 ) return;
  if( nRight==0 ){
    dataBufferAppend(pOut, pLeft, nLeft);
    return;
  }

  dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
  dlrInit(&right, DL_DOCIDS, pRight, nRight);
  dlwInit(&writer, DL_DOCIDS, pOut);

  while( !dlrAtEnd(&left) ){
    while( !dlrAtEnd(&right) && dlrDocid(&right)<dlrDocid(&left) ){
      dlrStep(&right);
    }
    if( dlrAtEnd(&right) || dlrDocid(&left)<dlrDocid(&right) ){
      dlwAdd(&writer, dlrDocid(&left));
    }
    dlrStep(&left);
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

static char *string_dup_n(const char *s, int n){
  char *str = sqlite3_malloc(n + 1);
  memcpy(str, s, n);
  str[n] = '\0';
  return str;
}

/* Duplicate a string; the caller must free() the returned string.
 * (We don't use strdup() since it is not part of the standard C library and
 * may not be available everywhere.) */
static char *string_dup(const char *s){
  return string_dup_n(s, strlen(s));
}

/* Format a string, replacing each occurrence of the % character with
 * zDb.zName.  This may be more convenient than sqlite_mprintf()
 * when one string is used repeatedly in a format string.
 * The caller must free() the returned string. */
static char *string_format(const char *zFormat,
                           const char *zDb, const char *zName){
  const char *p;
  size_t len = 0;
  size_t nDb = strlen(zDb);
  size_t nName = strlen(zName);
  size_t nFullTableName = nDb+1+nName;
  char *result;
  char *r;

  /* first compute length needed */
  for(p = zFormat ; *p ; ++p){
    len += (*p=='%' ? nFullTableName : 1);
  }
  len += 1;  /* for null terminator */

  r = result = sqlite3_malloc(len);
  for(p = zFormat; *p; ++p){
    if( *p=='%' ){
      memcpy(r, zDb, nDb);
      r += nDb;
      *r++ = '.';
      memcpy(r, zName, nName);
      r += nName;
    } else {
      *r++ = *p;
    }
  }
  *r++ = '\0';
  assert( r == result + len );
  return result;
}

static int sql_exec(sqlite3 *db, const char *zDb, const char *zName,
                    const char *zFormat){
  char *zCommand = string_format(zFormat, zDb, zName);
  int rc;
  FTSTRACE(("FTS3 sql: %s\n", zCommand));
  rc = sqlite3_exec(db, zCommand, NULL, 0, NULL);
  sqlite3_free(zCommand);
  return rc;
}

static int sql_prepare(sqlite3 *db, const char *zDb, const char *zName,
                       sqlite3_stmt **ppStmt, const char *zFormat){
  char *zCommand = string_format(zFormat, zDb, zName);
  int rc;
  FTSTRACE(("FTS3 prepare: %s\n", zCommand));
  rc = sqlite3_prepare_v2(db, zCommand, -1, ppStmt, NULL);
  sqlite3_free(zCommand);
  return rc;
}

/* end utility functions */

/* Forward reference */
typedef struct fulltext_vtab fulltext_vtab;

/*
** An instance of the following structure keeps track of generated
** matching-word offset information and snippets.
*/
typedef struct Snippet {
  int nMatch;     /* Total number of matches */
  int nAlloc;     /* Space allocated for aMatch[] */
  struct snippetMatch { /* One entry for each matching term */
    char snStatus;       /* Status flag for use while constructing snippets */
    short int iCol;      /* The column that contains the match */
    short int iTerm;     /* The index in Query.pTerms[] of the matching term */
    int iToken;          /* The index of the matching document token */
    short int nByte;     /* Number of bytes in the term */
    int iStart;          /* The offset to the first character of the term */
  } *aMatch;      /* Points to space obtained from malloc */
  char *zOffset;  /* Text rendering of aMatch[] */
  int nOffset;    /* strlen(zOffset) */
  char *zSnippet; /* Snippet text */
  int nSnippet;   /* strlen(zSnippet) */
} Snippet;


typedef enum QueryType {
  QUERY_GENERIC,   /* table scan */
  QUERY_DOCID,     /* lookup by docid */
  QUERY_FULLTEXT   /* QUERY_FULLTEXT + [i] is a full-text search for column i*/
} QueryType;

typedef enum fulltext_statement {
  CONTENT_INSERT_STMT,
  CONTENT_SELECT_STMT,
  CONTENT_UPDATE_STMT,
  CONTENT_DELETE_STMT,
  CONTENT_EXISTS_STMT,

  BLOCK_INSERT_STMT,
  BLOCK_SELECT_STMT,
  BLOCK_DELETE_STMT,
  BLOCK_DELETE_ALL_STMT,

  SEGDIR_MAX_INDEX_STMT,
  SEGDIR_SET_STMT,
  SEGDIR_SELECT_LEVEL_STMT,
  SEGDIR_SPAN_STMT,
  SEGDIR_DELETE_STMT,
  SEGDIR_SELECT_SEGMENT_STMT,
  SEGDIR_SELECT_ALL_STMT,
  SEGDIR_DELETE_ALL_STMT,
  SEGDIR_COUNT_STMT,

  MAX_STMT                     /* Always at end! */
} fulltext_statement;

/* These must exactly match the enum above. */
/* TODO(shess): Is there some risk that a statement will be used in two
** cursors at once, e.g.  if a query joins a virtual table to itself?
** If so perhaps we should move some of these to the cursor object.
*/
static const char *const fulltext_zStatement[MAX_STMT] = {
  /* CONTENT_INSERT */ NULL,  /* generated in contentInsertStatement() */
  /* CONTENT_SELECT */ NULL,  /* generated in contentSelectStatement() */
  /* CONTENT_UPDATE */ NULL,  /* generated in contentUpdateStatement() */
  /* CONTENT_DELETE */ "delete from %_content where docid = ?",
  /* CONTENT_EXISTS */ "select docid from %_content limit 1",

  /* BLOCK_INSERT */
  "insert into %_segments (blockid, block) values (null, ?)",
  /* BLOCK_SELECT */ "select block from %_segments where blockid = ?",
  /* BLOCK_DELETE */ "delete from %_segments where blockid between ? and ?",
  /* BLOCK_DELETE_ALL */ "delete from %_segments",

  /* SEGDIR_MAX_INDEX */ "select max(idx) from %_segdir where level = ?",
  /* SEGDIR_SET */ "insert into %_segdir values (?, ?, ?, ?, ?, ?)",
  /* SEGDIR_SELECT_LEVEL */
  "select start_block, leaves_end_block, root from %_segdir "
  " where level = ? order by idx",
  /* SEGDIR_SPAN */
  "select min(start_block), max(end_block) from %_segdir "
  " where level = ? and start_block <> 0",
  /* SEGDIR_DELETE */ "delete from %_segdir where level = ?",

  /* NOTE(shess): The first three results of the following two
  ** statements must match.
  */
  /* SEGDIR_SELECT_SEGMENT */
  "select start_block, leaves_end_block, root from %_segdir "
  " where level = ? and idx = ?",
  /* SEGDIR_SELECT_ALL */
  "select start_block, leaves_end_block, root from %_segdir "
  " order by level desc, idx asc",
  /* SEGDIR_DELETE_ALL */ "delete from %_segdir",
  /* SEGDIR_COUNT */ "select count(*), ifnull(max(level),0) from %_segdir",
};

/*
** A connection to a fulltext index is an instance of the following
** structure.  The xCreate and xConnect methods create an instance
** of this structure and xDestroy and xDisconnect free that instance.
** All other methods receive a pointer to the structure as one of their
** arguments.
*/
struct fulltext_vtab {
  sqlite3_vtab base;               /* Base class used by SQLite core */
  sqlite3 *db;                     /* The database connection */
  const char *zDb;                 /* logical database name */
  const char *zName;               /* virtual table name */
  int nColumn;                     /* number of columns in virtual table */
  char **azColumn;                 /* column names.  malloced */
  char **azContentColumn;          /* column names in content table; malloced */
  sqlite3_tokenizer *pTokenizer;   /* tokenizer for inserts and queries */

  /* Precompiled statements which we keep as long as the table is
  ** open.
  */
  sqlite3_stmt *pFulltextStatements[MAX_STMT];

  /* Precompiled statements used for segment merges.  We run a
  ** separate select across the leaf level of each tree being merged.
  */
  sqlite3_stmt *pLeafSelectStmts[MERGE_COUNT];
  /* The statement used to prepare pLeafSelectStmts. */
#define LEAF_SELECT \
  "select block from %_segments where blockid between ? and ? order by blockid"

  /* These buffer pending index updates during transactions.
  ** nPendingData estimates the memory size of the pending data.  It
  ** doesn't include the hash-bucket overhead, nor any malloc
  ** overhead.  When nPendingData exceeds kPendingThreshold, the
  ** buffer is flushed even before the transaction closes.
  ** pendingTerms stores the data, and is only valid when nPendingData
  ** is >=0 (nPendingData<0 means pendingTerms has not been
  ** initialized).  iPrevDocid is the last docid written, used to make
  ** certain we're inserting in sorted order.
  */
  int nPendingData;
#define kPendingThreshold (1*1024*1024)
  sqlite_int64 iPrevDocid;
  fts3Hash pendingTerms;
};

/*
** When the core wants to do a query, it create a cursor using a
** call to xOpen.  This structure is an instance of a cursor.  It
** is destroyed by xClose.
*/
typedef struct fulltext_cursor {
  sqlite3_vtab_cursor base;        /* Base class used by SQLite core */
  QueryType iCursorType;           /* Copy of sqlite3_index_info.idxNum */
  sqlite3_stmt *pStmt;             /* Prepared statement in use by the cursor */
  int eof;                         /* True if at End Of Results */
  Fts3Expr *pExpr;                 /* Parsed MATCH query string */
  Snippet snippet;                 /* Cached snippet for the current row */
  int iColumn;                     /* Column being searched */
  DataBuffer result;               /* Doclist results from fulltextQuery */
  DLReader reader;                 /* Result reader if result not empty */
} fulltext_cursor;

static fulltext_vtab *cursor_vtab(fulltext_cursor *c){
  return (fulltext_vtab *) c->base.pVtab;
}

static const sqlite3_module fts3Module;   /* forward declaration */

/* Return a dynamically generated statement of the form
 *   insert into %_content (docid, ...) values (?, ...)
 */
static const char *contentInsertStatement(fulltext_vtab *v){
  StringBuffer sb;

  int i;

  initStringBuffer(&sb);
  append(&sb, "insert into %_content (docid, ");
  appendList(&sb, v->nColumn, v->azContentColumn);
  append(&sb, ") values (?");
  for(i=0; i<v->nColumn; ++i)
    append(&sb, ", ?");
  append(&sb, ")");
  return stringBufferData(&sb);
}

/* Return a dynamically generated statement of the form
 *   select <content columns> from %_content where docid = ?
 */
static const char *contentSelectStatement(fulltext_vtab *v){
  StringBuffer sb;
  initStringBuffer(&sb);
  append(&sb, "SELECT ");
  appendList(&sb, v->nColumn, v->azContentColumn);
  append(&sb, " FROM %_content WHERE docid = ?");
  return stringBufferData(&sb);
}

/* Return a dynamically generated statement of the form
 *   update %_content set [col_0] = ?, [col_1] = ?, ...
 *                    where docid = ?
 */
static const char *contentUpdateStatement(fulltext_vtab *v){
  StringBuffer sb;
  int i;

  initStringBuffer(&sb);
  append(&sb, "update %_content set ");
  for(i=0; i<v->nColumn; ++i) {
    if( i>0 ){
      append(&sb, ", ");
    }
    append(&sb, v->azContentColumn[i]);
    append(&sb, " = ?");
  }
  append(&sb, " where docid = ?");
  return stringBufferData(&sb);
}

/* Puts a freshly-prepared statement determined by iStmt in *ppStmt.
** If the indicated statement has never been prepared, it is prepared
** and cached, otherwise the cached version is reset.
*/
static int sql_get_statement(fulltext_vtab *v, fulltext_statement iStmt,
                             sqlite3_stmt **ppStmt){
  assert( iStmt<MAX_STMT );
  if( v->pFulltextStatements[iStmt]==NULL ){
    const char *zStmt;
    int rc;
    switch( iStmt ){
      case CONTENT_INSERT_STMT:
        zStmt = contentInsertStatement(v); break;
      case CONTENT_SELECT_STMT:
        zStmt = contentSelectStatement(v); break;
      case CONTENT_UPDATE_STMT:
        zStmt = contentUpdateStatement(v); break;
      default:
        zStmt = fulltext_zStatement[iStmt];
    }
    rc = sql_prepare(v->db, v->zDb, v->zName, &v->pFulltextStatements[iStmt],
                         zStmt);
    if( zStmt != fulltext_zStatement[iStmt]) sqlite3_free((void *) zStmt);
    if( rc!=SQLITE_OK ) return rc;
  } else {
    int rc = sqlite3_reset(v->pFulltextStatements[iStmt]);
    if( rc!=SQLITE_OK ) return rc;
  }

  *ppStmt = v->pFulltextStatements[iStmt];
  return SQLITE_OK;
}

/* Like sqlite3_step(), but convert SQLITE_DONE to SQLITE_OK and
** SQLITE_ROW to SQLITE_ERROR.  Useful for statements like UPDATE,
** where we expect no results.
*/
static int sql_single_step(sqlite3_stmt *s){
  int rc = sqlite3_step(s);
  return (rc==SQLITE_DONE) ? SQLITE_OK : rc;
}

/* Like sql_get_statement(), but for special replicated LEAF_SELECT
** statements.  idx -1 is a special case for an uncached version of
** the statement (used in the optimize implementation).
*/
/* TODO(shess) Write version for generic statements and then share
** that between the cached-statement functions.
*/
static int sql_get_leaf_statement(fulltext_vtab *v, int idx,
                                  sqlite3_stmt **ppStmt){
  assert( idx>=-1 && idx<MERGE_COUNT );
  if( idx==-1 ){
    return sql_prepare(v->db, v->zDb, v->zName, ppStmt, LEAF_SELECT);
  }else if( v->pLeafSelectStmts[idx]==NULL ){
    int rc = sql_prepare(v->db, v->zDb, v->zName, &v->pLeafSelectStmts[idx],
                         LEAF_SELECT);
    if( rc!=SQLITE_OK ) return rc;
  }else{
    int rc = sqlite3_reset(v->pLeafSelectStmts[idx]);
    if( rc!=SQLITE_OK ) return rc;
  }

  *ppStmt = v->pLeafSelectStmts[idx];
  return SQLITE_OK;
}

/* insert into %_content (docid, ...) values ([docid], [pValues])
** If the docid contains SQL NULL, then a unique docid will be
** generated.
*/
static int content_insert(fulltext_vtab *v, sqlite3_value *docid,
                          sqlite3_value **pValues){
  sqlite3_stmt *s;
  int i;
  int rc = sql_get_statement(v, CONTENT_INSERT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_value(s, 1, docid);
  if( rc!=SQLITE_OK ) return rc;

  for(i=0; i<v->nColumn; ++i){
    rc = sqlite3_bind_value(s, 2+i, pValues[i]);
    if( rc!=SQLITE_OK ) return rc;
  }

  return sql_single_step(s);
}

/* update %_content set col0 = pValues[0], col1 = pValues[1], ...
 *                  where docid = [iDocid] */
static int content_update(fulltext_vtab *v, sqlite3_value **pValues,
                          sqlite_int64 iDocid){
  sqlite3_stmt *s;
  int i;
  int rc = sql_get_statement(v, CONTENT_UPDATE_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  for(i=0; i<v->nColumn; ++i){
    rc = sqlite3_bind_value(s, 1+i, pValues[i]);
    if( rc!=SQLITE_OK ) return rc;
  }

  rc = sqlite3_bind_int64(s, 1+v->nColumn, iDocid);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step(s);
}

static void freeStringArray(int nString, const char **pString){
  int i;

  for (i=0 ; i < nString ; ++i) {
    if( pString[i]!=NULL ) sqlite3_free((void *) pString[i]);
  }
  sqlite3_free((void *) pString);
}

/* select * from %_content where docid = [iDocid]
 * The caller must delete the returned array and all strings in it.
 * null fields will be NULL in the returned array.
 *
 * TODO: Perhaps we should return pointer/length strings here for consistency
 * with other code which uses pointer/length. */
static int content_select(fulltext_vtab *v, sqlite_int64 iDocid,
                          const char ***pValues){
  sqlite3_stmt *s;
  const char **values;
  int i;
  int rc;

  *pValues = NULL;

  rc = sql_get_statement(v, CONTENT_SELECT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iDocid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_step(s);
  if( rc!=SQLITE_ROW ) return rc;

  values = (const char **) sqlite3_malloc(v->nColumn * sizeof(const char *));
  for(i=0; i<v->nColumn; ++i){
    if( sqlite3_column_type(s, i)==SQLITE_NULL ){
      values[i] = NULL;
    }else{
      values[i] = string_dup((char*)sqlite3_column_text(s, i));
    }
  }

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_DONE ){
    *pValues = values;
    return SQLITE_OK;
  }

  freeStringArray(v->nColumn, values);
  return rc;
}

/* delete from %_content where docid = [iDocid ] */
static int content_delete(fulltext_vtab *v, sqlite_int64 iDocid){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, CONTENT_DELETE_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iDocid);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step(s);
}

/* Returns SQLITE_ROW if any rows exist in %_content, SQLITE_DONE if
** no rows exist, and any error in case of failure.
*/
static int content_exists(fulltext_vtab *v){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, CONTENT_EXISTS_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_step(s);
  if( rc!=SQLITE_ROW ) return rc;

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_DONE ) return SQLITE_ROW;
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  return rc;
}

/* insert into %_segments values ([pData])
**   returns assigned blockid in *piBlockid
*/
static int block_insert(fulltext_vtab *v, const char *pData, int nData,
                        sqlite_int64 *piBlockid){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, BLOCK_INSERT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_blob(s, 1, pData, nData, SQLITE_STATIC);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_step(s);
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  if( rc!=SQLITE_DONE ) return rc;

  /* blockid column is an alias for rowid. */
  *piBlockid = sqlite3_last_insert_rowid(v->db);
  return SQLITE_OK;
}

/* delete from %_segments
**   where blockid between [iStartBlockid] and [iEndBlockid]
**
** Deletes the range of blocks, inclusive, used to delete the blocks
** which form a segment.
*/
static int block_delete(fulltext_vtab *v,
                        sqlite_int64 iStartBlockid, sqlite_int64 iEndBlockid){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, BLOCK_DELETE_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iStartBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 2, iEndBlockid);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step(s);
}

/* Returns SQLITE_ROW with *pidx set to the maximum segment idx found
** at iLevel.  Returns SQLITE_DONE if there are no segments at
** iLevel.  Otherwise returns an error.
*/
static int segdir_max_index(fulltext_vtab *v, int iLevel, int *pidx){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_MAX_INDEX_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_step(s);
  /* Should always get at least one row due to how max() works. */
  if( rc==SQLITE_DONE ) return SQLITE_DONE;
  if( rc!=SQLITE_ROW ) return rc;

  /* NULL means that there were no inputs to max(). */
  if( SQLITE_NULL==sqlite3_column_type(s, 0) ){
    rc = sqlite3_step(s);
    if( rc==SQLITE_ROW ) return SQLITE_ERROR;
    return rc;
  }

  *pidx = sqlite3_column_int(s, 0);

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  if( rc!=SQLITE_DONE ) return rc;
  return SQLITE_ROW;
}

/* insert into %_segdir values (
**   [iLevel], [idx],
**   [iStartBlockid], [iLeavesEndBlockid], [iEndBlockid],
**   [pRootData]
** )
*/
static int segdir_set(fulltext_vtab *v, int iLevel, int idx,
                      sqlite_int64 iStartBlockid,
                      sqlite_int64 iLeavesEndBlockid,
                      sqlite_int64 iEndBlockid,
                      const char *pRootData, int nRootData){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_SET_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 2, idx);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 3, iStartBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 4, iLeavesEndBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 5, iEndBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_blob(s, 6, pRootData, nRootData, SQLITE_STATIC);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step(s);
}

/* Queries %_segdir for the block span of the segments in level
** iLevel.  Returns SQLITE_DONE if there are no blocks for iLevel,
** SQLITE_ROW if there are blocks, else an error.
*/
static int segdir_span(fulltext_vtab *v, int iLevel,
                       sqlite_int64 *piStartBlockid,
                       sqlite_int64 *piEndBlockid){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_SPAN_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_step(s);
  if( rc==SQLITE_DONE ) return SQLITE_DONE;  /* Should never happen */
  if( rc!=SQLITE_ROW ) return rc;

  /* This happens if all segments at this level are entirely inline. */
  if( SQLITE_NULL==sqlite3_column_type(s, 0) ){
    /* We expect only one row.  We must execute another sqlite3_step()
     * to complete the iteration; otherwise the table will remain locked. */
    int rc2 = sqlite3_step(s);
    if( rc2==SQLITE_ROW ) return SQLITE_ERROR;
    return rc2;
  }

  *piStartBlockid = sqlite3_column_int64(s, 0);
  *piEndBlockid = sqlite3_column_int64(s, 1);

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  if( rc!=SQLITE_DONE ) return rc;
  return SQLITE_ROW;
}

/* Delete the segment blocks and segment directory records for all
** segments at iLevel.
*/
static int segdir_delete(fulltext_vtab *v, int iLevel){
  sqlite3_stmt *s;
  sqlite_int64 iStartBlockid, iEndBlockid;
  int rc = segdir_span(v, iLevel, &iStartBlockid, &iEndBlockid);
  if( rc!=SQLITE_ROW && rc!=SQLITE_DONE ) return rc;

  if( rc==SQLITE_ROW ){
    rc = block_delete(v, iStartBlockid, iEndBlockid);
    if( rc!=SQLITE_OK ) return rc;
  }

  /* Delete the segment directory itself. */
  rc = sql_get_statement(v, SEGDIR_DELETE_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step(s);
}

/* Delete entire fts index, SQLITE_OK on success, relevant error on
** failure.
*/
static int segdir_delete_all(fulltext_vtab *v){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_DELETE_ALL_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sql_single_step(s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sql_get_statement(v, BLOCK_DELETE_ALL_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step(s);
}

/* Returns SQLITE_OK with *pnSegments set to the number of entries in
** %_segdir and *piMaxLevel set to the highest level which has a
** segment.  Otherwise returns the SQLite error which caused failure.
*/
static int segdir_count(fulltext_vtab *v, int *pnSegments, int *piMaxLevel){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_COUNT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_step(s);
  /* TODO(shess): This case should not be possible?  Should stronger
  ** measures be taken if it happens?
  */
  if( rc==SQLITE_DONE ){
    *pnSegments = 0;
    *piMaxLevel = 0;
    return SQLITE_OK;
  }
  if( rc!=SQLITE_ROW ) return rc;

  *pnSegments = sqlite3_column_int(s, 0);
  *piMaxLevel = sqlite3_column_int(s, 1);

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_DONE ) return SQLITE_OK;
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  return rc;
}

/* TODO(shess) clearPendingTerms() is far down the file because
** writeZeroSegment() is far down the file because LeafWriter is far
** down the file.  Consider refactoring the code to move the non-vtab
** code above the vtab code so that we don't need this forward
** reference.
*/
static int clearPendingTerms(fulltext_vtab *v);

/*
** Free the memory used to contain a fulltext_vtab structure.
*/
static void fulltext_vtab_destroy(fulltext_vtab *v){
  int iStmt, i;

  FTSTRACE(("FTS3 Destroy %p\n", v));
  for( iStmt=0; iStmt<MAX_STMT; iStmt++ ){
    if( v->pFulltextStatements[iStmt]!=NULL ){
      sqlite3_finalize(v->pFulltextStatements[iStmt]);
      v->pFulltextStatements[iStmt] = NULL;
    }
  }

  for( i=0; i<MERGE_COUNT; i++ ){
    if( v->pLeafSelectStmts[i]!=NULL ){
      sqlite3_finalize(v->pLeafSelectStmts[i]);
      v->pLeafSelectStmts[i] = NULL;
    }
  }

  if( v->pTokenizer!=NULL ){
    v->pTokenizer->pModule->xDestroy(v->pTokenizer);
    v->pTokenizer = NULL;
  }

  clearPendingTerms(v);

  sqlite3_free(v->azColumn);
  for(i = 0; i < v->nColumn; ++i) {
    sqlite3_free(v->azContentColumn[i]);
  }
  sqlite3_free(v->azContentColumn);
  sqlite3_free(v);
}

/*
** Token types for parsing the arguments to xConnect or xCreate.
*/
#define TOKEN_EOF         0    /* End of file */
#define TOKEN_SPACE       1    /* Any kind of whitespace */
#define TOKEN_ID          2    /* An identifier */
#define TOKEN_STRING      3    /* A string literal */
#define TOKEN_PUNCT       4    /* A single punctuation character */

/*
** If X is a character that can be used in an identifier then
** ftsIdChar(X) will be true.  Otherwise it is false.
**
** For ASCII, any character with the high-order bit set is
** allowed in an identifier.  For 7-bit characters, 
** isFtsIdChar[X] must be 1.
**
** Ticket #1066.  the SQL standard does not allow '$' in the
** middle of identfiers.  But many SQL implementations do. 
** SQLite will allow '$' in identifiers for compatibility.
** But the feature is undocumented.
*/
static const char isFtsIdChar[] = {
/* x0 x1 x2 x3 x4 x5 x6 x7 x8 x9 xA xB xC xD xE xF */
    0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  /* 2x */
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0,  /* 3x */
    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  /* 4x */
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1,  /* 5x */
    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  /* 6x */
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0,  /* 7x */
};
#define ftsIdChar(C)  (((c=C)&0x80)!=0 || (c>0x1f && isFtsIdChar[c-0x20]))


/*
** Return the length of the token that begins at z[0]. 
** Store the token type in *tokenType before returning.
*/
static int ftsGetToken(const char *z, int *tokenType){
  int i, c;
  switch( *z ){
    case 0: {
      *tokenType = TOKEN_EOF;
      return 0;
    }
    case ' ': case '\t': case '\n': case '\f': case '\r': {
      for(i=1; safe_isspace(z[i]); i++){}
      *tokenType = TOKEN_SPACE;
      return i;
    }
    case '`':
    case '\'':
    case '"': {
      int delim = z[0];
      for(i=1; (c=z[i])!=0; i++){
        if( c==delim ){
          if( z[i+1]==delim ){

            i++;
          }else{
            break;
          }
        }
      }
      *tokenType = TOKEN_STRING;
      return i + (c!=0);
    }
    case '[': {
      for(i=1, c=z[0]; c!=']' && (c=z[i])!=0; i++){}
      *tokenType = TOKEN_ID;
      return i;
    }
    default: {
      if( !ftsIdChar(*z) ){
        break;
      }
      for(i=1; ftsIdChar(z[i]); i++){}
      *tokenType = TOKEN_ID;
      return i;
    }
  }
  *tokenType = TOKEN_PUNCT;
  return 1;
}

/*
** A token extracted from a string is an instance of the following
** structure.
*/
typedef struct FtsToken {
  const char *z;       /* Pointer to token text.  Not '\000' terminated */
  short int n;         /* Length of the token text in bytes. */
} FtsToken;

/*
** Given a input string (which is really one of the argv[] parameters
** passed into xConnect or xCreate) split the string up into tokens.
** Return an array of pointers to '\000' terminated strings, one string
** for each non-whitespace token.
**
** The returned array is terminated by a single NULL pointer.
**
** Space to hold the returned array is obtained from a single
** malloc and should be freed by passing the return value to free().
** The individual strings within the token list are all a part of
** the single memory allocation and will all be freed at once.
*/
static char **tokenizeString(const char *z, int *pnToken){
  int nToken = 0;
  FtsToken *aToken = sqlite3_malloc( strlen(z) * sizeof(aToken[0]) );
  int n = 1;
  int e, i;
  int totalSize = 0;
  char **azToken;
  char *zCopy;

  while( n>0 ){
    n = ftsGetToken(z, &e);
    if( e!=TOKEN_SPACE ){
      aToken[nToken].z = z;
      aToken[nToken].n = n;
      nToken++;
      totalSize += n+1;
    }
    z += n;
  }
  azToken = (char**)sqlite3_malloc( nToken*sizeof(char*) + totalSize );
  zCopy = (char*)&azToken[nToken];
  nToken--;
  for(i=0; i<nToken; i++){
    azToken[i] = zCopy;
    n = aToken[i].n;
    memcpy(zCopy, aToken[i].z, n);
    zCopy[n] = 0;
    zCopy += n+1;
  }
  azToken[nToken] = 0;
  sqlite3_free(aToken);
  *pnToken = nToken;
  return azToken;
}

/*
** Convert an SQL-style quoted string into a normal string by removing
** the quote characters.  The conversion is done in-place.  If the
** input does not begin with a quote character, then this routine
** is a no-op.
................................................................................
** Examples:
**
**     "abc"   becomes   abc
**     'xyz'   becomes   xyz
**     [pqr]   becomes   pqr
**     `mno`   becomes   mno
*/
static void dequoteString(char *z){
  int quote;
  int i, j;
  if( z==0 ) return;

  quote = z[0];
  switch( quote ){
    case '\'':  break;
    case '"':   break;
    case '`':   break;                /* For MySQL compatibility */
    case '[':   quote = ']';  break;  /* For MS SqlServer compatibility */
    default:    return;
  }
  for(i=1, j=0; z[i]; i++){
    if( z[i]==quote ){
      if( z[i+1]==quote ){
        z[j++] = quote;
        i++;
      }else{
        z[j++] = 0;
        break;
      }
    }else{
      z[j++] = z[i];
    }
  }
}

/*
** The input azIn is a NULL-terminated list of tokens.  Remove the first
** token and all punctuation tokens.  Remove the quotes from
** around string literal tokens.
**
** Example:
**
**     input:      tokenize chinese ( 'simplifed' , 'mixed' )
**     output:     chinese simplifed mixed
**
** Another example:
**
**     input:      delimiters ( '[' , ']' , '...' )
**     output:     [ ] ...
*/
static void tokenListToIdList(char **azIn){
  int i, j;
  if( azIn ){
    for(i=0, j=-1; azIn[i]; i++){
      if( safe_isalnum(azIn[i][0]) || azIn[i][1] ){
        dequoteString(azIn[i]);
        if( j>=0 ){
          azIn[j] = azIn[i];
        }
        j++;
      }
    }
    azIn[j] = 0;
  }
}


/*
** Find the first alphanumeric token in the string zIn.  Null-terminate
** this token.  Remove any quotation marks.  And return a pointer to
** the result.
*/
static char *firstToken(char *zIn, char **pzTail){
  int n, ttype;
  while(1){
    n = ftsGetToken(zIn, &ttype);
    if( ttype==TOKEN_SPACE ){
      zIn += n;
    }else if( ttype==TOKEN_EOF ){
      *pzTail = zIn;
      return 0;
    }else{
      zIn[n] = 0;
      *pzTail = &zIn[1];
      dequoteString(zIn);
      return zIn;
    }
  }
  /*NOTREACHED*/
}

/* Return true if...
**
**   *  s begins with the string t, ignoring case
**   *  s is longer than t
**   *  The first character of s beyond t is not a alphanumeric
** 
** Ignore leading space in *s.
**
** To put it another way, return true if the first token of
** s[] is t[].
*/
static int startsWith(const char *s, const char *t){
  while( safe_isspace(*s) ){ s++; }
  while( *t ){
    if( safe_tolower(*s++)!=safe_tolower(*t++) ) return 0;
  }
  return *s!='_' && !safe_isalnum(*s);
}

/*
** An instance of this structure defines the "spec" of a
** full text index.  This structure is populated by parseSpec
** and use by fulltextConnect and fulltextCreate.
*/
typedef struct TableSpec {
  const char *zDb;         /* Logical database name */
  const char *zName;       /* Name of the full-text index */
  int nColumn;             /* Number of columns to be indexed */
  char **azColumn;         /* Original names of columns to be indexed */
  char **azContentColumn;  /* Column names for %_content */
  char **azTokenizer;      /* Name of tokenizer and its arguments */
} TableSpec;

/*
** Reclaim all of the memory used by a TableSpec
*/
static void clearTableSpec(TableSpec *p) {
  sqlite3_free(p->azColumn);
  sqlite3_free(p->azContentColumn);
  sqlite3_free(p->azTokenizer);
}

/* Parse a CREATE VIRTUAL TABLE statement, which looks like this:
 *
 * CREATE VIRTUAL TABLE email
 *        USING fts3(subject, body, tokenize mytokenizer(myarg))
 *
 * We return parsed information in a TableSpec structure.
 * 
 */
static int parseSpec(TableSpec *pSpec, int argc, const char *const*argv,
                     char**pzErr){
  int i, n;
  char *z, *zDummy;
  char **azArg;
  const char *zTokenizer = 0;    /* argv[] entry describing the tokenizer */

  assert( argc>=3 );
  /* Current interface:
  ** argv[0] - module name
  ** argv[1] - database name
  ** argv[2] - table name
  ** argv[3..] - columns, optionally followed by tokenizer specification
  **             and snippet delimiters specification.
  */

  /* Make a copy of the complete argv[][] array in a single allocation.
  ** The argv[][] array is read-only and transient.  We can write to the
  ** copy in order to modify things and the copy is persistent.
  */
  CLEAR(pSpec);
  for(i=n=0; i<argc; i++){
    n += strlen(argv[i]) + 1;
  }
  azArg = sqlite3_malloc( sizeof(char*)*argc + n );
  if( azArg==0 ){
    return SQLITE_NOMEM;
  }
  z = (char*)&azArg[argc];
  for(i=0; i<argc; i++){
    azArg[i] = z;
    strcpy(z, argv[i]);
    z += strlen(z)+1;
  }

  /* Identify the column names and the tokenizer and delimiter arguments
  ** in the argv[][] array.
  */
  pSpec->zDb = azArg[1];
  pSpec->zName = azArg[2];
  pSpec->nColumn = 0;
  pSpec->azColumn = azArg;
  zTokenizer = "tokenize simple";
  for(i=3; i<argc; ++i){
    if( startsWith(azArg[i],"tokenize") ){
      zTokenizer = azArg[i];
    }else{
      z = azArg[pSpec->nColumn] = firstToken(azArg[i], &zDummy);
      pSpec->nColumn++;
    }
  }
  if( pSpec->nColumn==0 ){
    azArg[0] = "content";
    pSpec->nColumn = 1;
  }

  /*
  ** Construct the list of content column names.
  **
  ** Each content column name will be of the form cNNAAAA
  ** where NN is the column number and AAAA is the sanitized
  ** column name.  "sanitized" means that special characters are
  ** converted to "_".  The cNN prefix guarantees that all column
  ** names are unique.
  **
  ** The AAAA suffix is not strictly necessary.  It is included
  ** for the convenience of people who might examine the generated
  ** %_content table and wonder what the columns are used for.
  */
  pSpec->azContentColumn = sqlite3_malloc( pSpec->nColumn * sizeof(char *) );
  if( pSpec->azContentColumn==0 ){
    clearTableSpec(pSpec);
    return SQLITE_NOMEM;
  }
  for(i=0; i<pSpec->nColumn; i++){
    char *p;
    pSpec->azContentColumn[i] = sqlite3_mprintf("c%d%s", i, azArg[i]);
    for (p = pSpec->azContentColumn[i]; *p ; ++p) {
      if( !safe_isalnum(*p) ) *p = '_';
    }
  }

  /*
  ** Parse the tokenizer specification string.
  */
  pSpec->azTokenizer = tokenizeString(zTokenizer, &n);
  tokenListToIdList(pSpec->azTokenizer);

  return SQLITE_OK;
}

/*
** Generate a CREATE TABLE statement that describes the schema of
** the virtual table.  Return a pointer to this schema string.
**
** Space is obtained from sqlite3_mprintf() and should be freed
** using sqlite3_free().
*/
static char *fulltextSchema(
  int nColumn,                  /* Number of columns */
  const char *const* azColumn,  /* List of columns */
  const char *zTableName        /* Name of the table */
){
  int i;
  char *zSchema, *zNext;
  const char *zSep = "(";
  zSchema = sqlite3_mprintf("CREATE TABLE x");
  for(i=0; i<nColumn; i++){
    zNext = sqlite3_mprintf("%s%s%Q", zSchema, zSep, azColumn[i]);
    sqlite3_free(zSchema);
    zSchema = zNext;
    zSep = ",";
  }
  zNext = sqlite3_mprintf("%s,%Q HIDDEN", zSchema, zTableName);
  sqlite3_free(zSchema);
  zSchema = zNext;
  zNext = sqlite3_mprintf("%s,docid HIDDEN)", zSchema);
  sqlite3_free(zSchema);
  return zNext;
}

/*
** Build a new sqlite3_vtab structure that will describe the
** fulltext index defined by spec.
*/
static int constructVtab(
  sqlite3 *db,              /* The SQLite database connection */
  fts3Hash *pHash,          /* Hash table containing tokenizers */
  TableSpec *spec,          /* Parsed spec information from parseSpec() */
  sqlite3_vtab **ppVTab,    /* Write the resulting vtab structure here */
  char **pzErr              /* Write any error message here */
){
  int rc;
  int n;
  fulltext_vtab *v = 0;
  const sqlite3_tokenizer_module *m = NULL;
  char *schema;

  char const *zTok;         /* Name of tokenizer to use for this fts table */
  int nTok;                 /* Length of zTok, including nul terminator */

  v = (fulltext_vtab *) sqlite3_malloc(sizeof(fulltext_vtab));
  if( v==0 ) return SQLITE_NOMEM;
  CLEAR(v);
  /* sqlite will initialize v->base */
  v->db = db;
  v->zDb = spec->zDb;       /* Freed when azColumn is freed */
  v->zName = spec->zName;   /* Freed when azColumn is freed */
  v->nColumn = spec->nColumn;
  v->azContentColumn = spec->azContentColumn;
  spec->azContentColumn = 0;
  v->azColumn = spec->azColumn;
  spec->azColumn = 0;

  if( spec->azTokenizer==0 ){
    return SQLITE_NOMEM;
  }

  zTok = spec->azTokenizer[0]; 
  if( !zTok ){
    zTok = "simple";
  }
  nTok = strlen(zTok)+1;

  m = (sqlite3_tokenizer_module *)sqlite3Fts3HashFind(pHash, zTok, nTok);
  if( !m ){
    *pzErr = sqlite3_mprintf("unknown tokenizer: %s", spec->azTokenizer[0]);
    rc = SQLITE_ERROR;
    goto err;
  }

  for(n=0; spec->azTokenizer[n]; n++){}
  if( n ){
    rc = m->xCreate(n-1, (const char*const*)&spec->azTokenizer[1],
                    &v->pTokenizer);
  }else{
    rc = m->xCreate(0, 0, &v->pTokenizer);
  }
  if( rc!=SQLITE_OK ) goto err;
  v->pTokenizer->pModule = m;

  /* TODO: verify the existence of backing tables foo_content, foo_term */

  schema = fulltextSchema(v->nColumn, (const char*const*)v->azColumn,
                          spec->zName);
  rc = sqlite3_declare_vtab(db, schema);
  sqlite3_free(schema);
  if( rc!=SQLITE_OK ) goto err;

  memset(v->pFulltextStatements, 0, sizeof(v->pFulltextStatements));

  /* Indicate that the buffer is not live. */
  v->nPendingData = -1;

  *ppVTab = &v->base;
  FTSTRACE(("FTS3 Connect %p\n", v));

  return rc;

err:
  fulltext_vtab_destroy(v);
  return rc;
}

static int fulltextConnect(
  sqlite3 *db,
  void *pAux,
  int argc, const char *const*argv,
  sqlite3_vtab **ppVTab,
  char **pzErr
){
  TableSpec spec;
  int rc = parseSpec(&spec, argc, argv, pzErr);
  if( rc!=SQLITE_OK ) return rc;

  rc = constructVtab(db, (fts3Hash *)pAux, &spec, ppVTab, pzErr);
  clearTableSpec(&spec);
  return rc;
}

/* The %_content table holds the text of each document, with
** the docid column exposed as the SQLite rowid for the table.
*/
/* TODO(shess) This comment needs elaboration to match the updated
** code.  Work it into the top-of-file comment at that time.
*/
static int fulltextCreate(sqlite3 *db, void *pAux,
                          int argc, const char * const *argv,
                          sqlite3_vtab **ppVTab, char **pzErr){
  int rc;
  TableSpec spec;
  StringBuffer schema;
  FTSTRACE(("FTS3 Create\n"));

  rc = parseSpec(&spec, argc, argv, pzErr);
  if( rc!=SQLITE_OK ) return rc;

  initStringBuffer(&schema);
  append(&schema, "CREATE TABLE %_content(");
  append(&schema, "  docid INTEGER PRIMARY KEY,");
  appendList(&schema, spec.nColumn, spec.azContentColumn);
  append(&schema, ")");
  rc = sql_exec(db, spec.zDb, spec.zName, stringBufferData(&schema));
  stringBufferDestroy(&schema);
  if( rc!=SQLITE_OK ) goto out;

  rc = sql_exec(db, spec.zDb, spec.zName,
                "create table %_segments("
                "  blockid INTEGER PRIMARY KEY,"
                "  block blob"
                ");"
                );
  if( rc!=SQLITE_OK ) goto out;

  rc = sql_exec(db, spec.zDb, spec.zName,
                "create table %_segdir("
                "  level integer,"
                "  idx integer,"
                "  start_block integer,"
                "  leaves_end_block integer,"
                "  end_block integer,"
                "  root blob,"
                "  primary key(level, idx)"
                ");");
  if( rc!=SQLITE_OK ) goto out;

  rc = constructVtab(db, (fts3Hash *)pAux, &spec, ppVTab, pzErr);

out:
  clearTableSpec(&spec);
  return rc;
}

/* Decide how to handle an SQL query. */
static int fulltextBestIndex(sqlite3_vtab *pVTab, sqlite3_index_info *pInfo){
  fulltext_vtab *v = (fulltext_vtab *)pVTab;
  int i;
  FTSTRACE(("FTS3 BestIndex\n"));

  for(i=0; i<pInfo->nConstraint; ++i){
    const struct sqlite3_index_constraint *pConstraint;
    pConstraint = &pInfo->aConstraint[i];
    if( pConstraint->usable ) {
      if( (pConstraint->iColumn==-1 || pConstraint->iColumn==v->nColumn+1) &&
          pConstraint->op==SQLITE_INDEX_CONSTRAINT_EQ ){
        pInfo->idxNum = QUERY_DOCID;      /* lookup by docid */
        FTSTRACE(("FTS3 QUERY_DOCID\n"));
      } else if( pConstraint->iColumn>=0 && pConstraint->iColumn<=v->nColumn &&
                 pConstraint->op==SQLITE_INDEX_CONSTRAINT_MATCH ){
        /* full-text search */
        pInfo->idxNum = QUERY_FULLTEXT + pConstraint->iColumn;
        FTSTRACE(("FTS3 QUERY_FULLTEXT %d\n", pConstraint->iColumn));
      } else continue;

      pInfo->aConstraintUsage[i].argvIndex = 1;
      pInfo->aConstraintUsage[i].omit = 1;

      /* An arbitrary value for now.
       * TODO: Perhaps docid matches should be considered cheaper than
       * full-text searches. */
      pInfo->estimatedCost = 1.0;   

      return SQLITE_OK;
    }
  }
  pInfo->idxNum = QUERY_GENERIC;
  return SQLITE_OK;
}

static int fulltextDisconnect(sqlite3_vtab *pVTab){
  FTSTRACE(("FTS3 Disconnect %p\n", pVTab));
  fulltext_vtab_destroy((fulltext_vtab *)pVTab);
  return SQLITE_OK;
}

static int fulltextDestroy(sqlite3_vtab *pVTab){
  fulltext_vtab *v = (fulltext_vtab *)pVTab;
  int rc;

  FTSTRACE(("FTS3 Destroy %p\n", pVTab));
  rc = sql_exec(v->db, v->zDb, v->zName,
                "drop table if exists %_content;"
                "drop table if exists %_segments;"
                "drop table if exists %_segdir;"
                );
  if( rc!=SQLITE_OK ) return rc;

  fulltext_vtab_destroy((fulltext_vtab *)pVTab);
  return SQLITE_OK;
}

static int fulltextOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
  fulltext_cursor *c;

  c = (fulltext_cursor *) sqlite3_malloc(sizeof(fulltext_cursor));
  if( c ){
    memset(c, 0, sizeof(fulltext_cursor));
    /* sqlite will initialize c->base */
    *ppCursor = &c->base;
    FTSTRACE(("FTS3 Open %p: %p\n", pVTab, c));
    return SQLITE_OK;
  }else{
    return SQLITE_NOMEM;
  }
}

/* Free all of the dynamically allocated memory held by the
** Snippet
*/
static void snippetClear(Snippet *p){
  sqlite3_free(p->aMatch);
  sqlite3_free(p->zOffset);
  sqlite3_free(p->zSnippet);
  CLEAR(p);
}

/*
** Append a single entry to the p->aMatch[] log.
*/
static void snippetAppendMatch(
  Snippet *p,               /* Append the entry to this snippet */
  int iCol, int iTerm,      /* The column and query term */
  int iToken,               /* Matching token in document */
  int iStart, int nByte     /* Offset and size of the match */
){
  int i;
  struct snippetMatch *pMatch;
  if( p->nMatch+1>=p->nAlloc ){
    p->nAlloc = p->nAlloc*2 + 10;
    p->aMatch = sqlite3_realloc(p->aMatch, p->nAlloc*sizeof(p->aMatch[0]) );
    if( p->aMatch==0 ){
      p->nMatch = 0;
      p->nAlloc = 0;
      return;
    }
  }
  i = p->nMatch++;
  pMatch = &p->aMatch[i];
  pMatch->iCol = iCol;
  pMatch->iTerm = iTerm;
  pMatch->iToken = iToken;
  pMatch->iStart = iStart;
  pMatch->nByte = nByte;
}

/*
** Sizing information for the circular buffer used in snippetOffsetsOfColumn()
*/
#define FTS3_ROTOR_SZ   (32)
#define FTS3_ROTOR_MASK (FTS3_ROTOR_SZ-1)

/*
** Function to iterate through the tokens of a compiled expression.
**
** Except, skip all tokens on the right-hand side of a NOT operator.
** This function is used to find tokens as part of snippet and offset
** generation and we do nt want snippets and offsets to report matches
** for tokens on the RHS of a NOT.
*/
static int fts3NextExprToken(Fts3Expr **ppExpr, int *piToken){
  Fts3Expr *p = *ppExpr;
  int iToken = *piToken;
  if( iToken<0 ){
    /* In this case the expression p is the root of an expression tree.
    ** Move to the first token in the expression tree.
    */
    while( p->pLeft ){
      p = p->pLeft;
    }
    iToken = 0;
  }else{
    assert(p && p->eType==FTSQUERY_PHRASE );
    if( iToken<(p->pPhrase->nToken-1) ){
      iToken++;
    }else{
      iToken = 0;
      while( p->pParent && p->pParent->pLeft!=p ){
        assert( p->pParent->pRight==p );
        p = p->pParent;
      }
      p = p->pParent;
      if( p ){
        assert( p->pRight!=0 );
        p = p->pRight;
        while( p->pLeft ){
          p = p->pLeft;
        }
      }
    }
  }

  *ppExpr = p;
  *piToken = iToken;
  return p?1:0;
}

/*
** Return TRUE if the expression node pExpr is located beneath the
** RHS of a NOT operator.
*/
static int fts3ExprBeneathNot(Fts3Expr *p){
  Fts3Expr *pParent;
  while( p ){
    pParent = p->pParent;
    if( pParent && pParent->eType==FTSQUERY_NOT && pParent->pRight==p ){
      return 1;
    }
    p = pParent;
  }
  return 0;
}

/*
** Add entries to pSnippet->aMatch[] for every match that occurs against
** document zDoc[0..nDoc-1] which is stored in column iColumn.
*/
static void snippetOffsetsOfColumn(
  fulltext_cursor *pCur,         /* The fulltest search cursor */
  Snippet *pSnippet,             /* The Snippet object to be filled in */
  int iColumn,                   /* Index of fulltext table column */
  const char *zDoc,              /* Text of the fulltext table column */
  int nDoc                       /* Length of zDoc in bytes */
){
  const sqlite3_tokenizer_module *pTModule;  /* The tokenizer module */
  sqlite3_tokenizer *pTokenizer;             /* The specific tokenizer */
  sqlite3_tokenizer_cursor *pTCursor;        /* Tokenizer cursor */
  fulltext_vtab *pVtab;                /* The full text index */
  int nColumn;                         /* Number of columns in the index */
  int i, j;                            /* Loop counters */
  int rc;                              /* Return code */
  unsigned int match, prevMatch;       /* Phrase search bitmasks */
  const char *zToken;                  /* Next token from the tokenizer */
  int nToken;                          /* Size of zToken */
  int iBegin, iEnd, iPos;              /* Offsets of beginning and end */

  /* The following variables keep a circular buffer of the last
  ** few tokens */
  unsigned int iRotor = 0;             /* Index of current token */
  int iRotorBegin[FTS3_ROTOR_SZ];      /* Beginning offset of token */
  int iRotorLen[FTS3_ROTOR_SZ];        /* Length of token */

  pVtab = cursor_vtab(pCur);
  nColumn = pVtab->nColumn;
  pTokenizer = pVtab->pTokenizer;
  pTModule = pTokenizer->pModule;
  rc = pTModule->xOpen(pTokenizer, zDoc, nDoc, &pTCursor);
  if( rc ) return;
  pTCursor->pTokenizer = pTokenizer;

  prevMatch = 0;
  while( !pTModule->xNext(pTCursor, &zToken, &nToken, &iBegin, &iEnd, &iPos) ){
    Fts3Expr *pIter = pCur->pExpr;
    int iIter = -1;
    iRotorBegin[iRotor&FTS3_ROTOR_MASK] = iBegin;
    iRotorLen[iRotor&FTS3_ROTOR_MASK] = iEnd-iBegin;
    match = 0;
    for(i=0; i<(FTS3_ROTOR_SZ-1) && fts3NextExprToken(&pIter, &iIter); i++){
      int nPhrase;                    /* Number of tokens in current phrase */
      struct PhraseToken *pToken;     /* Current token */
      int iCol;                       /* Column index */

      if( fts3ExprBeneathNot(pIter) ) continue;
      nPhrase = pIter->pPhrase->nToken;
      pToken = &pIter->pPhrase->aToken[iIter];
      iCol = pIter->pPhrase->iColumn;
      if( iCol>=0 && iCol<nColumn && iCol!=iColumn ) continue;
      if( pToken->n>nToken ) continue;
      if( !pToken->isPrefix && pToken->n<nToken ) continue;
      assert( pToken->n<=nToken );
      if( memcmp(pToken->z, zToken, pToken->n) ) continue;
      if( iIter>0 && (prevMatch & (1<<i))==0 ) continue;
      match |= 1<<i;
      if( i==(FTS3_ROTOR_SZ-2) || nPhrase==iIter+1 ){
        for(j=nPhrase-1; j>=0; j--){
          int k = (iRotor-j) & FTS3_ROTOR_MASK;
          snippetAppendMatch(pSnippet, iColumn, i-j, iPos-j,
                iRotorBegin[k], iRotorLen[k]);
        }
      }
    }
    prevMatch = match<<1;
    iRotor++;
  }
  pTModule->xClose(pTCursor);  
}

/*
** Remove entries from the pSnippet structure to account for the NEAR
** operator. When this is called, pSnippet contains the list of token 
** offsets produced by treating all NEAR operators as AND operators.
** This function removes any entries that should not be present after
** accounting for the NEAR restriction. For example, if the queried
** document is:
**
**     "A B C D E A"
**
** and the query is:
** 
**     A NEAR/0 E
**
** then when this function is called the Snippet contains token offsets
** 0, 4 and 5. This function removes the "0" entry (because the first A
** is not near enough to an E).
**
** When this function is called, the value pointed to by parameter piLeft is
** the integer id of the left-most token in the expression tree headed by
** pExpr. This function increments *piLeft by the total number of tokens
** in the expression tree headed by pExpr.
**
** Return 1 if any trimming occurs.  Return 0 if no trimming is required.
*/
static int trimSnippetOffsets(
  Fts3Expr *pExpr,      /* The search expression */
  Snippet *pSnippet,    /* The set of snippet offsets to be trimmed */
  int *piLeft           /* Index of left-most token in pExpr */
){
  if( pExpr ){
    if( trimSnippetOffsets(pExpr->pLeft, pSnippet, piLeft) ){
      return 1;
    }

    switch( pExpr->eType ){
      case FTSQUERY_PHRASE:
        *piLeft += pExpr->pPhrase->nToken;
        break;
      case FTSQUERY_NEAR: {
        /* The right-hand-side of a NEAR operator is always a phrase. The
        ** left-hand-side is either a phrase or an expression tree that is 
        ** itself headed by a NEAR operator. The following initializations
        ** set local variable iLeft to the token number of the left-most
        ** token in the right-hand phrase, and iRight to the right most
        ** token in the same phrase. For example, if we had:
        **
        **     <col> MATCH '"abc def" NEAR/2 "ghi jkl"'
        **
        ** then iLeft will be set to 2 (token number of ghi) and nToken will
        ** be set to 4.
        */
        Fts3Expr *pLeft = pExpr->pLeft;
        Fts3Expr *pRight = pExpr->pRight;
        int iLeft = *piLeft;
        int nNear = pExpr->nNear;
        int nToken = pRight->pPhrase->nToken;
        int jj, ii;
        if( pLeft->eType==FTSQUERY_NEAR ){
          pLeft = pLeft->pRight;
        }
        assert( pRight->eType==FTSQUERY_PHRASE );
        assert( pLeft->eType==FTSQUERY_PHRASE );
        nToken += pLeft->pPhrase->nToken;

        for(ii=0; ii<pSnippet->nMatch; ii++){
          struct snippetMatch *p = &pSnippet->aMatch[ii];
          if( p->iTerm==iLeft ){
            int isOk = 0;
            /* Snippet ii is an occurence of query term iLeft in the document.
            ** It occurs at position (p->iToken) of the document. We now
            ** search for an instance of token (iLeft-1) somewhere in the 
            ** range (p->iToken - nNear)...(p->iToken + nNear + nToken) within 
            ** the set of snippetMatch structures. If one is found, proceed. 
            ** If one cannot be found, then remove snippets ii..(ii+N-1) 
            ** from the matching snippets, where N is the number of tokens 
            ** in phrase pRight->pPhrase.
            */
            for(jj=0; isOk==0 && jj<pSnippet->nMatch; jj++){
              struct snippetMatch *p2 = &pSnippet->aMatch[jj];
              if( p2->iTerm==(iLeft-1) ){
                if( p2->iToken>=(p->iToken-nNear-1) 
                 && p2->iToken<(p->iToken+nNear+nToken) 
                ){
                  isOk = 1;
                }
              }
            }
            if( !isOk ){
              int kk;
              for(kk=0; kk<pRight->pPhrase->nToken; kk++){
                pSnippet->aMatch[kk+ii].iTerm = -2;
              }
              return 1;
            }
          }
          if( p->iTerm==(iLeft-1) ){
            int isOk = 0;
            for(jj=0; isOk==0 && jj<pSnippet->nMatch; jj++){
              struct snippetMatch *p2 = &pSnippet->aMatch[jj];
              if( p2->iTerm==iLeft ){
                if( p2->iToken<=(p->iToken+nNear+1) 
                 && p2->iToken>(p->iToken-nNear-nToken) 
                ){
                  isOk = 1;
                }
              }
            }
            if( !isOk ){
              int kk;
              for(kk=0; kk<pLeft->pPhrase->nToken; kk++){
                pSnippet->aMatch[ii-kk].iTerm = -2;
              }
              return 1;
            }
          }
        }
        break;
      }
    }

    if( trimSnippetOffsets(pExpr->pRight, pSnippet, piLeft) ){
      return 1;
    }
  }
  return 0;
}

/*
** Compute all offsets for the current row of the query.  
** If the offsets have already been computed, this routine is a no-op.
*/
static void snippetAllOffsets(fulltext_cursor *p){
  int nColumn;
  int iColumn, i;
  int iFirst, iLast;
  int iTerm = 0;
  fulltext_vtab *pFts = cursor_vtab(p);

  if( p->snippet.nMatch || p->pExpr==0 ){
    return;
  }
  nColumn = pFts->nColumn;
  iColumn = (p->iCursorType - QUERY_FULLTEXT);
  if( iColumn<0 || iColumn>=nColumn ){
    /* Look for matches over all columns of the full-text index */
    iFirst = 0;
    iLast = nColumn-1;
  }else{
    /* Look for matches in the iColumn-th column of the index only */
    iFirst = iColumn;
    iLast = iColumn;
  }
  for(i=iFirst; i<=iLast; i++){
    const char *zDoc;
    int nDoc;
    zDoc = (const char*)sqlite3_column_text(p->pStmt, i+1);
    nDoc = sqlite3_column_bytes(p->pStmt, i+1);
    snippetOffsetsOfColumn(p, &p->snippet, i, zDoc, nDoc);
  }

  while( trimSnippetOffsets(p->pExpr, &p->snippet, &iTerm) ){
    iTerm = 0;
  }
}

/*
** Convert the information in the aMatch[] array of the snippet
** into the string zOffset[0..nOffset-1]. This string is used as
** the return of the SQL offsets() function.
*/
static void snippetOffsetText(Snippet *p){
  int i;
  int cnt = 0;
  StringBuffer sb;
  char zBuf[200];
  if( p->zOffset ) return;
  initStringBuffer(&sb);
  for(i=0; i<p->nMatch; i++){
    struct snippetMatch *pMatch = &p->aMatch[i];
    if( pMatch->iTerm>=0 ){
      /* If snippetMatch.iTerm is less than 0, then the match was 
      ** discarded as part of processing the NEAR operator (see the 
      ** trimSnippetOffsetsForNear() function for details). Ignore 
      ** it in this case
      */
      zBuf[0] = ' ';
      sqlite3_snprintf(sizeof(zBuf)-1, &zBuf[cnt>0], "%d %d %d %d",
          pMatch->iCol, pMatch->iTerm, pMatch->iStart, pMatch->nByte);
      append(&sb, zBuf);
      cnt++;
    }
  }
  p->zOffset = stringBufferData(&sb);
  p->nOffset = stringBufferLength(&sb);
}

/*
** zDoc[0..nDoc-1] is phrase of text.  aMatch[0..nMatch-1] are a set
** of matching words some of which might be in zDoc.  zDoc is column
** number iCol.
**
** iBreak is suggested spot in zDoc where we could begin or end an
** excerpt.  Return a value similar to iBreak but possibly adjusted
** to be a little left or right so that the break point is better.
*/
static int wordBoundary(
  int iBreak,                   /* The suggested break point */
  const char *zDoc,             /* Document text */
  int nDoc,                     /* Number of bytes in zDoc[] */
  struct snippetMatch *aMatch,  /* Matching words */
  int nMatch,                   /* Number of entries in aMatch[] */
  int iCol                      /* The column number for zDoc[] */
){
  int i;
  if( iBreak<=10 ){
    return 0;
  }
  if( iBreak>=nDoc-10 ){
    return nDoc;
  }
  for(i=0; i<nMatch && aMatch[i].iCol<iCol; i++){}
  while( i<nMatch && aMatch[i].iStart+aMatch[i].nByte<iBreak ){ i++; }
  if( i<nMatch ){
    if( aMatch[i].iStart<iBreak+10 ){
      return aMatch[i].iStart;
    }
    if( i>0 && aMatch[i-1].iStart+aMatch[i-1].nByte>=iBreak ){
      return aMatch[i-1].iStart;
    }
  }
  for(i=1; i<=10; i++){
    if( safe_isspace(zDoc[iBreak-i]) ){
      return iBreak - i + 1;
    }
    if( safe_isspace(zDoc[iBreak+i]) ){
      return iBreak + i + 1;
    }
  }
  return iBreak;
}



/*
** Allowed values for Snippet.aMatch[].snStatus
*/
#define SNIPPET_IGNORE  0   /* It is ok to omit this match from the snippet */
#define SNIPPET_DESIRED 1   /* We want to include this match in the snippet */

/*
** Generate the text of a snippet.
*/
static void snippetText(
  fulltext_cursor *pCursor,   /* The cursor we need the snippet for */
  const char *zStartMark,     /* Markup to appear before each match */
  const char *zEndMark,       /* Markup to appear after each match */
  const char *zEllipsis       /* Ellipsis mark */
){
  int i, j;
  struct snippetMatch *aMatch;
  int nMatch;
  int nDesired;
  StringBuffer sb;
  int tailCol;
  int tailOffset;
  int iCol;
  int nDoc;
  const char *zDoc;
  int iStart, iEnd;
  int tailEllipsis = 0;
  int iMatch;
  

  sqlite3_free(pCursor->snippet.zSnippet);
  pCursor->snippet.zSnippet = 0;
  aMatch = pCursor->snippet.aMatch;
  nMatch = pCursor->snippet.nMatch;
  initStringBuffer(&sb);

  for(i=0; i<nMatch; i++){
    aMatch[i].snStatus = SNIPPET_IGNORE;
  }
  nDesired = 0;
  for(i=0; i<FTS3_ROTOR_SZ; i++){
    for(j=0; j<nMatch; j++){
      if( aMatch[j].iTerm==i ){
        aMatch[j].snStatus = SNIPPET_DESIRED;
        nDesired++;
        break;
      }
    }
  }

  iMatch = 0;
  tailCol = -1;
  tailOffset = 0;
  for(i=0; i<nMatch && nDesired>0; i++){
    if( aMatch[i].snStatus!=SNIPPET_DESIRED ) continue;
    nDesired--;
    iCol = aMatch[i].iCol;
    zDoc = (const char*)sqlite3_column_text(pCursor->pStmt, iCol+1);
    nDoc = sqlite3_column_bytes(pCursor->pStmt, iCol+1);
    iStart = aMatch[i].iStart - 40;
    iStart = wordBoundary(iStart, zDoc, nDoc, aMatch, nMatch, iCol);
    if( iStart<=10 ){
      iStart = 0;
    }
    if( iCol==tailCol && iStart<=tailOffset+20 ){
      iStart = tailOffset;
    }
    if( (iCol!=tailCol && tailCol>=0) || iStart!=tailOffset ){
      trimWhiteSpace(&sb);
      appendWhiteSpace(&sb);
      append(&sb, zEllipsis);
      appendWhiteSpace(&sb);
    }
    iEnd = aMatch[i].iStart + aMatch[i].nByte + 40;
    iEnd = wordBoundary(iEnd, zDoc, nDoc, aMatch, nMatch, iCol);
    if( iEnd>=nDoc-10 ){
      iEnd = nDoc;
      tailEllipsis = 0;
    }else{
      tailEllipsis = 1;
    }
    while( iMatch<nMatch && aMatch[iMatch].iCol<iCol ){ iMatch++; }
    while( iStart<iEnd ){
      while( iMatch<nMatch && aMatch[iMatch].iStart<iStart
             && aMatch[iMatch].iCol<=iCol ){
        iMatch++;
      }
      if( iMatch<nMatch && aMatch[iMatch].iStart<iEnd
             && aMatch[iMatch].iCol==iCol ){
        nappend(&sb, &zDoc[iStart], aMatch[iMatch].iStart - iStart);
        iStart = aMatch[iMatch].iStart;
        append(&sb, zStartMark);
        nappend(&sb, &zDoc[iStart], aMatch[iMatch].nByte);
        append(&sb, zEndMark);
        iStart += aMatch[iMatch].nByte;
        for(j=iMatch+1; j<nMatch; j++){
          if( aMatch[j].iTerm==aMatch[iMatch].iTerm
              && aMatch[j].snStatus==SNIPPET_DESIRED ){
            nDesired--;
            aMatch[j].snStatus = SNIPPET_IGNORE;
          }
        }
      }else{
        nappend(&sb, &zDoc[iStart], iEnd - iStart);
        iStart = iEnd;
      }
    }
    tailCol = iCol;
    tailOffset = iEnd;
  }
  trimWhiteSpace(&sb);
  if( tailEllipsis ){
    appendWhiteSpace(&sb);
    append(&sb, zEllipsis);
  }
  pCursor->snippet.zSnippet = stringBufferData(&sb);
  pCursor->snippet.nSnippet = stringBufferLength(&sb);
}


/*
** Close the cursor.  For additional information see the documentation
** on the xClose method of the virtual table interface.
*/
static int fulltextClose(sqlite3_vtab_cursor *pCursor){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  FTSTRACE(("FTS3 Close %p\n", c));
  sqlite3_finalize(c->pStmt);
  sqlite3Fts3ExprFree(c->pExpr);
  snippetClear(&c->snippet);
  if( c->result.nData!=0 ){
    dlrDestroy(&c->reader);
  }
  dataBufferDestroy(&c->result);
  sqlite3_free(c);
  return SQLITE_OK;
}

static int fulltextNext(sqlite3_vtab_cursor *pCursor){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  int rc;

  FTSTRACE(("FTS3 Next %p\n", pCursor));
  snippetClear(&c->snippet);
  if( c->iCursorType < QUERY_FULLTEXT ){
    /* TODO(shess) Handle SQLITE_SCHEMA AND SQLITE_BUSY. */
    rc = sqlite3_step(c->pStmt);
    switch( rc ){
      case SQLITE_ROW:
        c->eof = 0;
        return SQLITE_OK;
      case SQLITE_DONE:
        c->eof = 1;
        return SQLITE_OK;
      default:
        c->eof = 1;
        return rc;
    }
  } else {  /* full-text query */
    rc = sqlite3_reset(c->pStmt);
    if( rc!=SQLITE_OK ) return rc;

    if( c->result.nData==0 || dlrAtEnd(&c->reader) ){
      c->eof = 1;
      return SQLITE_OK;
    }
    rc = sqlite3_bind_int64(c->pStmt, 1, dlrDocid(&c->reader));
    dlrStep(&c->reader);
    if( rc!=SQLITE_OK ) return rc;
    /* TODO(shess) Handle SQLITE_SCHEMA AND SQLITE_BUSY. */
    rc = sqlite3_step(c->pStmt);
    if( rc==SQLITE_ROW ){   /* the case we expect */
      c->eof = 0;
      return SQLITE_OK;
    }
    /* an error occurred; abort */
    return rc==SQLITE_DONE ? SQLITE_ERROR : rc;
  }
}


/* TODO(shess) If we pushed LeafReader to the top of the file, or to
** another file, term_select() could be pushed above
** docListOfTerm().
*/
static int termSelect(fulltext_vtab *v, int iColumn,
                      const char *pTerm, int nTerm, int isPrefix,
                      DocListType iType, DataBuffer *out);

/* 
** Return a DocList corresponding to the phrase *pPhrase.
**
** The resulting DL_DOCIDS doclist is stored in pResult, which is
** overwritten.
*/
static int docListOfPhrase(
  fulltext_vtab *pTab,   /* The full text index */
  Fts3Phrase *pPhrase,   /* Phrase to return a doclist corresponding to */
  DocListType eListType, /* Either DL_DOCIDS or DL_POSITIONS */
  DataBuffer *pResult    /* Write the result here */
){
  int ii;
  int rc = SQLITE_OK;
  int iCol = pPhrase->iColumn;
  DocListType eType = eListType;
  assert( eType==DL_POSITIONS || eType==DL_DOCIDS );
  if( pPhrase->nToken>1 ){
    eType = DL_POSITIONS;
  }

  /* This code should never be called with buffered updates. */
  assert( pTab->nPendingData<0 );

  for(ii=0; rc==SQLITE_OK && ii<pPhrase->nToken; ii++){
    DataBuffer tmp;
    struct PhraseToken *p = &pPhrase->aToken[ii];
    rc = termSelect(pTab, iCol, p->z, p->n, p->isPrefix, eType, &tmp);
    if( rc==SQLITE_OK ){
      if( ii==0 ){
        *pResult = tmp;
      }else{
        DataBuffer res = *pResult;
        dataBufferInit(pResult, 0);
        if( ii==(pPhrase->nToken-1) ){
          eType = eListType;
        }
        docListPhraseMerge(
          res.pData, res.nData, tmp.pData, tmp.nData, 0, 0, eType, pResult
        );
        dataBufferDestroy(&res);
        dataBufferDestroy(&tmp);
      }























































































































































































    }
  }







  return rc;
}

/*
** Evaluate the full-text expression pExpr against fts3 table pTab. Write
** the results into pRes.
*/
static int evalFts3Expr(
  fulltext_vtab *pTab,           /* Fts3 Virtual table object */
  Fts3Expr *pExpr,               /* Parsed fts3 expression */
  DataBuffer *pRes               /* OUT: Write results of the expression here */

){
  int rc = SQLITE_OK;

  /* Initialize the output buffer. If this is an empty query (pExpr==0), 
  ** this is all that needs to be done. Empty queries produce empty 
  ** result sets.
  */
  dataBufferInit(pRes, 0);

  if( pExpr ){
    if( pExpr->eType==FTSQUERY_PHRASE ){
      DocListType eType = DL_DOCIDS;
      if( pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR ){
        eType = DL_POSITIONS;
      }
      rc = docListOfPhrase(pTab, pExpr->pPhrase, eType, pRes);

    }else{



      DataBuffer lhs;
      DataBuffer rhs;

      dataBufferInit(&rhs, 0);
      if( SQLITE_OK==(rc = evalFts3Expr(pTab, pExpr->pLeft, &lhs)) 
       && SQLITE_OK==(rc = evalFts3Expr(pTab, pExpr->pRight, &rhs)) 
      ){



        switch( pExpr->eType ){
          case FTSQUERY_NEAR: {
            int nToken;
            Fts3Expr *pLeft;
            DocListType eType = DL_DOCIDS;





            if( pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR ){
              eType = DL_POSITIONS;

            }
            pLeft = pExpr->pLeft;
            while( pLeft->eType==FTSQUERY_NEAR ){ 
              pLeft=pLeft->pRight;
            }

            assert( pExpr->pRight->eType==FTSQUERY_PHRASE );
            assert( pLeft->eType==FTSQUERY_PHRASE );
            nToken = pLeft->pPhrase->nToken + pExpr->pRight->pPhrase->nToken;
            docListPhraseMerge(lhs.pData, lhs.nData, rhs.pData, rhs.nData, 

                pExpr->nNear+1, nToken, eType, pRes




            );
            break;




          }
          case FTSQUERY_NOT: {
            docListExceptMerge(lhs.pData, lhs.nData, rhs.pData, rhs.nData,pRes);

            break;
          }

          case FTSQUERY_AND: {
            docListAndMerge(lhs.pData, lhs.nData, rhs.pData, rhs.nData, pRes);











            break;
          }
          case FTSQUERY_OR: {
            docListOrMerge(lhs.pData, lhs.nData, rhs.pData, rhs.nData, pRes);







            break;
          }
        }
      }
      dataBufferDestroy(&lhs);
      dataBufferDestroy(&rhs);
    }
  }

  return rc;
}

/* TODO(shess) Refactor the code to remove this forward decl. */
static int flushPendingTerms(fulltext_vtab *v);

/* Perform a full-text query using the search expression in
** zInput[0..nInput-1].  Return a list of matching documents
** in pResult.
**
** Queries must match column iColumn.  Or if iColumn>=nColumn
** they are allowed to match against any column.
*/
static int fulltextQuery(
  fulltext_vtab *v,      /* The full text index */
  int iColumn,           /* Match against this column by default */
  const char *zInput,    /* The query string */
  int nInput,            /* Number of bytes in zInput[] */
  DataBuffer *pResult,   /* Write the result doclist here */
  Fts3Expr **ppExpr        /* Put parsed query string here */
){
  int rc;

  /* TODO(shess) Instead of flushing pendingTerms, we could query for
  ** the relevant term and merge the doclist into what we receive from
  ** the database.  Wait and see if this is a common issue, first.
  **
  ** A good reason not to flush is to not generate update-related
  ** error codes from here.
  */

  /* Flush any buffered updates before executing the query. */
  rc = flushPendingTerms(v);
  if( rc!=SQLITE_OK ){
    return rc;
  }

  /* Parse the query passed to the MATCH operator. */
  rc = sqlite3Fts3ExprParse(v->pTokenizer, 
      v->azColumn, v->nColumn, iColumn, zInput, nInput, ppExpr
  );
  if( rc!=SQLITE_OK ){
    assert( 0==(*ppExpr) );
    return rc;
  }

  return evalFts3Expr(v, *ppExpr, pResult);
}

/*
** This is the xFilter interface for the virtual table.  See
** the virtual table xFilter method documentation for additional
** information.
**
** If idxNum==QUERY_GENERIC then do a full table scan against
** the %_content table.
**
** If idxNum==QUERY_DOCID then do a docid lookup for a single entry
** in the %_content table.
**
** If idxNum>=QUERY_FULLTEXT then use the full text index.  The
** column on the left-hand side of the MATCH operator is column
** number idxNum-QUERY_FULLTEXT, 0 indexed.  argv[0] is the right-hand
** side of the MATCH operator.
*/
/* TODO(shess) Upgrade the cursor initialization and destruction to
** account for fulltextFilter() being called multiple times on the
** same cursor.  The current solution is very fragile.  Apply fix to
** fts3 as appropriate.
*/
static int fulltextFilter(
  sqlite3_vtab_cursor *pCursor,     /* The cursor used for this query */
  int idxNum, const char *idxStr,   /* Which indexing scheme to use */
  int argc, sqlite3_value **argv    /* Arguments for the indexing scheme */
){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  fulltext_vtab *v = cursor_vtab(c);
  int rc;

  FTSTRACE(("FTS3 Filter %p\n",pCursor));

  /* If the cursor has a statement that was not prepared according to
  ** idxNum, clear it.  I believe all calls to fulltextFilter with a
  ** given cursor will have the same idxNum , but in this case it's
  ** easy to be safe.
  */
  if( c->pStmt && c->iCursorType!=idxNum ){
    sqlite3_finalize(c->pStmt);
    c->pStmt = NULL;
  }

  /* Get a fresh statement appropriate to idxNum. */
  /* TODO(shess): Add a prepared-statement cache in the vt structure.
  ** The cache must handle multiple open cursors.  Easier to cache the
  ** statement variants at the vt to reduce malloc/realloc/free here.
  ** Or we could have a StringBuffer variant which allowed stack
  ** construction for small values.
  */
  if( !c->pStmt ){
    StringBuffer sb;
    initStringBuffer(&sb);
    append(&sb, "SELECT docid, ");
    appendList(&sb, v->nColumn, v->azContentColumn);
    append(&sb, " FROM %_content");
    if( idxNum!=QUERY_GENERIC ) append(&sb, " WHERE docid = ?");
    rc = sql_prepare(v->db, v->zDb, v->zName, &c->pStmt,
                     stringBufferData(&sb));
    stringBufferDestroy(&sb);
    if( rc!=SQLITE_OK ) return rc;
    c->iCursorType = idxNum;
  }else{
    sqlite3_reset(c->pStmt);
    assert( c->iCursorType==idxNum );
  }

  switch( idxNum ){
    case QUERY_GENERIC:
      break;

    case QUERY_DOCID:
      rc = sqlite3_bind_int64(c->pStmt, 1, sqlite3_value_int64(argv[0]));
      if( rc!=SQLITE_OK ) return rc;
      break;

    default:   /* full-text search */
    {
      int iCol = idxNum-QUERY_FULLTEXT;
      const char *zQuery = (const char *)sqlite3_value_text(argv[0]);
      assert( idxNum<=QUERY_FULLTEXT+v->nColumn);
      assert( argc==1 );
      if( c->result.nData!=0 ){
        /* This case happens if the same cursor is used repeatedly. */
        dlrDestroy(&c->reader);
        dataBufferReset(&c->result);
      }else{
        dataBufferInit(&c->result, 0);
      }
      rc = fulltextQuery(v, iCol, zQuery, -1, &c->result, &c->pExpr);
      if( rc!=SQLITE_OK ) return rc;
      if( c->result.nData!=0 ){
        dlrInit(&c->reader, DL_DOCIDS, c->result.pData, c->result.nData);
      }
      break;
    }
  }

  return fulltextNext(pCursor);
}

/* This is the xEof method of the virtual table.  The SQLite core
** calls this routine to find out if it has reached the end of
** a query's results set.
*/
static int fulltextEof(sqlite3_vtab_cursor *pCursor){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  return c->eof;
}

/* This is the xColumn method of the virtual table.  The SQLite
** core calls this method during a query when it needs the value
** of a column from the virtual table.  This method needs to use
** one of the sqlite3_result_*() routines to store the requested
** value back in the pContext.
*/
static int fulltextColumn(sqlite3_vtab_cursor *pCursor,
                          sqlite3_context *pContext, int idxCol){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  fulltext_vtab *v = cursor_vtab(c);

  if( idxCol<v->nColumn ){
    sqlite3_value *pVal = sqlite3_column_value(c->pStmt, idxCol+1);
    sqlite3_result_value(pContext, pVal);
  }else if( idxCol==v->nColumn ){
    /* The extra column whose name is the same as the table.
    ** Return a blob which is a pointer to the cursor
    */
    sqlite3_result_blob(pContext, &c, sizeof(c), SQLITE_TRANSIENT);
  }else if( idxCol==v->nColumn+1 ){
    /* The docid column, which is an alias for rowid. */
    sqlite3_value *pVal = sqlite3_column_value(c->pStmt, 0);
    sqlite3_result_value(pContext, pVal);
  }
  return SQLITE_OK;
}

/* This is the xRowid method.  The SQLite core calls this routine to
** retrieve the rowid for the current row of the result set.  fts3
** exposes %_content.docid as the rowid for the virtual table.  The
** rowid should be written to *pRowid.
*/
static int fulltextRowid(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;

  *pRowid = sqlite3_column_int64(c->pStmt, 0);
  return SQLITE_OK;
}

/* Add all terms in [zText] to pendingTerms table.  If [iColumn] > 0,
** we also store positions and offsets in the hash table using that
** column number.
*/
static int buildTerms(fulltext_vtab *v, sqlite_int64 iDocid,
                      const char *zText, int iColumn){
  sqlite3_tokenizer *pTokenizer = v->pTokenizer;
  sqlite3_tokenizer_cursor *pCursor;
  const char *pToken;
  int nTokenBytes;
  int iStartOffset, iEndOffset, iPosition;
  int rc;

  rc = pTokenizer->pModule->xOpen(pTokenizer, zText, -1, &pCursor);
  if( rc!=SQLITE_OK ) return rc;

  pCursor->pTokenizer = pTokenizer;
  while( SQLITE_OK==(rc=pTokenizer->pModule->xNext(pCursor,
                                                   &pToken, &nTokenBytes,
                                                   &iStartOffset, &iEndOffset,
                                                   &iPosition)) ){
    DLCollector *p;
    int nData;                   /* Size of doclist before our update. */

    /* Positions can't be negative; we use -1 as a terminator
     * internally.  Token can't be NULL or empty. */
    if( iPosition<0 || pToken == NULL || nTokenBytes == 0 ){
      rc = SQLITE_ERROR;
      break;
    }

    p = fts3HashFind(&v->pendingTerms, pToken, nTokenBytes);
    if( p==NULL ){
      nData = 0;
      p = dlcNew(iDocid, DL_DEFAULT);
      fts3HashInsert(&v->pendingTerms, pToken, nTokenBytes, p);

      /* Overhead for our hash table entry, the key, and the value. */
      v->nPendingData += sizeof(struct fts3HashElem)+sizeof(*p)+nTokenBytes;
    }else{
      nData = p->b.nData;
      if( p->dlw.iPrevDocid!=iDocid ) dlcNext(p, iDocid);
    }
    if( iColumn>=0 ){
      dlcAddPos(p, iColumn, iPosition, iStartOffset, iEndOffset);
    }

    /* Accumulate data added by dlcNew or dlcNext, and dlcAddPos. */
    v->nPendingData += p->b.nData-nData;
  }

  /* TODO(shess) Check return?  Should this be able to cause errors at
  ** this point?  Actually, same question about sqlite3_finalize(),
  ** though one could argue that failure there means that the data is
  ** not durable.  *ponder*
  */
  pTokenizer->pModule->xClose(pCursor);
  if( SQLITE_DONE == rc ) return SQLITE_OK;
  return rc;
}

/* Add doclists for all terms in [pValues] to pendingTerms table. */
static int insertTerms(fulltext_vtab *v, sqlite_int64 iDocid,
                       sqlite3_value **pValues){
  int i;
  for(i = 0; i < v->nColumn ; ++i){
    char *zText = (char*)sqlite3_value_text(pValues[i]);
    int rc = buildTerms(v, iDocid, zText, i);
    if( rc!=SQLITE_OK ) return rc;
  }
  return SQLITE_OK;
}

/* Add empty doclists for all terms in the given row's content to
** pendingTerms.
*/
static int deleteTerms(fulltext_vtab *v, sqlite_int64 iDocid){
  const char **pValues;
  int i, rc;

  /* TODO(shess) Should we allow such tables at all? */
  if( DL_DEFAULT==DL_DOCIDS ) return SQLITE_ERROR;

  rc = content_select(v, iDocid, &pValues);
  if( rc!=SQLITE_OK ) return rc;

  for(i = 0 ; i < v->nColumn; ++i) {
    rc = buildTerms(v, iDocid, pValues[i], -1);
    if( rc!=SQLITE_OK ) break;
  }

  freeStringArray(v->nColumn, pValues);
  return SQLITE_OK;
}

/* TODO(shess) Refactor the code to remove this forward decl. */
static int initPendingTerms(fulltext_vtab *v, sqlite_int64 iDocid);

/* Insert a row into the %_content table; set *piDocid to be the ID of the
** new row.  Add doclists for terms to pendingTerms.
*/
static int index_insert(fulltext_vtab *v, sqlite3_value *pRequestDocid,
                        sqlite3_value **pValues, sqlite_int64 *piDocid){
  int rc;

  rc = content_insert(v, pRequestDocid, pValues);  /* execute an SQL INSERT */
  if( rc!=SQLITE_OK ) return rc;

  /* docid column is an alias for rowid. */
  *piDocid = sqlite3_last_insert_rowid(v->db);
  rc = initPendingTerms(v, *piDocid);
  if( rc!=SQLITE_OK ) return rc;

  return insertTerms(v, *piDocid, pValues);
}

/* Delete a row from the %_content table; add empty doclists for terms
** to pendingTerms.
*/
static int index_delete(fulltext_vtab *v, sqlite_int64 iRow){
  int rc = initPendingTerms(v, iRow);
  if( rc!=SQLITE_OK ) return rc;

  rc = deleteTerms(v, iRow);
  if( rc!=SQLITE_OK ) return rc;

  return content_delete(v, iRow);  /* execute an SQL DELETE */
}

/* Update a row in the %_content table; add delete doclists to
** pendingTerms for old terms not in the new data, add insert doclists
** to pendingTerms for terms in the new data.
*/
static int index_update(fulltext_vtab *v, sqlite_int64 iRow,
                        sqlite3_value **pValues){
  int rc = initPendingTerms(v, iRow);
  if( rc!=SQLITE_OK ) return rc;

  /* Generate an empty doclist for each term that previously appeared in this
   * row. */
  rc = deleteTerms(v, iRow);
  if( rc!=SQLITE_OK ) return rc;

  rc = content_update(v, pValues, iRow);  /* execute an SQL UPDATE */
  if( rc!=SQLITE_OK ) return rc;

  /* Now add positions for terms which appear in the updated row. */
  return insertTerms(v, iRow, pValues);
}

/*******************************************************************/
/* InteriorWriter is used to collect terms and block references into
** interior nodes in %_segments.  See commentary at top of file for
** format.
*/

/* How large interior nodes can grow. */
#define INTERIOR_MAX 2048

/* Minimum number of terms per interior node (except the root). This
** prevents large terms from making the tree too skinny - must be >0
** so that the tree always makes progress.  Note that the min tree
** fanout will be INTERIOR_MIN_TERMS+1.
*/
#define INTERIOR_MIN_TERMS 7
#if INTERIOR_MIN_TERMS<1
# error INTERIOR_MIN_TERMS must be greater than 0.
#endif

/* ROOT_MAX controls how much data is stored inline in the segment
** directory.
*/
/* TODO(shess) Push ROOT_MAX down to whoever is writing things.  It's
** only here so that interiorWriterRootInfo() and leafWriterRootInfo()
** can both see it, but if the caller passed it in, we wouldn't even
** need a define.
*/
#define ROOT_MAX 1024
#if ROOT_MAX<VARINT_MAX*2
# error ROOT_MAX must have enough space for a header.
#endif

/* InteriorBlock stores a linked-list of interior blocks while a lower
** layer is being constructed.
*/
typedef struct InteriorBlock {
  DataBuffer term;           /* Leftmost term in block's subtree. */
  DataBuffer data;           /* Accumulated data for the block. */
  struct InteriorBlock *next;
} InteriorBlock;

static InteriorBlock *interiorBlockNew(int iHeight, sqlite_int64 iChildBlock,
                                       const char *pTerm, int nTerm){
  InteriorBlock *block = sqlite3_malloc(sizeof(InteriorBlock));
  char c[VARINT_MAX+VARINT_MAX];
  int n;

  if( block ){
    memset(block, 0, sizeof(*block));
    dataBufferInit(&block->term, 0);
    dataBufferReplace(&block->term, pTerm, nTerm);

    n = fts3PutVarint(c, iHeight);
    n += fts3PutVarint(c+n, iChildBlock);
    dataBufferInit(&block->data, INTERIOR_MAX);
    dataBufferReplace(&block->data, c, n);
  }
  return block;
}

#ifndef NDEBUG
/* Verify that the data is readable as an interior node. */
static void interiorBlockValidate(InteriorBlock *pBlock){
  const char *pData = pBlock->data.pData;
  int nData = pBlock->data.nData;
  int n, iDummy;
  sqlite_int64 iBlockid;

  assert( nData>0 );
  assert( pData!=0 );
  assert( pData+nData>pData );

  /* Must lead with height of node as a varint(n), n>0 */
  n = fts3GetVarint32(pData, &iDummy);
  assert( n>0 );
  assert( iDummy>0 );
  assert( n<nData );
  pData += n;
  nData -= n;

  /* Must contain iBlockid. */
  n = fts3GetVarint(pData, &iBlockid);
  assert( n>0 );
  assert( n<=nData );
  pData += n;
  nData -= n;

  /* Zero or more terms of positive length */
  if( nData!=0 ){
    /* First term is not delta-encoded. */
    n = fts3GetVarint32(pData, &iDummy);
    assert( n>0 );
    assert( iDummy>0 );
    assert( n+iDummy>0);
    assert( n+iDummy<=nData );
    pData += n+iDummy;
    nData -= n+iDummy;

    /* Following terms delta-encoded. */
    while( nData!=0 ){
      /* Length of shared prefix. */
      n = fts3GetVarint32(pData, &iDummy);
      assert( n>0 );
      assert( iDummy>=0 );
      assert( n<nData );
      pData += n;
      nData -= n;

      /* Length and data of distinct suffix. */
      n = fts3GetVarint32(pData, &iDummy);
      assert( n>0 );
      assert( iDummy>0 );
      assert( n+iDummy>0);
      assert( n+iDummy<=nData );
      pData += n+iDummy;
      nData -= n+iDummy;
    }
  }
}
#define ASSERT_VALID_INTERIOR_BLOCK(x) interiorBlockValidate(x)
#else
#define ASSERT_VALID_INTERIOR_BLOCK(x) assert( 1 )
#endif

typedef struct InteriorWriter {
  int iHeight;                   /* from 0 at leaves. */
  InteriorBlock *first, *last;
  struct InteriorWriter *parentWriter;

  DataBuffer term;               /* Last term written to block "last". */
  sqlite_int64 iOpeningChildBlock; /* First child block in block "last". */
#ifndef NDEBUG
  sqlite_int64 iLastChildBlock;  /* for consistency checks. */
#endif
} InteriorWriter;

/* Initialize an interior node where pTerm[nTerm] marks the leftmost
** term in the tree.  iChildBlock is the leftmost child block at the
** next level down the tree.
*/
static void interiorWriterInit(int iHeight, const char *pTerm, int nTerm,
                               sqlite_int64 iChildBlock,
                               InteriorWriter *pWriter){
  InteriorBlock *block;
  assert( iHeight>0 );
  CLEAR(pWriter);

  pWriter->iHeight = iHeight;
  pWriter->iOpeningChildBlock = iChildBlock;
#ifndef NDEBUG
  pWriter->iLastChildBlock = iChildBlock;
#endif
  block = interiorBlockNew(iHeight, iChildBlock, pTerm, nTerm);
  pWriter->last = pWriter->first = block;
  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);
  dataBufferInit(&pWriter->term, 0);
}

/* Append the child node rooted at iChildBlock to the interior node,
** with pTerm[nTerm] as the leftmost term in iChildBlock's subtree.
*/
static void interiorWriterAppend(InteriorWriter *pWriter,
                                 const char *pTerm, int nTerm,
                                 sqlite_int64 iChildBlock){
  char c[VARINT_MAX+VARINT_MAX];
  int n, nPrefix = 0;

  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);

  /* The first term written into an interior node is actually
  ** associated with the second child added (the first child was added
  ** in interiorWriterInit, or in the if clause at the bottom of this
  ** function).  That term gets encoded straight up, with nPrefix left
  ** at 0.
  */
  if( pWriter->term.nData==0 ){
    n = fts3PutVarint(c, nTerm);
  }else{
    while( nPrefix<pWriter->term.nData &&
           pTerm[nPrefix]==pWriter->term.pData[nPrefix] ){
      nPrefix++;
    }

    n = fts3PutVarint(c, nPrefix);
    n += fts3PutVarint(c+n, nTerm-nPrefix);
  }

#ifndef NDEBUG
  pWriter->iLastChildBlock++;
#endif
  assert( pWriter->iLastChildBlock==iChildBlock );

  /* Overflow to a new block if the new term makes the current block
  ** too big, and the current block already has enough terms.
  */
  if( pWriter->last->data.nData+n+nTerm-nPrefix>INTERIOR_MAX &&
      iChildBlock-pWriter->iOpeningChildBlock>INTERIOR_MIN_TERMS ){
    pWriter->last->next = interiorBlockNew(pWriter->iHeight, iChildBlock,
                                           pTerm, nTerm);
    pWriter->last = pWriter->last->next;
    pWriter->iOpeningChildBlock = iChildBlock;
    dataBufferReset(&pWriter->term);
  }else{
    dataBufferAppend2(&pWriter->last->data, c, n,
                      pTerm+nPrefix, nTerm-nPrefix);
    dataBufferReplace(&pWriter->term, pTerm, nTerm);
  }
  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);
}

/* Free the space used by pWriter, including the linked-list of
** InteriorBlocks, and parentWriter, if present.
*/
static int interiorWriterDestroy(InteriorWriter *pWriter){
  InteriorBlock *block = pWriter->first;

  while( block!=NULL ){
    InteriorBlock *b = block;
    block = block->next;
    dataBufferDestroy(&b->term);
    dataBufferDestroy(&b->data);
    sqlite3_free(b);
  }
  if( pWriter->parentWriter!=NULL ){
    interiorWriterDestroy(pWriter->parentWriter);
    sqlite3_free(pWriter->parentWriter);
  }
  dataBufferDestroy(&pWriter->term);
  SCRAMBLE(pWriter);
  return SQLITE_OK;
}

/* If pWriter can fit entirely in ROOT_MAX, return it as the root info
** directly, leaving *piEndBlockid unchanged.  Otherwise, flush
** pWriter to %_segments, building a new layer of interior nodes, and
** recursively ask for their root into.
*/
static int interiorWriterRootInfo(fulltext_vtab *v, InteriorWriter *pWriter,
                                  char **ppRootInfo, int *pnRootInfo,
                                  sqlite_int64 *piEndBlockid){
  InteriorBlock *block = pWriter->first;
  sqlite_int64 iBlockid = 0;
  int rc;

  /* If we can fit the segment inline */
  if( block==pWriter->last && block->data.nData<ROOT_MAX ){
    *ppRootInfo = block->data.pData;
    *pnRootInfo = block->data.nData;
    return SQLITE_OK;
  }

  /* Flush the first block to %_segments, and create a new level of
  ** interior node.
  */
  ASSERT_VALID_INTERIOR_BLOCK(block);
  rc = block_insert(v, block->data.pData, block->data.nData, &iBlockid);
  if( rc!=SQLITE_OK ) return rc;
  *piEndBlockid = iBlockid;

  pWriter->parentWriter = sqlite3_malloc(sizeof(*pWriter->parentWriter));
  interiorWriterInit(pWriter->iHeight+1,
                     block->term.pData, block->term.nData,
                     iBlockid, pWriter->parentWriter);

  /* Flush additional blocks and append to the higher interior
  ** node.
  */
  for(block=block->next; block!=NULL; block=block->next){
    ASSERT_VALID_INTERIOR_BLOCK(block);
    rc = block_insert(v, block->data.pData, block->data.nData, &iBlockid);
    if( rc!=SQLITE_OK ) return rc;
    *piEndBlockid = iBlockid;

    interiorWriterAppend(pWriter->parentWriter,
                         block->term.pData, block->term.nData, iBlockid);
  }

  /* Parent node gets the chance to be the root. */
  return interiorWriterRootInfo(v, pWriter->parentWriter,
                                ppRootInfo, pnRootInfo, piEndBlockid);
}

/****************************************************************/
/* InteriorReader is used to read off the data from an interior node
** (see comment at top of file for the format).
*/
typedef struct InteriorReader {
  const char *pData;
  int nData;

  DataBuffer term;          /* previous term, for decoding term delta. */

  sqlite_int64 iBlockid;
} InteriorReader;

static void interiorReaderDestroy(InteriorReader *pReader){
  dataBufferDestroy(&pReader->term);
  SCRAMBLE(pReader);
}

/* TODO(shess) The assertions are great, but what if we're in NDEBUG
** and the blob is empty or otherwise contains suspect data?
*/
static void interiorReaderInit(const char *pData, int nData,
                               InteriorReader *pReader){
  int n, nTerm;

  /* Require at least the leading flag byte */
  assert( nData>0 );
  assert( pData[0]!='\0' );

  CLEAR(pReader);

  /* Decode the base blockid, and set the cursor to the first term. */
  n = fts3GetVarint(pData+1, &pReader->iBlockid);
  assert( 1+n<=nData );
  pReader->pData = pData+1+n;
  pReader->nData = nData-(1+n);

  /* A single-child interior node (such as when a leaf node was too
  ** large for the segment directory) won't have any terms.
  ** Otherwise, decode the first term.
  */
  if( pReader->nData==0 ){
    dataBufferInit(&pReader->term, 0);
  }else{
    n = fts3GetVarint32(pReader->pData, &nTerm);
    dataBufferInit(&pReader->term, nTerm);
    dataBufferReplace(&pReader->term, pReader->pData+n, nTerm);
    assert( n+nTerm<=pReader->nData );
    pReader->pData += n+nTerm;
    pReader->nData -= n+nTerm;
  }
}

static int interiorReaderAtEnd(InteriorReader *pReader){
  return pReader->term.nData==0;
}

static sqlite_int64 interiorReaderCurrentBlockid(InteriorReader *pReader){
  return pReader->iBlockid;
}

static int interiorReaderTermBytes(InteriorReader *pReader){
  assert( !interiorReaderAtEnd(pReader) );
  return pReader->term.nData;
}
static const char *interiorReaderTerm(InteriorReader *pReader){
  assert( !interiorReaderAtEnd(pReader) );
  return pReader->term.pData;
}

/* Step forward to the next term in the node. */
static void interiorReaderStep(InteriorReader *pReader){
  assert( !interiorReaderAtEnd(pReader) );

  /* If the last term has been read, signal eof, else construct the
  ** next term.
  */
  if( pReader->nData==0 ){
    dataBufferReset(&pReader->term);
  }else{
    int n, nPrefix, nSuffix;

    n = fts3GetVarint32(pReader->pData, &nPrefix);
    n += fts3GetVarint32(pReader->pData+n, &nSuffix);

    /* Truncate the current term and append suffix data. */
    pReader->term.nData = nPrefix;
    dataBufferAppend(&pReader->term, pReader->pData+n, nSuffix);

    assert( n+nSuffix<=pReader->nData );
    pReader->pData += n+nSuffix;
    pReader->nData -= n+nSuffix;
  }
  pReader->iBlockid++;
}

/* Compare the current term to pTerm[nTerm], returning strcmp-style
** results.  If isPrefix, equality means equal through nTerm bytes.
*/
static int interiorReaderTermCmp(InteriorReader *pReader,
                                 const char *pTerm, int nTerm, int isPrefix){
  const char *pReaderTerm = interiorReaderTerm(pReader);
  int nReaderTerm = interiorReaderTermBytes(pReader);
  int c, n = nReaderTerm<nTerm ? nReaderTerm : nTerm;

  if( n==0 ){
    if( nReaderTerm>0 ) return -1;
    if( nTerm>0 ) return 1;
    return 0;
  }

  c = memcmp(pReaderTerm, pTerm, n);
  if( c!=0 ) return c;
  if( isPrefix && n==nTerm ) return 0;
  return nReaderTerm - nTerm;
}

/****************************************************************/
/* LeafWriter is used to collect terms and associated doclist data
** into leaf blocks in %_segments (see top of file for format info).
** Expected usage is:
**
** LeafWriter writer;
** leafWriterInit(0, 0, &writer);
** while( sorted_terms_left_to_process ){
**   // data is doclist data for that term.
**   rc = leafWriterStep(v, &writer, pTerm, nTerm, pData, nData);
**   if( rc!=SQLITE_OK ) goto err;
** }
** rc = leafWriterFinalize(v, &writer);
**err:
** leafWriterDestroy(&writer);
** return rc;
**
** leafWriterStep() may write a collected leaf out to %_segments.
** leafWriterFinalize() finishes writing any buffered data and stores
** a root node in %_segdir.  leafWriterDestroy() frees all buffers and
** InteriorWriters allocated as part of writing this segment.
**
** TODO(shess) Document leafWriterStepMerge().
*/

/* Put terms with data this big in their own block. */
#define STANDALONE_MIN 1024

/* Keep leaf blocks below this size. */
#define LEAF_MAX 2048

typedef struct LeafWriter {
  int iLevel;
  int idx;
  sqlite_int64 iStartBlockid;     /* needed to create the root info */
  sqlite_int64 iEndBlockid;       /* when we're done writing. */

  DataBuffer term;                /* previous encoded term */
  DataBuffer data;                /* encoding buffer */

  /* bytes of first term in the current node which distinguishes that
  ** term from the last term of the previous node.
  */
  int nTermDistinct;

  InteriorWriter parentWriter;    /* if we overflow */
  int has_parent;
} LeafWriter;

static void leafWriterInit(int iLevel, int idx, LeafWriter *pWriter){
  CLEAR(pWriter);
  pWriter->iLevel = iLevel;
  pWriter->idx = idx;

  dataBufferInit(&pWriter->term, 32);

  /* Start out with a reasonably sized block, though it can grow. */
  dataBufferInit(&pWriter->data, LEAF_MAX);
}

#ifndef NDEBUG
/* Verify that the data is readable as a leaf node. */
static void leafNodeValidate(const char *pData, int nData){
  int n, iDummy;

  if( nData==0 ) return;
  assert( nData>0 );
  assert( pData!=0 );
  assert( pData+nData>pData );

  /* Must lead with a varint(0) */
  n = fts3GetVarint32(pData, &iDummy);
  assert( iDummy==0 );
  assert( n>0 );
  assert( n<nData );
  pData += n;
  nData -= n;

  /* Leading term length and data must fit in buffer. */
  n = fts3GetVarint32(pData, &iDummy);
  assert( n>0 );
  assert( iDummy>0 );
  assert( n+iDummy>0 );
  assert( n+iDummy<nData );
  pData += n+iDummy;
  nData -= n+iDummy;

  /* Leading term's doclist length and data must fit. */
  n = fts3GetVarint32(pData, &iDummy);
  assert( n>0 );
  assert( iDummy>0 );
  assert( n+iDummy>0 );
  assert( n+iDummy<=nData );
  ASSERT_VALID_DOCLIST(DL_DEFAULT, pData+n, iDummy, NULL);
  pData += n+iDummy;
  nData -= n+iDummy;

  /* Verify that trailing terms and doclists also are readable. */
  while( nData!=0 ){
    n = fts3GetVarint32(pData, &iDummy);
    assert( n>0 );
    assert( iDummy>=0 );
    assert( n<nData );
    pData += n;
    nData -= n;
    n = fts3GetVarint32(pData, &iDummy);
    assert( n>0 );
    assert( iDummy>0 );
    assert( n+iDummy>0 );
    assert( n+iDummy<nData );
    pData += n+iDummy;
    nData -= n+iDummy;

    n = fts3GetVarint32(pData, &iDummy);
    assert( n>0 );
    assert( iDummy>0 );
    assert( n+iDummy>0 );
    assert( n+iDummy<=nData );
    ASSERT_VALID_DOCLIST(DL_DEFAULT, pData+n, iDummy, NULL);
    pData += n+iDummy;
    nData -= n+iDummy;
  }
}
#define ASSERT_VALID_LEAF_NODE(p, n) leafNodeValidate(p, n)
#else
#define ASSERT_VALID_LEAF_NODE(p, n) assert( 1 )
#endif

/* Flush the current leaf node to %_segments, and adding the resulting
** blockid and the starting term to the interior node which will
** contain it.
*/
static int leafWriterInternalFlush(fulltext_vtab *v, LeafWriter *pWriter,
                                   int iData, int nData){
  sqlite_int64 iBlockid = 0;
  const char *pStartingTerm;
  int nStartingTerm, rc, n;

  /* Must have the leading varint(0) flag, plus at least some
  ** valid-looking data.
  */
  assert( nData>2 );
  assert( iData>=0 );
  assert( iData+nData<=pWriter->data.nData );
  ASSERT_VALID_LEAF_NODE(pWriter->data.pData+iData, nData);

  rc = block_insert(v, pWriter->data.pData+iData, nData, &iBlockid);
  if( rc!=SQLITE_OK ) return rc;
  assert( iBlockid!=0 );

  /* Reconstruct the first term in the leaf for purposes of building
  ** the interior node.
  */
  n = fts3GetVarint32(pWriter->data.pData+iData+1, &nStartingTerm);
  pStartingTerm = pWriter->data.pData+iData+1+n;
  assert( pWriter->data.nData>iData+1+n+nStartingTerm );
  assert( pWriter->nTermDistinct>0 );
  assert( pWriter->nTermDistinct<=nStartingTerm );
  nStartingTerm = pWriter->nTermDistinct;

  if( pWriter->has_parent ){
    interiorWriterAppend(&pWriter->parentWriter,
                         pStartingTerm, nStartingTerm, iBlockid);
  }else{
    interiorWriterInit(1, pStartingTerm, nStartingTerm, iBlockid,
                       &pWriter->parentWriter);
    pWriter->has_parent = 1;
  }

  /* Track the span of this segment's leaf nodes. */
  if( pWriter->iEndBlockid==0 ){
    pWriter->iEndBlockid = pWriter->iStartBlockid = iBlockid;
  }else{
    pWriter->iEndBlockid++;
    assert( iBlockid==pWriter->iEndBlockid );
  }

  return SQLITE_OK;
}
static int leafWriterFlush(fulltext_vtab *v, LeafWriter *pWriter){
  int rc = leafWriterInternalFlush(v, pWriter, 0, pWriter->data.nData);
  if( rc!=SQLITE_OK ) return rc;

  /* Re-initialize the output buffer. */
  dataBufferReset(&pWriter->data);

  return SQLITE_OK;
}

/* Fetch the root info for the segment.  If the entire leaf fits
** within ROOT_MAX, then it will be returned directly, otherwise it
** will be flushed and the root info will be returned from the
** interior node.  *piEndBlockid is set to the blockid of the last
** interior or leaf node written to disk (0 if none are written at
** all).
*/
static int leafWriterRootInfo(fulltext_vtab *v, LeafWriter *pWriter,
                              char **ppRootInfo, int *pnRootInfo,
                              sqlite_int64 *piEndBlockid){
  /* we can fit the segment entirely inline */
  if( !pWriter->has_parent && pWriter->data.nData<ROOT_MAX ){
    *ppRootInfo = pWriter->data.pData;
    *pnRootInfo = pWriter->data.nData;
    *piEndBlockid = 0;
    return SQLITE_OK;
  }

  /* Flush remaining leaf data. */
  if( pWriter->data.nData>0 ){
    int rc = leafWriterFlush(v, pWriter);
    if( rc!=SQLITE_OK ) return rc;
  }

  /* We must have flushed a leaf at some point. */
  assert( pWriter->has_parent );

  /* Tenatively set the end leaf blockid as the end blockid.  If the
  ** interior node can be returned inline, this will be the final
  ** blockid, otherwise it will be overwritten by
  ** interiorWriterRootInfo().
  */
  *piEndBlockid = pWriter->iEndBlockid;

  return interiorWriterRootInfo(v, &pWriter->parentWriter,
                                ppRootInfo, pnRootInfo, piEndBlockid);
}

/* Collect the rootInfo data and store it into the segment directory.
** This has the effect of flushing the segment's leaf data to
** %_segments, and also flushing any interior nodes to %_segments.
*/
static int leafWriterFinalize(fulltext_vtab *v, LeafWriter *pWriter){
  sqlite_int64 iEndBlockid;
  char *pRootInfo;
  int rc, nRootInfo;

  rc = leafWriterRootInfo(v, pWriter, &pRootInfo, &nRootInfo, &iEndBlockid);
  if( rc!=SQLITE_OK ) return rc;

  /* Don't bother storing an entirely empty segment. */
  if( iEndBlockid==0 && nRootInfo==0 ) return SQLITE_OK;

  return segdir_set(v, pWriter->iLevel, pWriter->idx,
                    pWriter->iStartBlockid, pWriter->iEndBlockid,
                    iEndBlockid, pRootInfo, nRootInfo);
}

static void leafWriterDestroy(LeafWriter *pWriter){
  if( pWriter->has_parent ) interiorWriterDestroy(&pWriter->parentWriter);
  dataBufferDestroy(&pWriter->term);
  dataBufferDestroy(&pWriter->data);
}

/* Encode a term into the leafWriter, delta-encoding as appropriate.
** Returns the length of the new term which distinguishes it from the
** previous term, which can be used to set nTermDistinct when a node
** boundary is crossed.
*/
static int leafWriterEncodeTerm(LeafWriter *pWriter,
                                const char *pTerm, int nTerm){
  char c[VARINT_MAX+VARINT_MAX];
  int n, nPrefix = 0;

  assert( nTerm>0 );
  while( nPrefix<pWriter->term.nData &&
         pTerm[nPrefix]==pWriter->term.pData[nPrefix] ){
    nPrefix++;
    /* Failing this implies that the terms weren't in order. */
    assert( nPrefix<nTerm );
  }

  if( pWriter->data.nData==0 ){
    /* Encode the node header and leading term as:
    **  varint(0)
    **  varint(nTerm)
    **  char pTerm[nTerm]
    */
    n = fts3PutVarint(c, '\0');
    n += fts3PutVarint(c+n, nTerm);
    dataBufferAppend2(&pWriter->data, c, n, pTerm, nTerm);
  }else{
    /* Delta-encode the term as:
    **  varint(nPrefix)
    **  varint(nSuffix)
    **  char pTermSuffix[nSuffix]
    */
    n = fts3PutVarint(c, nPrefix);
    n += fts3PutVarint(c+n, nTerm-nPrefix);
    dataBufferAppend2(&pWriter->data, c, n, pTerm+nPrefix, nTerm-nPrefix);
  }
  dataBufferReplace(&pWriter->term, pTerm, nTerm);

  return nPrefix+1;
}

/* Used to avoid a memmove when a large amount of doclist data is in
** the buffer.  This constructs a node and term header before
** iDoclistData and flushes the resulting complete node using
** leafWriterInternalFlush().
*/
static int leafWriterInlineFlush(fulltext_vtab *v, LeafWriter *pWriter,
                                 const char *pTerm, int nTerm,
                                 int iDoclistData){
  char c[VARINT_MAX+VARINT_MAX];
  int iData, n = fts3PutVarint(c, 0);
  n += fts3PutVarint(c+n, nTerm);

  /* There should always be room for the header.  Even if pTerm shared
  ** a substantial prefix with the previous term, the entire prefix
  ** could be constructed from earlier data in the doclist, so there
  ** should be room.
  */
  assert( iDoclistData>=n+nTerm );

  iData = iDoclistData-(n+nTerm);
  memcpy(pWriter->data.pData+iData, c, n);
  memcpy(pWriter->data.pData+iData+n, pTerm, nTerm);

  return leafWriterInternalFlush(v, pWriter, iData, pWriter->data.nData-iData);
}

/* Push pTerm[nTerm] along with the doclist data to the leaf layer of
** %_segments.
*/
static int leafWriterStepMerge(fulltext_vtab *v, LeafWriter *pWriter,
                               const char *pTerm, int nTerm,
                               DLReader *pReaders, int nReaders){
  char c[VARINT_MAX+VARINT_MAX];
  int iTermData = pWriter->data.nData, iDoclistData;
  int i, nData, n, nActualData, nActual, rc, nTermDistinct;

  ASSERT_VALID_LEAF_NODE(pWriter->data.pData, pWriter->data.nData);
  nTermDistinct = leafWriterEncodeTerm(pWriter, pTerm, nTerm);

  /* Remember nTermDistinct if opening a new node. */
  if( iTermData==0 ) pWriter->nTermDistinct = nTermDistinct;

  iDoclistData = pWriter->data.nData;

  /* Estimate the length of the merged doclist so we can leave space
  ** to encode it.
  */
  for(i=0, nData=0; i<nReaders; i++){
    nData += dlrAllDataBytes(&pReaders[i]);
  }
  n = fts3PutVarint(c, nData);
  dataBufferAppend(&pWriter->data, c, n);

  docListMerge(&pWriter->data, pReaders, nReaders);
  ASSERT_VALID_DOCLIST(DL_DEFAULT,
                       pWriter->data.pData+iDoclistData+n,
                       pWriter->data.nData-iDoclistData-n, NULL);

  /* The actual amount of doclist data at this point could be smaller
  ** than the length we encoded.  Additionally, the space required to
  ** encode this length could be smaller.  For small doclists, this is
  ** not a big deal, we can just use memmove() to adjust things.
  */
  nActualData = pWriter->data.nData-(iDoclistData+n);
  nActual = fts3PutVarint(c, nActualData);
  assert( nActualData<=nData );
  assert( nActual<=n );

  /* If the new doclist is big enough for force a standalone leaf
  ** node, we can immediately flush it inline without doing the
  ** memmove().
  */
  /* TODO(shess) This test matches leafWriterStep(), which does this
  ** test before it knows the cost to varint-encode the term and
  ** doclist lengths.  At some point, change to
  ** pWriter->data.nData-iTermData>STANDALONE_MIN.
  */
  if( nTerm+nActualData>STANDALONE_MIN ){
    /* Push leaf node from before this term. */
    if( iTermData>0 ){
      rc = leafWriterInternalFlush(v, pWriter, 0, iTermData);
      if( rc!=SQLITE_OK ) return rc;

      pWriter->nTermDistinct = nTermDistinct;
    }

    /* Fix the encoded doclist length. */
    iDoclistData += n - nActual;
    memcpy(pWriter->data.pData+iDoclistData, c, nActual);

    /* Push the standalone leaf node. */
    rc = leafWriterInlineFlush(v, pWriter, pTerm, nTerm, iDoclistData);
    if( rc!=SQLITE_OK ) return rc;

    /* Leave the node empty. */
    dataBufferReset(&pWriter->data);

    return rc;
  }

  /* At this point, we know that the doclist was small, so do the
  ** memmove if indicated.
  */
  if( nActual<n ){
    memmove(pWriter->data.pData+iDoclistData+nActual,
            pWriter->data.pData+iDoclistData+n,
            pWriter->data.nData-(iDoclistData+n));
    pWriter->data.nData -= n-nActual;
  }

  /* Replace written length with actual length. */
  memcpy(pWriter->data.pData+iDoclistData, c, nActual);

  /* If the node is too large, break things up. */
  /* TODO(shess) This test matches leafWriterStep(), which does this
  ** test before it knows the cost to varint-encode the term and
  ** doclist lengths.  At some point, change to
  ** pWriter->data.nData>LEAF_MAX.
  */
  if( iTermData+nTerm+nActualData>LEAF_MAX ){
    /* Flush out the leading data as a node */
    rc = leafWriterInternalFlush(v, pWriter, 0, iTermData);
    if( rc!=SQLITE_OK ) return rc;

    pWriter->nTermDistinct = nTermDistinct;

    /* Rebuild header using the current term */
    n = fts3PutVarint(pWriter->data.pData, 0);
    n += fts3PutVarint(pWriter->data.pData+n, nTerm);
    memcpy(pWriter->data.pData+n, pTerm, nTerm);
    n += nTerm;

    /* There should always be room, because the previous encoding
    ** included all data necessary to construct the term.
    */
    assert( n<iDoclistData );
    /* So long as STANDALONE_MIN is half or less of LEAF_MAX, the
    ** following memcpy() is safe (as opposed to needing a memmove).
    */
    assert( 2*STANDALONE_MIN<=LEAF_MAX );
    assert( n+pWriter->data.nData-iDoclistData<iDoclistData );
    memcpy(pWriter->data.pData+n,
           pWriter->data.pData+iDoclistData,
           pWriter->data.nData-iDoclistData);
    pWriter->data.nData -= iDoclistData-n;
  }
  ASSERT_VALID_LEAF_NODE(pWriter->data.pData, pWriter->data.nData);

  return SQLITE_OK;
}

/* Push pTerm[nTerm] along with the doclist data to the leaf layer of
** %_segments.
*/
/* TODO(shess) Revise writeZeroSegment() so that doclists are
** constructed directly in pWriter->data.
*/
static int leafWriterStep(fulltext_vtab *v, LeafWriter *pWriter,
                          const char *pTerm, int nTerm,
                          const char *pData, int nData){
  int rc;
  DLReader reader;

  dlrInit(&reader, DL_DEFAULT, pData, nData);
  rc = leafWriterStepMerge(v, pWriter, pTerm, nTerm, &reader, 1);
  dlrDestroy(&reader);

  return rc;
}


/****************************************************************/
/* LeafReader is used to iterate over an individual leaf node. */
typedef struct LeafReader {
  DataBuffer term;          /* copy of current term. */

  const char *pData;        /* data for current term. */
  int nData;
} LeafReader;

static void leafReaderDestroy(LeafReader *pReader){
  dataBufferDestroy(&pReader->term);
  SCRAMBLE(pReader);
}

static int leafReaderAtEnd(LeafReader *pReader){
  return pReader->nData<=0;
}

/* Access the current term. */
static int leafReaderTermBytes(LeafReader *pReader){
  return pReader->term.nData;
}
static const char *leafReaderTerm(LeafReader *pReader){
  assert( pReader->term.nData>0 );
  return pReader->term.pData;
}

/* Access the doclist data for the current term. */
static int leafReaderDataBytes(LeafReader *pReader){
  int nData;
  assert( pReader->term.nData>0 );
  fts3GetVarint32(pReader->pData, &nData);
  return nData;
}
static const char *leafReaderData(LeafReader *pReader){
  int n, nData;
  assert( pReader->term.nData>0 );
  n = fts3GetVarint32(pReader->pData, &nData);
  return pReader->pData+n;
}

static void leafReaderInit(const char *pData, int nData,
                           LeafReader *pReader){
  int nTerm, n;

  assert( nData>0 );
  assert( pData[0]=='\0' );

  CLEAR(pReader);

  /* Read the first term, skipping the header byte. */
  n = fts3GetVarint32(pData+1, &nTerm);
  dataBufferInit(&pReader->term, nTerm);
  dataBufferReplace(&pReader->term, pData+1+n, nTerm);

  /* Position after the first term. */
  assert( 1+n+nTerm<nData );
  pReader->pData = pData+1+n+nTerm;
  pReader->nData = nData-1-n-nTerm;
}

/* Step the reader forward to the next term. */
static void leafReaderStep(LeafReader *pReader){
  int n, nData, nPrefix, nSuffix;
  assert( !leafReaderAtEnd(pReader) );

  /* Skip previous entry's data block. */
  n = fts3GetVarint32(pReader->pData, &nData);
  assert( n+nData<=pReader->nData );
  pReader->pData += n+nData;
  pReader->nData -= n+nData;

  if( !leafReaderAtEnd(pReader) ){
    /* Construct the new term using a prefix from the old term plus a
    ** suffix from the leaf data.
    */
    n = fts3GetVarint32(pReader->pData, &nPrefix);
    n += fts3GetVarint32(pReader->pData+n, &nSuffix);
    assert( n+nSuffix<pReader->nData );
    pReader->term.nData = nPrefix;
    dataBufferAppend(&pReader->term, pReader->pData+n, nSuffix);

    pReader->pData += n+nSuffix;
    pReader->nData -= n+nSuffix;
  }
}

/* strcmp-style comparison of pReader's current term against pTerm.
** If isPrefix, equality means equal through nTerm bytes.
*/
static int leafReaderTermCmp(LeafReader *pReader,
                             const char *pTerm, int nTerm, int isPrefix){
  int c, n = pReader->term.nData<nTerm ? pReader->term.nData : nTerm;
  if( n==0 ){
    if( pReader->term.nData>0 ) return -1;
    if(nTerm>0 ) return 1;
    return 0;
  }

  c = memcmp(pReader->term.pData, pTerm, n);
  if( c!=0 ) return c;
  if( isPrefix && n==nTerm ) return 0;
  return pReader->term.nData - nTerm;
}


/****************************************************************/
/* LeavesReader wraps LeafReader to allow iterating over the entire
** leaf layer of the tree.
*/
typedef struct LeavesReader {
  int idx;                  /* Index within the segment. */

  sqlite3_stmt *pStmt;      /* Statement we're streaming leaves from. */
  int eof;                  /* we've seen SQLITE_DONE from pStmt. */

  LeafReader leafReader;    /* reader for the current leaf. */
  DataBuffer rootData;      /* root data for inline. */
} LeavesReader;

/* Access the current term. */
static int leavesReaderTermBytes(LeavesReader *pReader){
  assert( !pReader->eof );
  return leafReaderTermBytes(&pReader->leafReader);
}
static const char *leavesReaderTerm(LeavesReader *pReader){
  assert( !pReader->eof );
  return leafReaderTerm(&pReader->leafReader);
}

/* Access the doclist data for the current term. */
static int leavesReaderDataBytes(LeavesReader *pReader){
  assert( !pReader->eof );
  return leafReaderDataBytes(&pReader->leafReader);
}
static const char *leavesReaderData(LeavesReader *pReader){
  assert( !pReader->eof );
  return leafReaderData(&pReader->leafReader);
}

static int leavesReaderAtEnd(LeavesReader *pReader){
  return pReader->eof;
}

/* loadSegmentLeaves() may not read all the way to SQLITE_DONE, thus
** leaving the statement handle open, which locks the table.
*/
/* TODO(shess) This "solution" is not satisfactory.  Really, there
** should be check-in function for all statement handles which
** arranges to call sqlite3_reset().  This most likely will require
** modification to control flow all over the place, though, so for now
** just punt.
**
** Note the the current system assumes that segment merges will run to
** completion, which is why this particular probably hasn't arisen in
** this case.  Probably a brittle assumption.
*/
static int leavesReaderReset(LeavesReader *pReader){
  return sqlite3_reset(pReader->pStmt);
}

static void leavesReaderDestroy(LeavesReader *pReader){
  /* If idx is -1, that means we're using a non-cached statement
  ** handle in the optimize() case, so we need to release it.
  */
  if( pReader->pStmt!=NULL && pReader->idx==-1 ){
    sqlite3_finalize(pReader->pStmt);
  }
  leafReaderDestroy(&pReader->leafReader);
  dataBufferDestroy(&pReader->rootData);
  SCRAMBLE(pReader);
}

/* Initialize pReader with the given root data (if iStartBlockid==0
** the leaf data was entirely contained in the root), or from the
** stream of blocks between iStartBlockid and iEndBlockid, inclusive.
*/
static int leavesReaderInit(fulltext_vtab *v,
                            int idx,
                            sqlite_int64 iStartBlockid,
                            sqlite_int64 iEndBlockid,
                            const char *pRootData, int nRootData,
                            LeavesReader *pReader){
  CLEAR(pReader);
  pReader->idx = idx;

  dataBufferInit(&pReader->rootData, 0);
  if( iStartBlockid==0 ){
    /* Entire leaf level fit in root data. */
    dataBufferReplace(&pReader->rootData, pRootData, nRootData);
    leafReaderInit(pReader->rootData.pData, pReader->rootData.nData,
                   &pReader->leafReader);
  }else{
    sqlite3_stmt *s;
    int rc = sql_get_leaf_statement(v, idx, &s);
    if( rc!=SQLITE_OK ) return rc;

    rc = sqlite3_bind_int64(s, 1, iStartBlockid);
    if( rc!=SQLITE_OK ) return rc;

    rc = sqlite3_bind_int64(s, 2, iEndBlockid);
    if( rc!=SQLITE_OK ) return rc;

    rc = sqlite3_step(s);
    if( rc==SQLITE_DONE ){
      pReader->eof = 1;
      return SQLITE_OK;
    }
    if( rc!=SQLITE_ROW ) return rc;

    pReader->pStmt = s;
    leafReaderInit(sqlite3_column_blob(pReader->pStmt, 0),
                   sqlite3_column_bytes(pReader->pStmt, 0),
                   &pReader->leafReader);
  }
  return SQLITE_OK;
}

/* Step the current leaf forward to the next term.  If we reach the
** end of the current leaf, step forward to the next leaf block.
*/
static int leavesReaderStep(fulltext_vtab *v, LeavesReader *pReader){
  assert( !leavesReaderAtEnd(pReader) );
  leafReaderStep(&pReader->leafReader);

  if( leafReaderAtEnd(&pReader->leafReader) ){
    int rc;
    if( pReader->rootData.pData ){
      pReader->eof = 1;
      return SQLITE_OK;
    }
    rc = sqlite3_step(pReader->pStmt);
    if( rc!=SQLITE_ROW ){
      pReader->eof = 1;
      return rc==SQLITE_DONE ? SQLITE_OK : rc;
    }
    leafReaderDestroy(&pReader->leafReader);
    leafReaderInit(sqlite3_column_blob(pReader->pStmt, 0),
                   sqlite3_column_bytes(pReader->pStmt, 0),
                   &pReader->leafReader);
  }
  return SQLITE_OK;
}

/* Order LeavesReaders by their term, ignoring idx.  Readers at eof
** always sort to the end.
*/
static int leavesReaderTermCmp(LeavesReader *lr1, LeavesReader *lr2){
  if( leavesReaderAtEnd(lr1) ){
    if( leavesReaderAtEnd(lr2) ) return 0;
    return 1;
  }
  if( leavesReaderAtEnd(lr2) ) return -1;

  return leafReaderTermCmp(&lr1->leafReader,
                           leavesReaderTerm(lr2), leavesReaderTermBytes(lr2),
                           0);
}

/* Similar to leavesReaderTermCmp(), with additional ordering by idx
** so that older segments sort before newer segments.
*/
static int leavesReaderCmp(LeavesReader *lr1, LeavesReader *lr2){
  int c = leavesReaderTermCmp(lr1, lr2);
  if( c!=0 ) return c;
  return lr1->idx-lr2->idx;
}

/* Assume that pLr[1]..pLr[nLr] are sorted.  Bubble pLr[0] into its
** sorted position.
*/
static void leavesReaderReorder(LeavesReader *pLr, int nLr){
  while( nLr>1 && leavesReaderCmp(pLr, pLr+1)>0 ){
    LeavesReader tmp = pLr[0];
    pLr[0] = pLr[1];
    pLr[1] = tmp;
    nLr--;
    pLr++;
  }
}

/* Initializes pReaders with the segments from level iLevel, returning
** the number of segments in *piReaders.  Leaves pReaders in sorted
** order.
*/
static int leavesReadersInit(fulltext_vtab *v, int iLevel,
                             LeavesReader *pReaders, int *piReaders){
  sqlite3_stmt *s;
  int i, rc = sql_get_statement(v, SEGDIR_SELECT_LEVEL_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  i = 0;
  while( (rc = sqlite3_step(s))==SQLITE_ROW ){
    sqlite_int64 iStart = sqlite3_column_int64(s, 0);
    sqlite_int64 iEnd = sqlite3_column_int64(s, 1);
    const char *pRootData = sqlite3_column_blob(s, 2);
    int nRootData = sqlite3_column_bytes(s, 2);

    assert( i<MERGE_COUNT );
    rc = leavesReaderInit(v, i, iStart, iEnd, pRootData, nRootData,
                          &pReaders[i]);
    if( rc!=SQLITE_OK ) break;

    i++;
  }
  if( rc!=SQLITE_DONE ){
    while( i-->0 ){
      leavesReaderDestroy(&pReaders[i]);
    }
    return rc;
  }

  *piReaders = i;

  /* Leave our results sorted by term, then age. */
  while( i-- ){
    leavesReaderReorder(pReaders+i, *piReaders-i);
  }
  return SQLITE_OK;
}

/* Merge doclists from pReaders[nReaders] into a single doclist, which
** is written to pWriter.  Assumes pReaders is ordered oldest to
** newest.
*/
/* TODO(shess) Consider putting this inline in segmentMerge(). */
static int leavesReadersMerge(fulltext_vtab *v,
                              LeavesReader *pReaders, int nReaders,
                              LeafWriter *pWriter){
  DLReader dlReaders[MERGE_COUNT];
  const char *pTerm = leavesReaderTerm(pReaders);
  int i, nTerm = leavesReaderTermBytes(pReaders);

  assert( nReaders<=MERGE_COUNT );

  for(i=0; i<nReaders; i++){
    dlrInit(&dlReaders[i], DL_DEFAULT,
            leavesReaderData(pReaders+i),
            leavesReaderDataBytes(pReaders+i));
  }

  return leafWriterStepMerge(v, pWriter, pTerm, nTerm, dlReaders, nReaders);
}

/* Forward ref due to mutual recursion with segdirNextIndex(). */
static int segmentMerge(fulltext_vtab *v, int iLevel);

/* Put the next available index at iLevel into *pidx.  If iLevel
** already has MERGE_COUNT segments, they are merged to a higher
** level to make room.
*/
static int segdirNextIndex(fulltext_vtab *v, int iLevel, int *pidx){
  int rc = segdir_max_index(v, iLevel, pidx);
  if( rc==SQLITE_DONE ){              /* No segments at iLevel. */
    *pidx = 0;
  }else if( rc==SQLITE_ROW ){
    if( *pidx==(MERGE_COUNT-1) ){
      rc = segmentMerge(v, iLevel);
      if( rc!=SQLITE_OK ) return rc;
      *pidx = 0;
    }else{
      (*pidx)++;
    }
  }else{
    return rc;
  }
  return SQLITE_OK;
}

/* Merge MERGE_COUNT segments at iLevel into a new segment at
** iLevel+1.  If iLevel+1 is already full of segments, those will be
** merged to make room.
*/
static int segmentMerge(fulltext_vtab *v, int iLevel){
  LeafWriter writer;
  LeavesReader lrs[MERGE_COUNT];
  int i, rc, idx = 0;

  /* Determine the next available segment index at the next level,
  ** merging as necessary.
  */
  rc = segdirNextIndex(v, iLevel+1, &idx);
  if( rc!=SQLITE_OK ) return rc;

  /* TODO(shess) This assumes that we'll always see exactly
  ** MERGE_COUNT segments to merge at a given level.  That will be
  ** broken if we allow the developer to request preemptive or
  ** deferred merging.
  */
  memset(&lrs, '\0', sizeof(lrs));
  rc = leavesReadersInit(v, iLevel, lrs, &i);
  if( rc!=SQLITE_OK ) return rc;
  assert( i==MERGE_COUNT );

  leafWriterInit(iLevel+1, idx, &writer);

  /* Since leavesReaderReorder() pushes readers at eof to the end,
  ** when the first reader is empty, all will be empty.
  */
  while( !leavesReaderAtEnd(lrs) ){
    /* Figure out how many readers share their next term. */
    for(i=1; i<MERGE_COUNT && !leavesReaderAtEnd(lrs+i); i++){
      if( 0!=leavesReaderTermCmp(lrs, lrs+i) ) break;
    }

    rc = leavesReadersMerge(v, lrs, i, &writer);
    if( rc!=SQLITE_OK ) goto err;

    /* Step forward those that were merged. */
    while( i-->0 ){
      rc = leavesReaderStep(v, lrs+i);
      if( rc!=SQLITE_OK ) goto err;

      /* Reorder by term, then by age. */
      leavesReaderReorder(lrs+i, MERGE_COUNT-i);
    }
  }

  for(i=0; i<MERGE_COUNT; i++){
    leavesReaderDestroy(&lrs[i]);
  }

  rc = leafWriterFinalize(v, &writer);
  leafWriterDestroy(&writer);
  if( rc!=SQLITE_OK ) return rc;

  /* Delete the merged segment data. */
  return segdir_delete(v, iLevel);

 err:
  for(i=0; i<MERGE_COUNT; i++){
    leavesReaderDestroy(&lrs[i]);
  }
  leafWriterDestroy(&writer);
  return rc;
}

/* Accumulate the union of *acc and *pData into *acc. */
static void docListAccumulateUnion(DataBuffer *acc,
                                   const char *pData, int nData) {
  DataBuffer tmp = *acc;
  dataBufferInit(acc, tmp.nData+nData);
  docListUnion(tmp.pData, tmp.nData, pData, nData, acc);
  dataBufferDestroy(&tmp);
}

/* TODO(shess) It might be interesting to explore different merge
** strategies, here.  For instance, since this is a sorted merge, we
** could easily merge many doclists in parallel.  With some
** comprehension of the storage format, we could merge all of the
** doclists within a leaf node directly from the leaf node's storage.
** It may be worthwhile to merge smaller doclists before larger
** doclists, since they can be traversed more quickly - but the
** results may have less overlap, making them more expensive in a
** different way.
*/

/* Scan pReader for pTerm/nTerm, and merge the term's doclist over
** *out (any doclists with duplicate docids overwrite those in *out).
** Internal function for loadSegmentLeaf().
*/
static int loadSegmentLeavesInt(fulltext_vtab *v, LeavesReader *pReader,
                                const char *pTerm, int nTerm, int isPrefix,
                                DataBuffer *out){
  /* doclist data is accumulated into pBuffers similar to how one does
  ** increment in binary arithmetic.  If index 0 is empty, the data is
  ** stored there.  If there is data there, it is merged and the
  ** results carried into position 1, with further merge-and-carry
  ** until an empty position is found.
  */
  DataBuffer *pBuffers = NULL;
  int nBuffers = 0, nMaxBuffers = 0, rc;

  assert( nTerm>0 );

  for(rc=SQLITE_OK; rc==SQLITE_OK && !leavesReaderAtEnd(pReader);
      rc=leavesReaderStep(v, pReader)){
    /* TODO(shess) Really want leavesReaderTermCmp(), but that name is
    ** already taken to compare the terms of two LeavesReaders.  Think
    ** on a better name.  [Meanwhile, break encapsulation rather than
    ** use a confusing name.]
    */
    int c = leafReaderTermCmp(&pReader->leafReader, pTerm, nTerm, isPrefix);
    if( c>0 ) break;      /* Past any possible matches. */
    if( c==0 ){
      const char *pData = leavesReaderData(pReader);
      int iBuffer, nData = leavesReaderDataBytes(pReader);

      /* Find the first empty buffer. */
      for(iBuffer=0; iBuffer<nBuffers; ++iBuffer){
        if( 0==pBuffers[iBuffer].nData ) break;
      }

      /* Out of buffers, add an empty one. */
      if( iBuffer==nBuffers ){
        if( nBuffers==nMaxBuffers ){
          DataBuffer *p;
          nMaxBuffers += 20;

          /* Manual realloc so we can handle NULL appropriately. */
          p = sqlite3_malloc(nMaxBuffers*sizeof(*pBuffers));
          if( p==NULL ){
            rc = SQLITE_NOMEM;
            break;
          }

          if( nBuffers>0 ){
            assert(pBuffers!=NULL);
            memcpy(p, pBuffers, nBuffers*sizeof(*pBuffers));
            sqlite3_free(pBuffers);
          }
          pBuffers = p;
        }
        dataBufferInit(&(pBuffers[nBuffers]), 0);
        nBuffers++;
      }

      /* At this point, must have an empty at iBuffer. */
      assert(iBuffer<nBuffers && pBuffers[iBuffer].nData==0);

      /* If empty was first buffer, no need for merge logic. */
      if( iBuffer==0 ){
        dataBufferReplace(&(pBuffers[0]), pData, nData);
      }else{
        /* pAcc is the empty buffer the merged data will end up in. */
        DataBuffer *pAcc = &(pBuffers[iBuffer]);
        DataBuffer *p = &(pBuffers[0]);

        /* Handle position 0 specially to avoid need to prime pAcc
        ** with pData/nData.
        */
        dataBufferSwap(p, pAcc);
        docListAccumulateUnion(pAcc, pData, nData);

        /* Accumulate remaining doclists into pAcc. */
        for(++p; p<pAcc; ++p){
          docListAccumulateUnion(pAcc, p->pData, p->nData);

          /* dataBufferReset() could allow a large doclist to blow up
          ** our memory requirements.
          */
          if( p->nCapacity<1024 ){
            dataBufferReset(p);
          }else{
            dataBufferDestroy(p);
            dataBufferInit(p, 0);
          }
        }
      }
    }
  }

  /* Union all the doclists together into *out. */
  /* TODO(shess) What if *out is big?  Sigh. */
  if( rc==SQLITE_OK && nBuffers>0 ){
    int iBuffer;
    for(iBuffer=0; iBuffer<nBuffers; ++iBuffer){
      if( pBuffers[iBuffer].nData>0 ){
        if( out->nData==0 ){
          dataBufferSwap(out, &(pBuffers[iBuffer]));
        }else{
          docListAccumulateUnion(out, pBuffers[iBuffer].pData,
                                 pBuffers[iBuffer].nData);
        }
      }
    }
  }

  while( nBuffers-- ){
    dataBufferDestroy(&(pBuffers[nBuffers]));
  }
  if( pBuffers!=NULL ) sqlite3_free(pBuffers);

  return rc;
}

/* Call loadSegmentLeavesInt() with pData/nData as input. */
static int loadSegmentLeaf(fulltext_vtab *v, const char *pData, int nData,
                           const char *pTerm, int nTerm, int isPrefix,
                           DataBuffer *out){
  LeavesReader reader;
  int rc;

  assert( nData>1 );
  assert( *pData=='\0' );
  rc = leavesReaderInit(v, 0, 0, 0, pData, nData, &reader);
  if( rc!=SQLITE_OK ) return rc;

  rc = loadSegmentLeavesInt(v, &reader, pTerm, nTerm, isPrefix, out);
  leavesReaderReset(&reader);
  leavesReaderDestroy(&reader);
  return rc;
}

/* Call loadSegmentLeavesInt() with the leaf nodes from iStartLeaf to
** iEndLeaf (inclusive) as input, and merge the resulting doclist into
** out.
*/
static int loadSegmentLeaves(fulltext_vtab *v,
                             sqlite_int64 iStartLeaf, sqlite_int64 iEndLeaf,
                             const char *pTerm, int nTerm, int isPrefix,
                             DataBuffer *out){
  int rc;
  LeavesReader reader;

  assert( iStartLeaf<=iEndLeaf );
  rc = leavesReaderInit(v, 0, iStartLeaf, iEndLeaf, NULL, 0, &reader);
  if( rc!=SQLITE_OK ) return rc;

  rc = loadSegmentLeavesInt(v, &reader, pTerm, nTerm, isPrefix, out);
  leavesReaderReset(&reader);
  leavesReaderDestroy(&reader);
  return rc;
}

/* Taking pData/nData as an interior node, find the sequence of child
** nodes which could include pTerm/nTerm/isPrefix.  Note that the
** interior node terms logically come between the blocks, so there is
** one more blockid than there are terms (that block contains terms >=
** the last interior-node term).
*/
/* TODO(shess) The calling code may already know that the end child is
** not worth calculating, because the end may be in a later sibling
** node.  Consider whether breaking symmetry is worthwhile.  I suspect
** it is not worthwhile.
*/
static void getChildrenContaining(const char *pData, int nData,
                                  const char *pTerm, int nTerm, int isPrefix,
                                  sqlite_int64 *piStartChild,
                                  sqlite_int64 *piEndChild){
  InteriorReader reader;

  assert( nData>1 );
  assert( *pData!='\0' );
  interiorReaderInit(pData, nData, &reader);

  /* Scan for the first child which could contain pTerm/nTerm. */
  while( !interiorReaderAtEnd(&reader) ){
    if( interiorReaderTermCmp(&reader, pTerm, nTerm, 0)>0 ) break;
    interiorReaderStep(&reader);
  }
  *piStartChild = interiorReaderCurrentBlockid(&reader);

  /* Keep scanning to find a term greater than our term, using prefix
  ** comparison if indicated.  If isPrefix is false, this will be the
  ** same blockid as the starting block.
  */
  while( !interiorReaderAtEnd(&reader) ){
    if( interiorReaderTermCmp(&reader, pTerm, nTerm, isPrefix)>0 ) break;
    interiorReaderStep(&reader);
  }
  *piEndChild = interiorReaderCurrentBlockid(&reader);

  interiorReaderDestroy(&reader);

  /* Children must ascend, and if !prefix, both must be the same. */
  assert( *piEndChild>=*piStartChild );
  assert( isPrefix || *piStartChild==*piEndChild );
}

/* Read block at iBlockid and pass it with other params to
** getChildrenContaining().
*/
static int loadAndGetChildrenContaining(
  fulltext_vtab *v,
  sqlite_int64 iBlockid,
  const char *pTerm, int nTerm, int isPrefix,
  sqlite_int64 *piStartChild, sqlite_int64 *piEndChild
){
  sqlite3_stmt *s = NULL;
  int rc;

  assert( iBlockid!=0 );
  assert( pTerm!=NULL );
  assert( nTerm!=0 );        /* TODO(shess) Why not allow this? */
  assert( piStartChild!=NULL );
  assert( piEndChild!=NULL );

  rc = sql_get_statement(v, BLOCK_SELECT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_step(s);
  if( rc==SQLITE_DONE ) return SQLITE_ERROR;
  if( rc!=SQLITE_ROW ) return rc;

  getChildrenContaining(sqlite3_column_blob(s, 0), sqlite3_column_bytes(s, 0),
                        pTerm, nTerm, isPrefix, piStartChild, piEndChild);

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain
   * locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  if( rc!=SQLITE_DONE ) return rc;

  return SQLITE_OK;
}

/* Traverse the tree represented by pData[nData] looking for
** pTerm[nTerm], placing its doclist into *out.  This is internal to
** loadSegment() to make error-handling cleaner.
*/
static int loadSegmentInt(fulltext_vtab *v, const char *pData, int nData,
                          sqlite_int64 iLeavesEnd,
                          const char *pTerm, int nTerm, int isPrefix,
                          DataBuffer *out){
  /* Special case where root is a leaf. */
  if( *pData=='\0' ){
    return loadSegmentLeaf(v, pData, nData, pTerm, nTerm, isPrefix, out);
  }else{
    int rc;
    sqlite_int64 iStartChild, iEndChild;

    /* Process pData as an interior node, then loop down the tree
    ** until we find the set of leaf nodes to scan for the term.
    */
    getChildrenContaining(pData, nData, pTerm, nTerm, isPrefix,
                          &iStartChild, &iEndChild);
    while( iStartChild>iLeavesEnd ){
      sqlite_int64 iNextStart, iNextEnd;
      rc = loadAndGetChildrenContaining(v, iStartChild, pTerm, nTerm, isPrefix,
                                        &iNextStart, &iNextEnd);
      if( rc!=SQLITE_OK ) return rc;

      /* If we've branched, follow the end branch, too. */
      if( iStartChild!=iEndChild ){
        sqlite_int64 iDummy;
        rc = loadAndGetChildrenContaining(v, iEndChild, pTerm, nTerm, isPrefix,
                                          &iDummy, &iNextEnd);
        if( rc!=SQLITE_OK ) return rc;
      }

      assert( iNextStart<=iNextEnd );
      iStartChild = iNextStart;
      iEndChild = iNextEnd;
    }
    assert( iStartChild<=iLeavesEnd );
    assert( iEndChild<=iLeavesEnd );

    /* Scan through the leaf segments for doclists. */
    return loadSegmentLeaves(v, iStartChild, iEndChild,
                             pTerm, nTerm, isPrefix, out);
  }
}

/* Call loadSegmentInt() to collect the doclist for pTerm/nTerm, then
** merge its doclist over *out (any duplicate doclists read from the
** segment rooted at pData will overwrite those in *out).
*/
/* TODO(shess) Consider changing this to determine the depth of the
** leaves using either the first characters of interior nodes (when
** ==1, we're one level above the leaves), or the first character of
** the root (which will describe the height of the tree directly).
** Either feels somewhat tricky to me.
*/
/* TODO(shess) The current merge is likely to be slow for large
** doclists (though it should process from newest/smallest to
** oldest/largest, so it may not be that bad).  It might be useful to
** modify things to allow for N-way merging.  This could either be
** within a segment, with pairwise merges across segments, or across
** all segments at once.
*/
static int loadSegment(fulltext_vtab *v, const char *pData, int nData,
                       sqlite_int64 iLeavesEnd,
                       const char *pTerm, int nTerm, int isPrefix,
                       DataBuffer *out){
  DataBuffer result;
  int rc;

  assert( nData>1 );

  /* This code should never be called with buffered updates. */
  assert( v->nPendingData<0 );

  dataBufferInit(&result, 0);
  rc = loadSegmentInt(v, pData, nData, iLeavesEnd,
                      pTerm, nTerm, isPrefix, &result);
  if( rc==SQLITE_OK && result.nData>0 ){
    if( out->nData==0 ){
      DataBuffer tmp = *out;
      *out = result;
      result = tmp;
    }else{
      DataBuffer merged;
      DLReader readers[2];

      dlrInit(&readers[0], DL_DEFAULT, out->pData, out->nData);
      dlrInit(&readers[1], DL_DEFAULT, result.pData, result.nData);
      dataBufferInit(&merged, out->nData+result.nData);
      docListMerge(&merged, readers, 2);
      dataBufferDestroy(out);
      *out = merged;
      dlrDestroy(&readers[0]);
      dlrDestroy(&readers[1]);
    }
  }
  dataBufferDestroy(&result);
  return rc;
}

/* Scan the database and merge together the posting lists for the term
** into *out.
*/
static int termSelect(
  fulltext_vtab *v, 
  int iColumn,
  const char *pTerm, int nTerm,             /* Term to query for */
  int isPrefix,                             /* True for a prefix search */
  DocListType iType, 
  DataBuffer *out                           /* Write results here */
){
  DataBuffer doclist;
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  /* This code should never be called with buffered updates. */
  assert( v->nPendingData<0 );

  dataBufferInit(&doclist, 0);
  dataBufferInit(out, 0);

  /* Traverse the segments from oldest to newest so that newer doclist
  ** elements for given docids overwrite older elements.
  */
  while( (rc = sqlite3_step(s))==SQLITE_ROW ){
    const char *pData = sqlite3_column_blob(s, 2);
    const int nData = sqlite3_column_bytes(s, 2);
    const sqlite_int64 iLeavesEnd = sqlite3_column_int64(s, 1);
    rc = loadSegment(v, pData, nData, iLeavesEnd, pTerm, nTerm, isPrefix,
                     &doclist);
    if( rc!=SQLITE_OK ) goto err;
  }
  if( rc==SQLITE_DONE ){
    if( doclist.nData!=0 ){
      /* TODO(shess) The old term_select_all() code applied the column
      ** restrict as we merged segments, leading to smaller buffers.
      ** This is probably worthwhile to bring back, once the new storage
      ** system is checked in.
      */
      if( iColumn==v->nColumn) iColumn = -1;
      docListTrim(DL_DEFAULT, doclist.pData, doclist.nData,
                  iColumn, iType, out);
    }
    rc = SQLITE_OK;
  }

 err:
  dataBufferDestroy(&doclist);
  return rc;
}

/****************************************************************/
/* Used to hold hashtable data for sorting. */
typedef struct TermData {
  const char *pTerm;
  int nTerm;
  DLCollector *pCollector;
} TermData;

/* Orders TermData elements in strcmp fashion ( <0 for less-than, 0
** for equal, >0 for greater-than).
*/
static int termDataCmp(const void *av, const void *bv){
  const TermData *a = (const TermData *)av;
  const TermData *b = (const TermData *)bv;
  int n = a->nTerm<b->nTerm ? a->nTerm : b->nTerm;
  int c = memcmp(a->pTerm, b->pTerm, n);
  if( c!=0 ) return c;
  return a->nTerm-b->nTerm;
}

/* Order pTerms data by term, then write a new level 0 segment using
** LeafWriter.
*/
static int writeZeroSegment(fulltext_vtab *v, fts3Hash *pTerms){
  fts3HashElem *e;
  int idx, rc, i, n;
  TermData *pData;
  LeafWriter writer;
  DataBuffer dl;

  /* Determine the next index at level 0, merging as necessary. */
  rc = segdirNextIndex(v, 0, &idx);
  if( rc!=SQLITE_OK ) return rc;

  n = fts3HashCount(pTerms);
  pData = sqlite3_malloc(n*sizeof(TermData));

  for(i = 0, e = fts3HashFirst(pTerms); e; i++, e = fts3HashNext(e)){
    assert( i<n );
    pData[i].pTerm = fts3HashKey(e);
    pData[i].nTerm = fts3HashKeysize(e);
    pData[i].pCollector = fts3HashData(e);
  }
  assert( i==n );

  /* TODO(shess) Should we allow user-defined collation sequences,
  ** here?  I think we only need that once we support prefix searches.
  */
  if( n>1 ) qsort(pData, n, sizeof(*pData), termDataCmp);

  /* TODO(shess) Refactor so that we can write directly to the segment
  ** DataBuffer, as happens for segment merges.
  */
  leafWriterInit(0, idx, &writer);
  dataBufferInit(&dl, 0);
  for(i=0; i<n; i++){
    dataBufferReset(&dl);
    dlcAddDoclist(pData[i].pCollector, &dl);
    rc = leafWriterStep(v, &writer,
                        pData[i].pTerm, pData[i].nTerm, dl.pData, dl.nData);
    if( rc!=SQLITE_OK ) goto err;
  }
  rc = leafWriterFinalize(v, &writer);

 err:
  dataBufferDestroy(&dl);
  sqlite3_free(pData);
  leafWriterDestroy(&writer);
  return rc;
}

/* If pendingTerms has data, free it. */
static int clearPendingTerms(fulltext_vtab *v){
  if( v->nPendingData>=0 ){
    fts3HashElem *e;
    for(e=fts3HashFirst(&v->pendingTerms); e; e=fts3HashNext(e)){
      dlcDelete(fts3HashData(e));
    }
    fts3HashClear(&v->pendingTerms);
    v->nPendingData = -1;
  }
  return SQLITE_OK;
}

/* If pendingTerms has data, flush it to a level-zero segment, and
** free it.
*/
static int flushPendingTerms(fulltext_vtab *v){
  if( v->nPendingData>=0 ){
    int rc = writeZeroSegment(v, &v->pendingTerms);
    if( rc==SQLITE_OK ) clearPendingTerms(v);
    return rc;
  }
  return SQLITE_OK;
}

/* If pendingTerms is "too big", or docid is out of order, flush it.
** Regardless, be certain that pendingTerms is initialized for use.
*/
static int initPendingTerms(fulltext_vtab *v, sqlite_int64 iDocid){
  /* TODO(shess) Explore whether partially flushing the buffer on
  ** forced-flush would provide better performance.  I suspect that if
  ** we ordered the doclists by size and flushed the largest until the
  ** buffer was half empty, that would let the less frequent terms
  ** generate longer doclists.
  */
  if( iDocid<=v->iPrevDocid || v->nPendingData>kPendingThreshold ){
    int rc = flushPendingTerms(v);
    if( rc!=SQLITE_OK ) return rc;
  }
  if( v->nPendingData<0 ){
    fts3HashInit(&v->pendingTerms, FTS3_HASH_STRING, 1);
    v->nPendingData = 0;
  }
  v->iPrevDocid = iDocid;
  return SQLITE_OK;
}

/* This function implements the xUpdate callback; it is the top-level entry
 * point for inserting, deleting or updating a row in a full-text table. */
static int fulltextUpdate(sqlite3_vtab *pVtab, int nArg, sqlite3_value **ppArg,
                          sqlite_int64 *pRowid){
  fulltext_vtab *v = (fulltext_vtab *) pVtab;
  int rc;

  FTSTRACE(("FTS3 Update %p\n", pVtab));

  if( nArg<2 ){
    rc = index_delete(v, sqlite3_value_int64(ppArg[0]));
    if( rc==SQLITE_OK ){
      /* If we just deleted the last row in the table, clear out the
      ** index data.
      */
      rc = content_exists(v);
      if( rc==SQLITE_ROW ){
        rc = SQLITE_OK;
      }else if( rc==SQLITE_DONE ){
        /* Clear the pending terms so we don't flush a useless level-0
        ** segment when the transaction closes.
        */
        rc = clearPendingTerms(v);
        if( rc==SQLITE_OK ){
          rc = segdir_delete_all(v);
        }
      }
    }
  } else if( sqlite3_value_type(ppArg[0]) != SQLITE_NULL ){
    /* An update:
     * ppArg[0] = old rowid
     * ppArg[1] = new rowid
     * ppArg[2..2+v->nColumn-1] = values
     * ppArg[2+v->nColumn] = value for magic column (we ignore this)
     * ppArg[2+v->nColumn+1] = value for docid
     */
    sqlite_int64 rowid = sqlite3_value_int64(ppArg[0]);
    if( sqlite3_value_type(ppArg[1]) != SQLITE_INTEGER ||
        sqlite3_value_int64(ppArg[1]) != rowid ){
      rc = SQLITE_ERROR;  /* we don't allow changing the rowid */
    }else if( sqlite3_value_type(ppArg[2+v->nColumn+1]) != SQLITE_INTEGER ||
              sqlite3_value_int64(ppArg[2+v->nColumn+1]) != rowid ){
      rc = SQLITE_ERROR;  /* we don't allow changing the docid */
    }else{
      assert( nArg==2+v->nColumn+2);
      rc = index_update(v, rowid, &ppArg[2]);
    }
  } else {
    /* An insert:
     * ppArg[1] = requested rowid
     * ppArg[2..2+v->nColumn-1] = values
     * ppArg[2+v->nColumn] = value for magic column (we ignore this)
     * ppArg[2+v->nColumn+1] = value for docid
     */
    sqlite3_value *pRequestDocid = ppArg[2+v->nColumn+1];
    assert( nArg==2+v->nColumn+2);
    if( SQLITE_NULL != sqlite3_value_type(pRequestDocid) &&
        SQLITE_NULL != sqlite3_value_type(ppArg[1]) ){
      /* TODO(shess) Consider allowing this to work if the values are
      ** identical.  I'm inclined to discourage that usage, though,
      ** given that both rowid and docid are special columns.  Better
      ** would be to define one or the other as the default winner,
      ** but should it be fts3-centric (docid) or SQLite-centric
      ** (rowid)?
      */
      rc = SQLITE_ERROR;
    }else{
      if( SQLITE_NULL == sqlite3_value_type(pRequestDocid) ){
        pRequestDocid = ppArg[1];
      }
      rc = index_insert(v, pRequestDocid, &ppArg[2], pRowid);
    }
  }

  return rc;
}

static int fulltextSync(sqlite3_vtab *pVtab){
  FTSTRACE(("FTS3 xSync()\n"));
  return flushPendingTerms((fulltext_vtab *)pVtab);
}

static int fulltextBegin(sqlite3_vtab *pVtab){
  fulltext_vtab *v = (fulltext_vtab *) pVtab;
  FTSTRACE(("FTS3 xBegin()\n"));

  /* Any buffered updates should have been cleared by the previous
  ** transaction.
  */
  assert( v->nPendingData<0 );
  return clearPendingTerms(v);
}

static int fulltextCommit(sqlite3_vtab *pVtab){
  fulltext_vtab *v = (fulltext_vtab *) pVtab;
  FTSTRACE(("FTS3 xCommit()\n"));

  /* Buffered updates should have been cleared by fulltextSync(). */
  assert( v->nPendingData<0 );
  return clearPendingTerms(v);
}

static int fulltextRollback(sqlite3_vtab *pVtab){
  FTSTRACE(("FTS3 xRollback()\n"));
  return clearPendingTerms((fulltext_vtab *)pVtab);
}

/*
** Implementation of the snippet() function for FTS3
*/
static void snippetFunc(
  sqlite3_context *pContext,
  int argc,
  sqlite3_value **argv
){
  fulltext_cursor *pCursor;
  if( argc<1 ) return;
  if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
      sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
    sqlite3_result_error(pContext, "illegal first argument to html_snippet",-1);
  }else{
    const char *zStart = "<b>";
    const char *zEnd = "</b>";
    const char *zEllipsis = "<b>...</b>";
    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
    if( argc>=2 ){
      zStart = (const char*)sqlite3_value_text(argv[1]);
      if( argc>=3 ){
        zEnd = (const char*)sqlite3_value_text(argv[2]);
        if( argc>=4 ){
          zEllipsis = (const char*)sqlite3_value_text(argv[3]);
        }
      }
    }
    snippetAllOffsets(pCursor);
    snippetText(pCursor, zStart, zEnd, zEllipsis);
    sqlite3_result_text(pContext, pCursor->snippet.zSnippet,
                        pCursor->snippet.nSnippet, SQLITE_STATIC);
  }
}

/*
** Implementation of the offsets() function for FTS3
*/
static void snippetOffsetsFunc(
  sqlite3_context *pContext,
  int argc,
  sqlite3_value **argv
){
  fulltext_cursor *pCursor;
  if( argc<1 ) return;
  if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
      sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
    sqlite3_result_error(pContext, "illegal first argument to offsets",-1);
  }else{
    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
    snippetAllOffsets(pCursor);
    snippetOffsetText(&pCursor->snippet);
    sqlite3_result_text(pContext,
                        pCursor->snippet.zOffset, pCursor->snippet.nOffset,
                        SQLITE_STATIC);
  }

}

/* OptLeavesReader is nearly identical to LeavesReader, except that
** where LeavesReader is geared towards the merging of complete
** segment levels (with exactly MERGE_COUNT segments), OptLeavesReader
** is geared towards implementation of the optimize() function, and
** can merge all segments simultaneously.  This version may be
** somewhat less efficient than LeavesReader because it merges into an
** accumulator rather than doing an N-way merge, but since segment
** size grows exponentially (so segment count logrithmically) this is
** probably not an immediate problem.
*/
/* TODO(shess): Prove that assertion, or extend the merge code to
** merge tree fashion (like the prefix-searching code does).
*/
/* TODO(shess): OptLeavesReader and LeavesReader could probably be
** merged with little or no loss of performance for LeavesReader.  The
** merged code would need to handle >MERGE_COUNT segments, and would
** also need to be able to optionally optimize away deletes.
*/
typedef struct OptLeavesReader {
  /* Segment number, to order readers by age. */
  int segment;
  LeavesReader reader;
} OptLeavesReader;

static int optLeavesReaderAtEnd(OptLeavesReader *pReader){
  return leavesReaderAtEnd(&pReader->reader);
}
static int optLeavesReaderTermBytes(OptLeavesReader *pReader){
  return leavesReaderTermBytes(&pReader->reader);
}
static const char *optLeavesReaderData(OptLeavesReader *pReader){
  return leavesReaderData(&pReader->reader);
}
static int optLeavesReaderDataBytes(OptLeavesReader *pReader){
  return leavesReaderDataBytes(&pReader->reader);
}
static const char *optLeavesReaderTerm(OptLeavesReader *pReader){
  return leavesReaderTerm(&pReader->reader);
}
static int optLeavesReaderStep(fulltext_vtab *v, OptLeavesReader *pReader){
  return leavesReaderStep(v, &pReader->reader);
}
static int optLeavesReaderTermCmp(OptLeavesReader *lr1, OptLeavesReader *lr2){
  return leavesReaderTermCmp(&lr1->reader, &lr2->reader);
}
/* Order by term ascending, segment ascending (oldest to newest), with
** exhausted readers to the end.
*/
static int optLeavesReaderCmp(OptLeavesReader *lr1, OptLeavesReader *lr2){
  int c = optLeavesReaderTermCmp(lr1, lr2);
  if( c!=0 ) return c;
  return lr1->segment-lr2->segment;
}
/* Bubble pLr[0] to appropriate place in pLr[1..nLr-1].  Assumes that
** pLr[1..nLr-1] is already sorted.
*/
static void optLeavesReaderReorder(OptLeavesReader *pLr, int nLr){
  while( nLr>1 && optLeavesReaderCmp(pLr, pLr+1)>0 ){
    OptLeavesReader tmp = pLr[0];
    pLr[0] = pLr[1];
    pLr[1] = tmp;
    nLr--;
    pLr++;
  }
}

/* optimize() helper function.  Put the readers in order and iterate
** through them, merging doclists for matching terms into pWriter.
** Returns SQLITE_OK on success, or the SQLite error code which
** prevented success.
*/
static int optimizeInternal(fulltext_vtab *v,
                            OptLeavesReader *readers, int nReaders,
                            LeafWriter *pWriter){
  int i, rc = SQLITE_OK;
  DataBuffer doclist, merged, tmp;

  /* Order the readers. */
  i = nReaders;
  while( i-- > 0 ){
    optLeavesReaderReorder(&readers[i], nReaders-i);
  }

  dataBufferInit(&doclist, LEAF_MAX);
  dataBufferInit(&merged, LEAF_MAX);

  /* Exhausted readers bubble to the end, so when the first reader is
  ** at eof, all are at eof.
  */
  while( !optLeavesReaderAtEnd(&readers[0]) ){

    /* Figure out how many readers share the next term. */
    for(i=1; i<nReaders && !optLeavesReaderAtEnd(&readers[i]); i++){
      if( 0!=optLeavesReaderTermCmp(&readers[0], &readers[i]) ) break;
    }

    /* Special-case for no merge. */
    if( i==1 ){
      /* Trim deletions from the doclist. */
      dataBufferReset(&merged);
      docListTrim(DL_DEFAULT,
                  optLeavesReaderData(&readers[0]),
                  optLeavesReaderDataBytes(&readers[0]),
                  -1, DL_DEFAULT, &merged);
    }else{
      DLReader dlReaders[MERGE_COUNT];
      int iReader, nReaders;

      /* Prime the pipeline with the first reader's doclist.  After
      ** one pass index 0 will reference the accumulated doclist.
      */
      dlrInit(&dlReaders[0], DL_DEFAULT,
              optLeavesReaderData(&readers[0]),
              optLeavesReaderDataBytes(&readers[0]));
      iReader = 1;

      assert( iReader<i );  /* Must execute the loop at least once. */
      while( iReader<i ){
        /* Merge 16 inputs per pass. */
        for( nReaders=1; iReader<i && nReaders<MERGE_COUNT;
             iReader++, nReaders++ ){
          dlrInit(&dlReaders[nReaders], DL_DEFAULT,
                  optLeavesReaderData(&readers[iReader]),
                  optLeavesReaderDataBytes(&readers[iReader]));
        }

        /* Merge doclists and swap result into accumulator. */
        dataBufferReset(&merged);
        docListMerge(&merged, dlReaders, nReaders);
        tmp = merged;
        merged = doclist;
        doclist = tmp;

        while( nReaders-- > 0 ){
          dlrDestroy(&dlReaders[nReaders]);
        }

        /* Accumulated doclist to reader 0 for next pass. */
        dlrInit(&dlReaders[0], DL_DEFAULT, doclist.pData, doclist.nData);
      }

      /* Destroy reader that was left in the pipeline. */
      dlrDestroy(&dlReaders[0]);

      /* Trim deletions from the doclist. */
      dataBufferReset(&merged);
      docListTrim(DL_DEFAULT, doclist.pData, doclist.nData,
                  -1, DL_DEFAULT, &merged);
    }

    /* Only pass doclists with hits (skip if all hits deleted). */
    if( merged.nData>0 ){
      rc = leafWriterStep(v, pWriter,
                          optLeavesReaderTerm(&readers[0]),
                          optLeavesReaderTermBytes(&readers[0]),
                          merged.pData, merged.nData);
      if( rc!=SQLITE_OK ) goto err;
    }

    /* Step merged readers to next term and reorder. */
    while( i-- > 0 ){
      rc = optLeavesReaderStep(v, &readers[i]);
      if( rc!=SQLITE_OK ) goto err;

      optLeavesReaderReorder(&readers[i], nReaders-i);
    }
  }

 err:
  dataBufferDestroy(&doclist);
  dataBufferDestroy(&merged);
  return rc;
}

/* Implement optimize() function for FTS3.  optimize(t) merges all
** segments in the fts index into a single segment.  't' is the magic
** table-named column.
*/
static void optimizeFunc(sqlite3_context *pContext,
                         int argc, sqlite3_value **argv){
  fulltext_cursor *pCursor;
  if( argc>1 ){
    sqlite3_result_error(pContext, "excess arguments to optimize()",-1);
  }else if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
            sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
    sqlite3_result_error(pContext, "illegal first argument to optimize",-1);
  }else{
    fulltext_vtab *v;
    int i, rc, iMaxLevel;
    OptLeavesReader *readers;
    int nReaders;
    LeafWriter writer;
    sqlite3_stmt *s;

    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
    v = cursor_vtab(pCursor);

    /* Flush any buffered updates before optimizing. */
    rc = flushPendingTerms(v);
    if( rc!=SQLITE_OK ) goto err;

    rc = segdir_count(v, &nReaders, &iMaxLevel);
    if( rc!=SQLITE_OK ) goto err;
    if( nReaders==0 || nReaders==1 ){
      sqlite3_result_text(pContext, "Index already optimal", -1,
                          SQLITE_STATIC);
      return;
    }

    rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
    if( rc!=SQLITE_OK ) goto err;

    readers = sqlite3_malloc(nReaders*sizeof(readers[0]));
    if( readers==NULL ) goto err;

    /* Note that there will already be a segment at this position
    ** until we call segdir_delete() on iMaxLevel.
    */
    leafWriterInit(iMaxLevel, 0, &writer);

    i = 0;
    while( (rc = sqlite3_step(s))==SQLITE_ROW ){
      sqlite_int64 iStart = sqlite3_column_int64(s, 0);
      sqlite_int64 iEnd = sqlite3_column_int64(s, 1);
      const char *pRootData = sqlite3_column_blob(s, 2);
      int nRootData = sqlite3_column_bytes(s, 2);

      assert( i<nReaders );
      rc = leavesReaderInit(v, -1, iStart, iEnd, pRootData, nRootData,
                            &readers[i].reader);
      if( rc!=SQLITE_OK ) break;

      readers[i].segment = i;
      i++;
    }

    /* If we managed to successfully read them all, optimize them. */
    if( rc==SQLITE_DONE ){

      assert( i==nReaders );
      rc = optimizeInternal(v, readers, nReaders, &writer);

    }

    while( i-- > 0 ){
      leavesReaderDestroy(&readers[i].reader);
    }
    sqlite3_free(readers);

    /* If we've successfully gotten to here, delete the old segments
    ** and flush the interior structure of the new segment.
    */
    if( rc==SQLITE_OK ){
      for( i=0; i<=iMaxLevel; i++ ){
        rc = segdir_delete(v, i);
        if( rc!=SQLITE_OK ) break;
      }

      if( rc==SQLITE_OK ) rc = leafWriterFinalize(v, &writer);
    }

    leafWriterDestroy(&writer);

    if( rc!=SQLITE_OK ) goto err;

    sqlite3_result_text(pContext, "Index optimized", -1, SQLITE_STATIC);
    return;

    /* TODO(shess): Error-handling needs to be improved along the
    ** lines of the dump_ functions.



    */
 err:
    {
      char buf[512];
      sqlite3_snprintf(sizeof(buf), buf, "Error in optimize: %s",
                       sqlite3_errmsg(sqlite3_context_db_handle(pContext)));
      sqlite3_result_error(pContext, buf, -1);
    }
  }
}

#ifdef SQLITE_TEST
/* Generate an error of the form "<prefix>: <msg>".  If msg is NULL,
** pull the error from the context's db handle.

*/
static void generateError(sqlite3_context *pContext,
                          const char *prefix, const char *msg){
  char buf[512];
  if( msg==NULL ) msg = sqlite3_errmsg(sqlite3_context_db_handle(pContext));
  sqlite3_snprintf(sizeof(buf), buf, "%s: %s", prefix, msg);
  sqlite3_result_error(pContext, buf, -1);
}

/* Helper function to collect the set of terms in the segment into
** pTerms.  The segment is defined by the leaf nodes between
** iStartBlockid and iEndBlockid, inclusive, or by the contents of
** pRootData if iStartBlockid is 0 (in which case the entire segment
** fit in a leaf).

*/
static int collectSegmentTerms(fulltext_vtab *v, sqlite3_stmt *s,
                               fts3Hash *pTerms){
  const sqlite_int64 iStartBlockid = sqlite3_column_int64(s, 0);
  const sqlite_int64 iEndBlockid = sqlite3_column_int64(s, 1);
  const char *pRootData = sqlite3_column_blob(s, 2);
  const int nRootData = sqlite3_column_bytes(s, 2);
  LeavesReader reader;
  int rc = leavesReaderInit(v, 0, iStartBlockid, iEndBlockid,
                            pRootData, nRootData, &reader);
  if( rc!=SQLITE_OK ) return rc;

  while( rc==SQLITE_OK && !leavesReaderAtEnd(&reader) ){
    const char *pTerm = leavesReaderTerm(&reader);
    const int nTerm = leavesReaderTermBytes(&reader);
    void *oldValue = sqlite3Fts3HashFind(pTerms, pTerm, nTerm);
    void *newValue = (void *)((char *)oldValue+1);

    /* From the comment before sqlite3Fts3HashInsert in fts3_hash.c,
    ** the data value passed is returned in case of malloc failure.
    */
    if( newValue==sqlite3Fts3HashInsert(pTerms, pTerm, nTerm, newValue) ){
      rc = SQLITE_NOMEM;
    }else{
      rc = leavesReaderStep(v, &reader);
    }
  }

  leavesReaderDestroy(&reader);
  return rc;
}

/* Helper function to build the result string for dump_terms(). */
static int generateTermsResult(sqlite3_context *pContext, fts3Hash *pTerms){
  int iTerm, nTerms, nResultBytes, iByte;
  char *result;
  TermData *pData;
  fts3HashElem *e;

  /* Iterate pTerms to generate an array of terms in pData for
  ** sorting.
  */
  nTerms = fts3HashCount(pTerms);
  assert( nTerms>0 );
  pData = sqlite3_malloc(nTerms*sizeof(TermData));
  if( pData==NULL ) return SQLITE_NOMEM;

  nResultBytes = 0;
  for(iTerm = 0, e = fts3HashFirst(pTerms); e; iTerm++, e = fts3HashNext(e)){
    nResultBytes += fts3HashKeysize(e)+1;   /* Term plus trailing space */
    assert( iTerm<nTerms );
    pData[iTerm].pTerm = fts3HashKey(e);
    pData[iTerm].nTerm = fts3HashKeysize(e);
    pData[iTerm].pCollector = fts3HashData(e);  /* unused */
  }
  assert( iTerm==nTerms );

  assert( nResultBytes>0 );   /* nTerms>0, nResultsBytes must be, too. */
  result = sqlite3_malloc(nResultBytes);
  if( result==NULL ){
    sqlite3_free(pData);
    return SQLITE_NOMEM;
  }

  if( nTerms>1 ) qsort(pData, nTerms, sizeof(*pData), termDataCmp);

  /* Read the terms in order to build the result. */
  iByte = 0;
  for(iTerm=0; iTerm<nTerms; ++iTerm){
    memcpy(result+iByte, pData[iTerm].pTerm, pData[iTerm].nTerm);
    iByte += pData[iTerm].nTerm;
    result[iByte++] = ' ';
  }
  assert( iByte==nResultBytes );
  assert( result[nResultBytes-1]==' ' );
  result[nResultBytes-1] = '\0';

  /* Passes away ownership of result. */
  sqlite3_result_text(pContext, result, nResultBytes-1, sqlite3_free);
  sqlite3_free(pData);
  return SQLITE_OK;
}

/* Implements dump_terms() for use in inspecting the fts3 index from
** tests.  TEXT result containing the ordered list of terms joined by
** spaces.  dump_terms(t, level, idx) dumps the terms for the segment
** specified by level, idx (in %_segdir), while dump_terms(t) dumps
** all terms in the index.  In both cases t is the fts table's magic
** table-named column.
*/
static void dumpTermsFunc(
  sqlite3_context *pContext,

  int argc, sqlite3_value **argv
){
  fulltext_cursor *pCursor;
  if( argc!=3 && argc!=1 ){
    generateError(pContext, "dump_terms", "incorrect arguments");
  }else if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
            sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
    generateError(pContext, "dump_terms", "illegal first argument");
  }else{
    fulltext_vtab *v;
    fts3Hash terms;
    sqlite3_stmt *s = NULL;
    int rc;

    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
    v = cursor_vtab(pCursor);

    /* If passed only the cursor column, get all segments.  Otherwise
    ** get the segment described by the following two arguments.
    */
    if( argc==1 ){
      rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
    }else{
      rc = sql_get_statement(v, SEGDIR_SELECT_SEGMENT_STMT, &s);
      if( rc==SQLITE_OK ){
        rc = sqlite3_bind_int(s, 1, sqlite3_value_int(argv[1]));
        if( rc==SQLITE_OK ){
          rc = sqlite3_bind_int(s, 2, sqlite3_value_int(argv[2]));
        }
      }
    }

    if( rc!=SQLITE_OK ){
      generateError(pContext, "dump_terms", NULL);
      return;
    }

    /* Collect the terms for each segment. */
    sqlite3Fts3HashInit(&terms, FTS3_HASH_STRING, 1);
    while( (rc = sqlite3_step(s))==SQLITE_ROW ){
      rc = collectSegmentTerms(v, s, &terms);
      if( rc!=SQLITE_OK ) break;
    }

    if( rc!=SQLITE_DONE ){
      sqlite3_reset(s);
      generateError(pContext, "dump_terms", NULL);
    }else{
      const int nTerms = fts3HashCount(&terms);
      if( nTerms>0 ){
        rc = generateTermsResult(pContext, &terms);
        if( rc==SQLITE_NOMEM ){
          generateError(pContext, "dump_terms", "out of memory");
        }else{
          assert( rc==SQLITE_OK );
        }
      }else if( argc==3 ){
        /* The specific segment asked for could not be found. */
        generateError(pContext, "dump_terms", "segment not found");
      }else{
        /* No segments found. */
        /* TODO(shess): It should be impossible to reach this.  This
        ** case can only happen for an empty table, in which case
        ** SQLite has no rows to call this function on.
        */
        sqlite3_result_null(pContext);
      }
    }
    sqlite3Fts3HashClear(&terms);
  }
}

/* Expand the DL_DEFAULT doclist in pData into a text result in
** pContext.
*/
static void createDoclistResult(sqlite3_context *pContext,
                                const char *pData, int nData){
  DataBuffer dump;
  DLReader dlReader;

  assert( pData!=NULL && nData>0 );

  dataBufferInit(&dump, 0);
  dlrInit(&dlReader, DL_DEFAULT, pData, nData);
  for( ; !dlrAtEnd(&dlReader); dlrStep(&dlReader) ){
    char buf[256];
    PLReader plReader;

    plrInit(&plReader, &dlReader);
    if( DL_DEFAULT==DL_DOCIDS || plrAtEnd(&plReader) ){
      sqlite3_snprintf(sizeof(buf), buf, "[%lld] ", dlrDocid(&dlReader));
      dataBufferAppend(&dump, buf, strlen(buf));
    }else{
      int iColumn = plrColumn(&plReader);

      sqlite3_snprintf(sizeof(buf), buf, "[%lld %d[",
                       dlrDocid(&dlReader), iColumn);
      dataBufferAppend(&dump, buf, strlen(buf));

      for( ; !plrAtEnd(&plReader); plrStep(&plReader) ){
        if( plrColumn(&plReader)!=iColumn ){
          iColumn = plrColumn(&plReader);
          sqlite3_snprintf(sizeof(buf), buf, "] %d[", iColumn);
          assert( dump.nData>0 );
          dump.nData--;                     /* Overwrite trailing space. */
          assert( dump.pData[dump.nData]==' ');
          dataBufferAppend(&dump, buf, strlen(buf));


        }
        if( DL_DEFAULT==DL_POSITIONS_OFFSETS ){
          sqlite3_snprintf(sizeof(buf), buf, "%d,%d,%d ",
                           plrPosition(&plReader),
                           plrStartOffset(&plReader), plrEndOffset(&plReader));
        }else if( DL_DEFAULT==DL_POSITIONS ){
          sqlite3_snprintf(sizeof(buf), buf, "%d ", plrPosition(&plReader));
        }else{
          assert( NULL=="Unhandled DL_DEFAULT value");

        }
        dataBufferAppend(&dump, buf, strlen(buf));
      }
      plrDestroy(&plReader);

      assert( dump.nData>0 );
      dump.nData--;                     /* Overwrite trailing space. */
      assert( dump.pData[dump.nData]==' ');
      dataBufferAppend(&dump, "]] ", 3);
    }
  }
  dlrDestroy(&dlReader);



  assert( dump.nData>0 );
  dump.nData--;                     /* Overwrite trailing space. */
  assert( dump.pData[dump.nData]==' ');
  dump.pData[dump.nData] = '\0';
  assert( dump.nData>0 );

  /* Passes ownership of dump's buffer to pContext. */
  sqlite3_result_text(pContext, dump.pData, dump.nData, sqlite3_free);
  dump.pData = NULL;
  dump.nData = dump.nCapacity = 0;
}

/* Implements dump_doclist() for use in inspecting the fts3 index from
** tests.  TEXT result containing a string representation of the
** doclist for the indicated term.  dump_doclist(t, term, level, idx)
** dumps the doclist for term from the segment specified by level, idx
** (in %_segdir), while dump_doclist(t, term) dumps the logical
** doclist for the term across all segments.  The per-segment doclist
** can contain deletions, while the full-index doclist will not
** (deletions are omitted).
**
** Result formats differ with the setting of DL_DEFAULTS.  Examples:
**
** DL_DOCIDS: [1] [3] [7]
** DL_POSITIONS: [1 0[0 4] 1[17]] [3 1[5]]
** DL_POSITIONS_OFFSETS: [1 0[0,0,3 4,23,26] 1[17,102,105]] [3 1[5,20,23]]
**
** In each case the number after the outer '[' is the docid.  In the
** latter two cases, the number before the inner '[' is the column
** associated with the values within.  For DL_POSITIONS the numbers
** within are the positions, for DL_POSITIONS_OFFSETS they are the
** position, the start offset, and the end offset.
*/
static void dumpDoclistFunc(
  sqlite3_context *pContext,
  int argc, sqlite3_value **argv
){
  fulltext_cursor *pCursor;
  if( argc!=2 && argc!=4 ){
    generateError(pContext, "dump_doclist", "incorrect arguments");
  }else if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
            sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
    generateError(pContext, "dump_doclist", "illegal first argument");
  }else if( sqlite3_value_text(argv[1])==NULL ||
            sqlite3_value_text(argv[1])[0]=='\0' ){
    generateError(pContext, "dump_doclist", "empty second argument");
  }else{
    const char *pTerm = (const char *)sqlite3_value_text(argv[1]);
    const int nTerm = strlen(pTerm);
    fulltext_vtab *v;
    int rc;
    DataBuffer doclist;

    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
    v = cursor_vtab(pCursor);

    dataBufferInit(&doclist, 0);

    /* termSelect() yields the same logical doclist that queries are
    ** run against.
    */
    if( argc==2 ){
      rc = termSelect(v, v->nColumn, pTerm, nTerm, 0, DL_DEFAULT, &doclist);
    }else{
      sqlite3_stmt *s = NULL;

      /* Get our specific segment's information. */
      rc = sql_get_statement(v, SEGDIR_SELECT_SEGMENT_STMT, &s);
      if( rc==SQLITE_OK ){
        rc = sqlite3_bind_int(s, 1, sqlite3_value_int(argv[2]));
        if( rc==SQLITE_OK ){
          rc = sqlite3_bind_int(s, 2, sqlite3_value_int(argv[3]));
        }
      }

      if( rc==SQLITE_OK ){
        rc = sqlite3_step(s);

        if( rc==SQLITE_DONE ){
          dataBufferDestroy(&doclist);
          generateError(pContext, "dump_doclist", "segment not found");
          return;
        }

        /* Found a segment, load it into doclist. */
        if( rc==SQLITE_ROW ){
          const sqlite_int64 iLeavesEnd = sqlite3_column_int64(s, 1);
          const char *pData = sqlite3_column_blob(s, 2);
          const int nData = sqlite3_column_bytes(s, 2);

          /* loadSegment() is used by termSelect() to load each
          ** segment's data.
          */
          rc = loadSegment(v, pData, nData, iLeavesEnd, pTerm, nTerm, 0,
                           &doclist);

          if( rc==SQLITE_OK ){
            rc = sqlite3_step(s);

            /* Should not have more than one matching segment. */


            if( rc!=SQLITE_DONE ){
              sqlite3_reset(s);
              dataBufferDestroy(&doclist);
              generateError(pContext, "dump_doclist", "invalid segdir");
              return;
            }
            rc = SQLITE_OK;
          }
        }
      }

      sqlite3_reset(s);
    }

    if( rc==SQLITE_OK ){
      if( doclist.nData>0 ){
        createDoclistResult(pContext, doclist.pData, doclist.nData);
      }else{
        /* TODO(shess): This can happen if the term is not present, or
        ** if all instances of the term have been deleted and this is
        ** an all-index dump.  It may be interesting to distinguish
        ** these cases.
        */
        sqlite3_result_text(pContext, "", 0, SQLITE_STATIC);




      }
    }else if( rc==SQLITE_NOMEM ){
      /* Handle out-of-memory cases specially because if they are
      ** generated in fts3 code they may not be reflected in the db
      ** handle.
      */
      /* TODO(shess): Handle this more comprehensively.
      ** sqlite3ErrStr() has what I need, but is internal.
      */
      generateError(pContext, "dump_doclist", "out of memory");
    }else{
      generateError(pContext, "dump_doclist", NULL);
    }

    dataBufferDestroy(&doclist);
  }
}
#endif

/*
** This routine implements the xFindFunction method for the FTS3
** virtual table.
*/
static int fulltextFindFunction(
  sqlite3_vtab *pVtab,
  int nArg,

  const char *zName,
  void (**pxFunc)(sqlite3_context*,int,sqlite3_value**),
  void **ppArg
){
  if( strcmp(zName,"snippet")==0 ){
    *pxFunc = snippetFunc;
    return 1;
  }else if( strcmp(zName,"offsets")==0 ){





    *pxFunc = snippetOffsetsFunc;
    return 1;









  }else if( strcmp(zName,"optimize")==0 ){
    *pxFunc = optimizeFunc;
    return 1;
#ifdef SQLITE_TEST
    /* NOTE(shess): These functions are present only for testing
    ** purposes.  No particular effort is made to optimize their
    ** execution or how they build their results.
    */
  }else if( strcmp(zName,"dump_terms")==0 ){
    /* fprintf(stderr, "Found dump_terms\n"); */
    *pxFunc = dumpTermsFunc;
    return 1;
  }else if( strcmp(zName,"dump_doclist")==0 ){
    /* fprintf(stderr, "Found dump_doclist\n"); */
    *pxFunc = dumpDoclistFunc;
    return 1;
#endif
  }



  return 0;
}

/*
** Rename an fts3 table.
*/
static int fulltextRename(
  sqlite3_vtab *pVtab,
  const char *zName
){
  fulltext_vtab *p = (fulltext_vtab *)pVtab;
  int rc = SQLITE_NOMEM;


  char *zSql = sqlite3_mprintf(
    "ALTER TABLE %Q.'%q_content'  RENAME TO '%q_content';"
    "ALTER TABLE %Q.'%q_segments' RENAME TO '%q_segments';"
    "ALTER TABLE %Q.'%q_segdir'   RENAME TO '%q_segdir';"
    , p->zDb, p->zName, zName 
    , p->zDb, p->zName, zName 
    , p->zDb, p->zName, zName
  );
................................................................................
    sqlite3_free(zSql);
  }
  return rc;
}

static const sqlite3_module fts3Module = {
  /* iVersion      */ 0,
  /* xCreate       */ fulltextCreate,
  /* xConnect      */ fulltextConnect,
  /* xBestIndex    */ fulltextBestIndex,
  /* xDisconnect   */ fulltextDisconnect,
  /* xDestroy      */ fulltextDestroy,
  /* xOpen         */ fulltextOpen,
  /* xClose        */ fulltextClose,
  /* xFilter       */ fulltextFilter,
  /* xNext         */ fulltextNext,
  /* xEof          */ fulltextEof,
  /* xColumn       */ fulltextColumn,
  /* xRowid        */ fulltextRowid,
  /* xUpdate       */ fulltextUpdate,
  /* xBegin        */ fulltextBegin,
  /* xSync         */ fulltextSync,
  /* xCommit       */ fulltextCommit,
  /* xRollback     */ fulltextRollback,
  /* xFindFunction */ fulltextFindFunction,
  /* xRename */       fulltextRename,
};






static void hashDestroy(void *p){
  fts3Hash *pHash = (fts3Hash *)p;
  sqlite3Fts3HashClear(pHash);
  sqlite3_free(pHash);
}

/*
** The fts3 built-in tokenizers - "simple" and "porter" - are implemented
** in files fts3_tokenizer1.c and fts3_porter.c respectively. The following
................................................................................
** Function ...PorterTokenizerModule() sets *pModule to point to the
** porter tokenizer/stemmer implementation.
*/
void sqlite3Fts3SimpleTokenizerModule(sqlite3_tokenizer_module const**ppModule);
void sqlite3Fts3PorterTokenizerModule(sqlite3_tokenizer_module const**ppModule);
void sqlite3Fts3IcuTokenizerModule(sqlite3_tokenizer_module const**ppModule);

int sqlite3Fts3InitHashTable(sqlite3 *, fts3Hash *, const char *);

/*
** Initialise the fts3 extension. If this extension is built as part
** of the sqlite library, then this function is called directly by
** SQLite. If fts3 is built as a dynamically loadable extension, this
** function is called by the sqlite3_extension_init() entry point.
*/
int sqlite3Fts3Init(sqlite3 *db){
  int rc = SQLITE_OK;
  fts3Hash *pHash = 0;
  const sqlite3_tokenizer_module *pSimple = 0;
  const sqlite3_tokenizer_module *pPorter = 0;
  const sqlite3_tokenizer_module *pIcu = 0;

  sqlite3Fts3SimpleTokenizerModule(&pSimple);
  sqlite3Fts3PorterTokenizerModule(&pPorter);
#ifdef SQLITE_ENABLE_ICU
  sqlite3Fts3IcuTokenizerModule(&pIcu);
#endif

  /* Allocate and initialise the hash-table used to store tokenizers. */
  pHash = sqlite3_malloc(sizeof(fts3Hash));
  if( !pHash ){
    rc = SQLITE_NOMEM;
  }else{
    sqlite3Fts3HashInit(pHash, FTS3_HASH_STRING, 1);
  }

  /* Load the built-in tokenizers into the hash table */
................................................................................
  /* Create the virtual table wrapper around the hash-table and overload 
  ** the two scalar functions. If this is successful, register the
  ** module with sqlite.
  */
  if( SQLITE_OK==rc 
   && SQLITE_OK==(rc = sqlite3Fts3InitHashTable(db, pHash, "fts3_tokenizer"))
   && SQLITE_OK==(rc = sqlite3_overload_function(db, "snippet", -1))
   && SQLITE_OK==(rc = sqlite3_overload_function(db, "offsets", -1))
   && SQLITE_OK==(rc = sqlite3_overload_function(db, "optimize", -1))
#ifdef SQLITE_TEST
   && SQLITE_OK==(rc = sqlite3_overload_function(db, "dump_terms", -1))
   && SQLITE_OK==(rc = sqlite3_overload_function(db, "dump_doclist", -1))
#endif
  ){
    return sqlite3_create_module_v2(
        db, "fts3", &fts3Module, (void *)pHash, hashDestroy
    );
  }

  /* An error has occurred. Delete the hash table and return the error code. */
................................................................................
  const sqlite3_api_routines *pApi
){
  SQLITE_EXTENSION_INIT2(pApi)
  return sqlite3Fts3Init(db);
}
#endif

#endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3) */

#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3)

#if defined(SQLITE_ENABLE_FTS3) && !defined(SQLITE_CORE)
# define SQLITE_CORE 1
#endif

#include "fts3Int.h"

#include <assert.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>


#include "fts3.h"



#ifndef SQLITE_CORE 
# include "sqlite3ext.h"
  SQLITE_EXTENSION_INIT1
#endif



/* TODO(shess) MAN, this thing needs some refactoring.  At minimum, it
** would be nice to order the file better, perhaps something along the
** lines of:
**
**  - utility functions
................................................................................

#if 0
# define FTSTRACE(A)  printf A; fflush(stdout)
#else
# define FTSTRACE(A)
#endif




















typedef enum DocListType {
  DL_DOCIDS,              /* docids only */
  DL_POSITIONS,           /* docids + positions */
  DL_POSITIONS_OFFSETS    /* docids + positions + offsets */
} DocListType;

/*
................................................................................

enum {
  POS_END = 0,        /* end of this position list */
  POS_COLUMN,         /* followed by new column number */
  POS_BASE
};






/* utility functions */

/* CLEAR() and SCRAMBLE() abstract memset() on a pointer to a single
** record to prevent errors of the form:
**
** my_function(SomeType *b){
**   memset(b, '\0', sizeof(b));  // sizeof(b)!=sizeof(*b)
................................................................................

#ifndef NDEBUG
#  define SCRAMBLE(b) memset(b, 0x55, sizeof(*(b)))
#else
#  define SCRAMBLE(b)
#endif

/* 


** Write a 64-bit variable-length integer to memory starting at p[0].
** The length of data written will be between 1 and FTS3_VARINT_MAX bytes.
** The number of bytes written is returned.
*/
int sqlite3Fts3PutVarint(char *p, sqlite_int64 v){
  unsigned char *q = (unsigned char *) p;
  sqlite_uint64 vu = v;
  do{
    *q++ = (unsigned char) ((vu & 0x7f) | 0x80);
    vu >>= 7;
  }while( vu!=0 );
  q[-1] &= 0x7f;  /* turn off high bit in final byte */
  assert( q - (unsigned char *)p <= FTS3_VARINT_MAX );
  return (int) (q - (unsigned char *)p);
}

/* 
** Read a 64-bit variable-length integer from memory starting at p[0].
** Return the number of bytes read, or 0 on error.
** The value is stored in *v.
*/
int sqlite3Fts3GetVarint(const char *p, sqlite_int64 *v){
  const unsigned char *q = (const unsigned char *) p;
  sqlite_uint64 x = 0, y = 1;
  while( (*q & 0x80) == 0x80 ){
    x += y * (*q++ & 0x7f);
    y <<= 7;
    if( q - (unsigned char *)p >= FTS3_VARINT_MAX ){  /* bad data */
      assert( 0 );
      return 0;
    }
  }
  x += y * (*q++);
  *v = (sqlite_int64) x;
  return (int) (q - (unsigned char *)p);
}

/*
** Similar to sqlite3Fts3GetVarint(), except that the output is truncated to a
** 32-bit integer before it is returned.
*/
int sqlite3Fts3GetVarint32(const char *p, int *pi){
 sqlite_int64 i;
 int ret = sqlite3Fts3GetVarint(p, &i);
 *pi = (int) i;
 assert( *pi==i );
 return ret;
}





















































































































































































































































































































































































































































































































































































































































































































































































































































































































































































/*



















** Return the number of bytes required to store the value passed as the
** first argument in varint form.
*/














































































































































































































































































































































































































































































































































































int sqlite3Fts3VarintLen(sqlite3_uint64 v){
  int i = 0;

















































































































































































































































































































































































































































































































































































  do{
    i++;
























































    v >>= 7;
  }while( v!=0 );






















  return i;
}

/*
** Convert an SQL-style quoted string into a normal string by removing
** the quote characters.  The conversion is done in-place.  If the
** input does not begin with a quote character, then this routine
** is a no-op.
................................................................................
** Examples:
**
**     "abc"   becomes   abc
**     'xyz'   becomes   xyz
**     [pqr]   becomes   pqr
**     `mno`   becomes   mno
*/
void sqlite3Fts3Dequote(char *z){
  int quote;
  int i, j;


  quote = z[0];
  switch( quote ){
    case '\'':  break;
    case '"':   break;
    case '`':   break;                /* For MySQL compatibility */
    case '[':   quote = ']';  break;  /* For MS SqlServer compatibility */
    default:    return;
  }
  for(i=1, j=0; z[i]; i++){
    if( z[i]==quote ){
      if( z[i+1]==quote ){
        z[j++] = (char)quote;
        i++;
      }else{
        z[j++] = 0;
        break;
      }
    }else{
      z[j++] = z[i];
    }
  }
}

static void fts3GetDeltaVarint(char **pp, sqlite3_int64 *pVal){
  sqlite3_int64 iVal;
  *pp += sqlite3Fts3GetVarint(*pp, &iVal);
  *pVal += iVal;
}

static void fts3GetDeltaVarint2(char **pp, char *pEnd, sqlite3_int64 *pVal){
  if( *pp>=pEnd ){
    *pp = 0;
  }else{
    fts3GetDeltaVarint(pp, pVal);
  }
}

/*
** The xDisconnect() virtual table method.
*/
static int fts3DisconnectMethod(sqlite3_vtab *pVtab){
  Fts3Table *p = (Fts3Table *)pVtab;
  int i;

  assert( p->nPendingData==0 );

  /* Free any prepared statements held */
  for(i=0; i<SizeofArray(p->aStmt); i++){
    sqlite3_finalize(p->aStmt[i]);
  }
  for(i=0; i<p->nLeavesStmt; i++){
    sqlite3_finalize(p->aLeavesStmt[i]);
  }
  sqlite3_free(p->zSelectLeaves);
  sqlite3_free(p->aLeavesStmt);

  /* Invoke the tokenizer destructor to free the tokenizer. */
  p->pTokenizer->pModule->xDestroy(p->pTokenizer);

  sqlite3_free(p);
  return SQLITE_OK;
}

/*
** The xDestroy() virtual table method.
*/
static int fts3DestroyMethod(sqlite3_vtab *pVtab){
  int rc;                         /* Return code */
  Fts3Table *p = (Fts3Table *)pVtab;

  /* Create a script to drop the underlying three storage tables. */
  char *zSql = sqlite3_mprintf(
      "DROP TABLE IF EXISTS %Q.'%q_content';"
      "DROP TABLE IF EXISTS %Q.'%q_segments';"
      "DROP TABLE IF EXISTS %Q.'%q_segdir';", 
      p->zDb, p->zName, p->zDb, p->zName, p->zDb, p->zName
  );

  /* If malloc has failed, set rc to SQLITE_NOMEM. Otherwise, try to
  ** execute the SQL script created above.
  */
  if( zSql ){
    rc = sqlite3_exec(p->db, zSql, 0, 0, 0);
    sqlite3_free(zSql);
  }else{
    rc = SQLITE_NOMEM;
  }

  /* If everything has worked, invoke fts3DisconnectMethod() to free the
  ** memory associated with the Fts3Table structure and return SQLITE_OK.
  ** Otherwise, return an SQLite error code.
  */
  return (rc==SQLITE_OK ? fts3DisconnectMethod(pVtab) : rc);
}


/*
** Invoke sqlite3_declare_vtab() to declare the schema for the FTS3 table
** passed as the first argument. This is done as part of the xConnect()
** and xCreate() methods.
*/
static int fts3DeclareVtab(Fts3Table *p){
  int i;                          /* Iterator variable */
  int rc;                         /* Return code */
  char *zSql;                     /* SQL statement passed to declare_vtab() */
  char *zCols;                    /* List of user defined columns */

  /* Create a list of user columns for the virtual table */
  zCols = sqlite3_mprintf("%Q, ", p->azColumn[0]);
  for(i=1; zCols && i<p->nColumn; i++){
    zCols = sqlite3_mprintf("%z%Q, ", zCols, p->azColumn[i]);
  }

  /* Create the whole "CREATE TABLE" statement to pass to SQLite */
  zSql = sqlite3_mprintf(
      "CREATE TABLE x(%s %Q HIDDEN, docid HIDDEN)", zCols, p->zName
  );

  if( !zCols || !zSql ){
    rc = SQLITE_NOMEM;
  }else{
    rc = sqlite3_declare_vtab(p->db, zSql);
  }

  sqlite3_free(zSql);
  sqlite3_free(zCols);
  return rc;
}

/*
** Create the backing store tables (%_content, %_segments and %_segdir)
** required by the FTS3 table passed as the only argument. This is done
** as part of the vtab xCreate() method.
*/
static int fts3CreateTables(Fts3Table *p){
  int rc;                         /* Return code */
  int i;                          /* Iterator variable */
  char *zContentCols;             /* Columns of %_content table */
  char *zSql;                     /* SQL script to create required tables */

  /* Create a list of user columns for the content table */
  zContentCols = sqlite3_mprintf("docid INTEGER PRIMARY KEY");
  for(i=0; zContentCols && i<p->nColumn; i++){
    char *z = p->azColumn[i];
    zContentCols = sqlite3_mprintf("%z, 'c%d%q'", zContentCols, i, z);
  }

  /* Create the whole SQL script */
  zSql = sqlite3_mprintf(
      "CREATE TABLE %Q.'%q_content'(%s);"
      "CREATE TABLE %Q.'%q_segments'(blockid INTEGER PRIMARY KEY, block BLOB);"
      "CREATE TABLE %Q.'%q_segdir'("
        "level INTEGER,"
        "idx INTEGER,"
        "start_block INTEGER,"
        "leaves_end_block INTEGER,"
        "end_block INTEGER,"
        "root BLOB,"
        "PRIMARY KEY(level, idx)"
      ");",
      p->zDb, p->zName, zContentCols, p->zDb, p->zName, p->zDb, p->zName
  );

  /* Unless a malloc() failure has occurred, execute the SQL script to 
  ** create the tables used to store data for this FTS3 virtual table.
  */
  if( zContentCols==0 || zSql==0 ){
    rc = SQLITE_NOMEM;
  }else{
    rc = sqlite3_exec(p->db, zSql, 0, 0, 0);
  }

  sqlite3_free(zSql);
  sqlite3_free(zContentCols);
  return rc;
}

/*
** This function is the implementation of both the xConnect and xCreate
** methods of the FTS3 virtual table.
**
** The argv[] array contains the following:
**
**   argv[0]   -> module name
**   argv[1]   -> database name
**   argv[2]   -> table name
**   argv[...] -> "column name" and other module argument fields.
*/
int fts3InitVtab(
  int isCreate,                   /* True for xCreate, false for xConnect */
  sqlite3 *db,                    /* The SQLite database connection */
  void *pAux,                     /* Hash table containing tokenizers */
  int argc,                       /* Number of elements in argv array */
  const char * const *argv,       /* xCreate/xConnect argument array */
  sqlite3_vtab **ppVTab,          /* Write the resulting vtab structure here */
  char **pzErr                    /* Write any error message here */
){
  Fts3Hash *pHash = (Fts3Hash *)pAux;
  Fts3Table *p;                   /* Pointer to allocated vtab */
  int rc;                         /* Return code */
  int i;                          /* Iterator variable */
  int nByte;                      /* Size of allocation used for *p */
  int iCol;
  int nString = 0;
  int nCol = 0;
  char *zCsr;
  int nDb;
  int nName;

  const char *zTokenizer = 0;               /* Name of tokenizer to use */
  sqlite3_tokenizer *pTokenizer = 0;        /* Tokenizer for this table */

#ifdef SQLITE_TEST
  const char *zTestParam = 0;
  if( strncmp(argv[argc-1], "test:", 5)==0 ){
    zTestParam = argv[argc-1];
    argc--;
  }
#endif

  nDb = (int)strlen(argv[1]) + 1;
  nName = (int)strlen(argv[2]) + 1;
  for(i=3; i<argc; i++){
    char const *z = argv[i];
    rc = sqlite3Fts3InitTokenizer(pHash, z, &pTokenizer, &zTokenizer, pzErr);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    if( z!=zTokenizer ){
      nString += (int)(strlen(z) + 1);
    }
  }
  nCol = argc - 3 - (zTokenizer!=0);
  if( zTokenizer==0 ){
    rc = sqlite3Fts3InitTokenizer(pHash, 0, &pTokenizer, 0, pzErr);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    assert( pTokenizer );
  }

  if( nCol==0 ){
    nCol = 1;
  }

  /* Allocate and populate the Fts3Table structure. */
  nByte = sizeof(Fts3Table) +              /* Fts3Table */
          nCol * sizeof(char *) +              /* azColumn */
          nName +                              /* zName */
          nDb +                                /* zDb */
          nString;                             /* Space for azColumn strings */
  p = (Fts3Table*)sqlite3_malloc(nByte);
  if( p==0 ){
    rc = SQLITE_NOMEM;
    goto fts3_init_out;
  }
  memset(p, 0, nByte);

  p->db = db;
  p->nColumn = nCol;
  p->nPendingData = 0;
  p->azColumn = (char **)&p[1];
  p->pTokenizer = pTokenizer;
  p->nNodeSize = 1000;
  zCsr = (char *)&p->azColumn[nCol];

  fts3HashInit(&p->pendingTerms, FTS3_HASH_STRING, 1);

  /* Fill in the zName and zDb fields of the vtab structure. */
  p->zName = zCsr;
  memcpy(zCsr, argv[2], nName);
  zCsr += nName;
  p->zDb = zCsr;
  memcpy(zCsr, argv[1], nDb);
  zCsr += nDb;

  /* Fill in the azColumn array */
  iCol = 0;
  for(i=3; i<argc; i++){
    if( argv[i]!=zTokenizer ){
      char *z; 
      int n;
      z = (char *)sqlite3Fts3NextToken(argv[i], &n);
      memcpy(zCsr, z, n);
      zCsr[n] = '\0';
      sqlite3Fts3Dequote(zCsr);
      p->azColumn[iCol++] = zCsr;
      zCsr += n+1;
      assert( zCsr <= &((char *)p)[nByte] );
    }
  }
  if( iCol==0 ){
    assert( nCol==1 );
    p->azColumn[0] = "content";
  }

  /* If this is an xCreate call, create the underlying tables in the 
  ** database. TODO: For xConnect(), it could verify that said tables exist.
  */
  if( isCreate ){
    rc = fts3CreateTables(p);
    if( rc!=SQLITE_OK ) goto fts3_init_out;
  }

  rc = fts3DeclareVtab(p);
  if( rc!=SQLITE_OK ) goto fts3_init_out;

#ifdef SQLITE_TEST
  if( zTestParam ){
    p->nNodeSize = atoi(&zTestParam[5]);
  }
#endif
  *ppVTab = &p->base;

fts3_init_out:
  assert( p || (pTokenizer && rc!=SQLITE_OK) );
  if( rc!=SQLITE_OK ){
    if( p ){
      fts3DisconnectMethod((sqlite3_vtab *)p);
    }else{
      pTokenizer->pModule->xDestroy(pTokenizer);
    }
  }
  return rc;
}

/*
** The xConnect() and xCreate() methods for the virtual table. All the
** work is done in function fts3InitVtab().
*/
static int fts3ConnectMethod(
  sqlite3 *db,                    /* Database connection */
  void *pAux,                     /* Pointer to tokenizer hash table */
  int argc,                       /* Number of elements in argv array */
  const char * const *argv,       /* xCreate/xConnect argument array */
  sqlite3_vtab **ppVtab,          /* OUT: New sqlite3_vtab object */
  char **pzErr                    /* OUT: sqlite3_malloc'd error message */
){
  return fts3InitVtab(0, db, pAux, argc, argv, ppVtab, pzErr);
}
static int fts3CreateMethod(
  sqlite3 *db,                    /* Database connection */
  void *pAux,                     /* Pointer to tokenizer hash table */
  int argc,                       /* Number of elements in argv array */
  const char * const *argv,       /* xCreate/xConnect argument array */
  sqlite3_vtab **ppVtab,          /* OUT: New sqlite3_vtab object */
  char **pzErr                    /* OUT: sqlite3_malloc'd error message */
){
  return fts3InitVtab(1, db, pAux, argc, argv, ppVtab, pzErr);
}

/* 
** Implementation of the xBestIndex method for FTS3 tables. There
** are three possible strategies, in order of preference:
**
**   1. Direct lookup by rowid or docid. 
**   2. Full-text search using a MATCH operator on a non-docid column.
**   3. Linear scan of %_content table.
*/
static int fts3BestIndexMethod(sqlite3_vtab *pVTab, sqlite3_index_info *pInfo){
  Fts3Table *p = (Fts3Table *)pVTab;
  int i;                          /* Iterator variable */
  int iCons = -1;                 /* Index of constraint to use */

  /* By default use a full table scan. This is an expensive option,
  ** so search through the constraints to see if a more efficient 
  ** strategy is possible.
  */
  pInfo->idxNum = FTS3_FULLSCAN_SEARCH;
  pInfo->estimatedCost = 500000;
  for(i=0; i<pInfo->nConstraint; i++){
    struct sqlite3_index_constraint *pCons = &pInfo->aConstraint[i];
    if( pCons->usable==0 ) continue;

    /* A direct lookup on the rowid or docid column. This is the best
    ** strategy in all cases. Assign a cost of 1.0 and return early.
    */
    if( pCons->op==SQLITE_INDEX_CONSTRAINT_EQ 
     && (pCons->iColumn<0 || pCons->iColumn==p->nColumn+1 )
    ){
      pInfo->idxNum = FTS3_DOCID_SEARCH;
      pInfo->estimatedCost = 1.0;
      iCons = i;
      break;
    }

    /* A MATCH constraint. Use a full-text search.
    **
    ** If there is more than one MATCH constraint available, use the first
    ** one encountered. If there is both a MATCH constraint and a direct
    ** rowid/docid lookup, prefer the rowid/docid strategy.
    */
    if( iCons<0 
     && pCons->op==SQLITE_INDEX_CONSTRAINT_MATCH 
     && pCons->iColumn>=0 && pCons->iColumn<=p->nColumn
    ){
      pInfo->idxNum = FTS3_FULLTEXT_SEARCH + pCons->iColumn;
      pInfo->estimatedCost = 2.0;
      iCons = i;
    }
  }

  if( iCons>=0 ){
    pInfo->aConstraintUsage[iCons].argvIndex = 1;
    pInfo->aConstraintUsage[iCons].omit = 1;
  } 
  return SQLITE_OK;
}

/*
** Implementation of xOpen method.
*/
static int fts3OpenMethod(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCsr){
  sqlite3_vtab_cursor *pCsr;               /* Allocated cursor */

  UNUSED_PARAMETER(pVTab);

  /* Allocate a buffer large enough for an Fts3Cursor structure. If the
  ** allocation succeeds, zero it and return SQLITE_OK. Otherwise, 
  ** if the allocation fails, return SQLITE_NOMEM.
  */
  *ppCsr = pCsr = (sqlite3_vtab_cursor *)sqlite3_malloc(sizeof(Fts3Cursor));
  if( !pCsr ){
    return SQLITE_NOMEM;
  }
  memset(pCsr, 0, sizeof(Fts3Cursor));
  return SQLITE_OK;
}

/****************************************************************/
/****************************************************************/
/****************************************************************/
/****************************************************************/


/*
** Close the cursor.  For additional information see the documentation
** on the xClose method of the virtual table interface.
*/
static int fulltextClose(sqlite3_vtab_cursor *pCursor){
  Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;
  sqlite3_finalize(pCsr->pStmt);
  sqlite3Fts3ExprFree(pCsr->pExpr);
  sqlite3_free(pCsr->aDoclist);
  sqlite3_free(pCsr);
  return SQLITE_OK;
}

static int fts3CursorSeek(Fts3Cursor *pCsr){
  if( pCsr->isRequireSeek ){
    pCsr->isRequireSeek = 0;
    sqlite3_bind_int64(pCsr->pStmt, 1, pCsr->iPrevId);
    if( SQLITE_ROW==sqlite3_step(pCsr->pStmt) ){
      return SQLITE_OK;
    }else{
      int rc;
      pCsr->isEof = 1;
      if( SQLITE_OK==(rc = sqlite3_reset(pCsr->pStmt)) ){
        rc = SQLITE_ERROR;
      }
      return rc;
    }
  }else{
    return SQLITE_OK;
  }
}

static int fts3NextMethod(sqlite3_vtab_cursor *pCursor){
  int rc = SQLITE_OK;             /* Return code */
  Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;

  if( pCsr->aDoclist==0 ){
    if( SQLITE_ROW!=sqlite3_step(pCsr->pStmt) ){
      pCsr->isEof = 1;
      rc = sqlite3_reset(pCsr->pStmt);
    }
  }else if( pCsr->pNextId>=&pCsr->aDoclist[pCsr->nDoclist] ){
    pCsr->isEof = 1;
  }else{
    sqlite3_reset(pCsr->pStmt);
    fts3GetDeltaVarint(&pCsr->pNextId, &pCsr->iPrevId);
    pCsr->isRequireSeek = 1;
  }
  return rc;
}


/*
** The buffer pointed to by argument zNode (size nNode bytes) contains the
** root node of a b-tree segment. The segment is guaranteed to be at least
** one level high (i.e. the root node is not also a leaf). If successful,
** this function locates the leaf node of the segment that may contain the 
** term specified by arguments zTerm and nTerm and writes its block number 
** to *piLeaf.
**
** It is possible that the returned leaf node does not contain the specified
** term. However, if the segment does contain said term, it is stored on
** the identified leaf node. Because this function only inspects interior
** segment nodes (and never loads leaf nodes into memory), it is not possible
** to be sure.
**
** If an error occurs, an error code other than SQLITE_OK is returned.
*/ 
static int fts3SelectLeaf(
  Fts3Table *p,                   /* Virtual table handle */
  const char *zTerm,              /* Term to select leaves for */
  int nTerm,                      /* Size of term zTerm in bytes */
  const char *zNode,              /* Buffer containing segment interior node */
  int nNode,                      /* Size of buffer at zNode */
  sqlite3_int64 *piLeaf           /* Selected leaf node */
){
  int rc = SQLITE_OK;             /* Return code */
  const char *zCsr = zNode;       /* Cursor to iterate through node */
  const char *zEnd = &zCsr[nNode];/* End of interior node buffer */
  char *zBuffer = 0;              /* Buffer to load terms into */
  int nAlloc = 0;                 /* Size of allocated buffer */

  while( 1 ){
    int isFirstTerm = 1;          /* True when processing first term on page */
    int iHeight;                  /* Height of this node in tree */
    sqlite3_int64 iChild;         /* Block id of child node to descend to */
    int nBlock;                   /* Size of child node in bytes */

    zCsr += sqlite3Fts3GetVarint32(zCsr, &iHeight);
    zCsr += sqlite3Fts3GetVarint(zCsr, &iChild);
  
    while( zCsr<zEnd ){
      int cmp;                    /* memcmp() result */
      int nSuffix;                /* Size of term suffix */
      int nPrefix = 0;            /* Size of term prefix */
      int nBuffer;                /* Total term size */
  
      /* Load the next term on the node into zBuffer */
      if( !isFirstTerm ){
        zCsr += sqlite3Fts3GetVarint32(zCsr, &nPrefix);
      }
      isFirstTerm = 0;
      zCsr += sqlite3Fts3GetVarint32(zCsr, &nSuffix);
      if( nPrefix+nSuffix>nAlloc ){
        char *zNew;
        nAlloc = (nPrefix+nSuffix) * 2;
        zNew = (char *)sqlite3_realloc(zBuffer, nAlloc);
        if( !zNew ){
          sqlite3_free(zBuffer);
          return SQLITE_NOMEM;
        }
        zBuffer = zNew;
      }
      memcpy(&zBuffer[nPrefix], zCsr, nSuffix);
      nBuffer = nPrefix + nSuffix;
      zCsr += nSuffix;
  
      /* Compare the term we are searching for with the term just loaded from
      ** the interior node. If the specified term is greater than or equal
      ** to the term from the interior node, then all terms on the sub-tree 
      ** headed by node iChild are smaller than zTerm. No need to search 
      ** iChild.
      **
      ** If the interior node term is larger than the specified term, then
      ** the tree headed by iChild may contain the specified term.
      */
      cmp = memcmp(zTerm, zBuffer, (nBuffer>nTerm ? nTerm : nBuffer));
      if( cmp<0 || (cmp==0 && nBuffer>nTerm) ) break;
      iChild++;
    };

    /* If (iHeight==1), the children of this interior node are leaves. The
    ** specified term may be present on leaf node iChild.
    */
    if( iHeight==1 ){
      *piLeaf = iChild;
      break;
    }

    /* Descend to interior node iChild. */
    rc = sqlite3Fts3ReadBlock(p, iChild, &zCsr, &nBlock);
    if( rc!=SQLITE_OK ) break;
    zEnd = &zCsr[nBlock];
  }
  sqlite3_free(zBuffer);
  return rc;
}

/*
** This function is used to create delta-encoded serialized lists of FTS3 
** varints. Each call to this function appends a single varint to a list.
*/
static void fts3PutDeltaVarint(
  char **pp,                      /* IN/OUT: Output pointer */
  sqlite3_int64 *piPrev,          /* IN/OUT: Previous value written to list */
  sqlite3_int64 iVal              /* Write this value to the list */
){
  assert( iVal-*piPrev > 0 || (*piPrev==0 && iVal==0) );
  *pp += sqlite3Fts3PutVarint(*pp, iVal-*piPrev);
  *piPrev = iVal;
}

static void fts3PoslistCopy(char **pp, char **ppPoslist){
  char *pEnd = *ppPoslist;
  char c = 0;
  while( *pEnd | c ) c = *pEnd++ & 0x80;
  pEnd++;
  if( pp ){
    int n = (int)(pEnd - *ppPoslist);
    char *p = *pp;
    memcpy(p, *ppPoslist, n);
    p += n;
    *pp = p;
  }
  *ppPoslist = pEnd;
}

static void fts3ColumnlistCopy(char **pp, char **ppPoslist){
  char *pEnd = *ppPoslist;
  char c = 0;

  /* A column-list is terminated by either a 0x01 or 0x00. */
  while( 0xFE & (*pEnd | c) ) c = *pEnd++ & 0x80;
  if( pp ){
    int n = (int)(pEnd - *ppPoslist);
    char *p = *pp;
    memcpy(p, *ppPoslist, n);
    p += n;
    *pp = p;
  }
  *ppPoslist = pEnd;
}

/*
** Value used to signify the end of an offset-list. This is safe because
** it is not possible to have a document with 2^31 terms.
*/
#define OFFSET_LIST_END 0x7fffffff

/*
** This function is used to help parse offset-lists. When this function is
** called, *pp may point to the start of the next varint in the offset-list
** being parsed, or it may point to 1 byte past the end of the offset-list
** (in which case **pp will be 0x00 or 0x01).
**
** If *pp points past the end of the current offset list, set *pi to 
** OFFSET_LIST_END and return. Otherwise, read the next varint from *pp,
** increment the current value of *pi by the value read, and set *pp to
** point to the next value before returning.
*/
static void fts3ReadNextPos(
  char **pp,                      /* IN/OUT: Pointer into offset-list buffer */
  sqlite3_int64 *pi               /* IN/OUT: Value read from offset-list */
){
  if( **pp&0xFE ){
    fts3GetDeltaVarint(pp, pi);
    *pi -= 2;
  }else{
    *pi = OFFSET_LIST_END;
  }
}

/*
** If parameter iCol is not 0, write an 0x01 byte followed by the value of
** iCol encoded as a varint to *pp. 
**
** Set *pp to point to the byte just after the last byte written before 
** returning (do not modify it if iCol==0). Return the total number of bytes
** written (0 if iCol==0).
*/
static int fts3PutColNumber(char **pp, int iCol){
  int n = 0;                      /* Number of bytes written */
  if( iCol ){
    char *p = *pp;                /* Output pointer */
    n = 1 + sqlite3Fts3PutVarint(&p[1], iCol);
    *p = 0x01;
    *pp = &p[n];
  }
  return n;
}

/*
**
*/
static void fts3PoslistMerge(
  char **pp,                      /* Output buffer */
  char **pp1,                     /* Left input list */
  char **pp2                      /* Right input list */
){
  char *p = *pp;
  char *p1 = *pp1;
  char *p2 = *pp2;

  while( *p1 || *p2 ){
    int iCol1;
    int iCol2;

    if( *p1==0x01 ) sqlite3Fts3GetVarint32(&p1[1], &iCol1);
    else if( *p1==0x00 ) iCol1 = OFFSET_LIST_END;
    else iCol1 = 0;

    if( *p2==0x01 ) sqlite3Fts3GetVarint32(&p2[1], &iCol2);
    else if( *p2==0x00 ) iCol2 = OFFSET_LIST_END;
    else iCol2 = 0;

    if( iCol1==iCol2 ){
      sqlite3_int64 i1 = 0;
      sqlite3_int64 i2 = 0;
      sqlite3_int64 iPrev = 0;
      int n = fts3PutColNumber(&p, iCol1);
      p1 += n;
      p2 += n;

      /* At this point, both p1 and p2 point to the start of offset-lists.
      ** An offset-list is a list of non-negative delta-encoded varints, each 
      ** incremented by 2 before being stored. Each list is terminated by a 0 
      ** or 1 value (0x00 or 0x01). The following block merges the two lists
      ** and writes the results to buffer p. p is left pointing to the byte
      ** after the list written. No terminator (0x00 or 0x01) is written to
      ** the output.
      */
      fts3GetDeltaVarint(&p1, &i1);
      fts3GetDeltaVarint(&p2, &i2);
      do {
        fts3PutDeltaVarint(&p, &iPrev, (i1<i2) ? i1 : i2); 
        iPrev -= 2;
        if( i1==i2 ){
          fts3ReadNextPos(&p1, &i1);
          fts3ReadNextPos(&p2, &i2);
        }else if( i1<i2 ){
          fts3ReadNextPos(&p1, &i1);
        }else{
          fts3ReadNextPos(&p2, &i2);
        }
      }while( i1!=OFFSET_LIST_END || i2!=OFFSET_LIST_END );
    }else if( iCol1<iCol2 ){
      p1 += fts3PutColNumber(&p, iCol1);
      fts3ColumnlistCopy(&p, &p1);
    }else{
      p2 += fts3PutColNumber(&p, iCol2);
      fts3ColumnlistCopy(&p, &p2);
    }
  }

  *p++ = '\0';
  *pp = p;
  *pp1 = p1 + 1;
  *pp2 = p2 + 1;
}

/*
** nToken==1 searches for adjacent positions.
*/
static int fts3PoslistPhraseMerge(
  char **pp,                      /* Output buffer */
  int nToken,                     /* Maximum difference in token positions */
  int isSaveLeft,                 /* Save the left position */
  char **pp1,                     /* Left input list */
  char **pp2                      /* Right input list */
){
  char *p = (pp ? *pp : 0);
  char *p1 = *pp1;
  char *p2 = *pp2;

  int iCol1 = 0;
  int iCol2 = 0;
  assert( *p1!=0 && *p2!=0 );
  if( *p1==0x01 ){ 
    p1++;
    p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
  }
  if( *p2==0x01 ){ 
    p2++;
    p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
  }

  while( 1 ){
    if( iCol1==iCol2 ){
      char *pSave = p;
      sqlite3_int64 iPrev = 0;
      sqlite3_int64 iPos1 = 0;
      sqlite3_int64 iPos2 = 0;

      if( pp && iCol1 ){
        *p++ = 0x01;
        p += sqlite3Fts3PutVarint(p, iCol1);
      }

      assert( *p1!=0x00 && *p2!=0x00 && *p1!=0x01 && *p2!=0x01 );
      fts3GetDeltaVarint(&p1, &iPos1); iPos1 -= 2;
      fts3GetDeltaVarint(&p2, &iPos2); iPos2 -= 2;

      while( 1 ){
        if( iPos2>iPos1 && iPos2<=iPos1+nToken ){
          sqlite3_int64 iSave;
          if( !pp ){
            fts3PoslistCopy(0, &p2);
            fts3PoslistCopy(0, &p1);
            *pp1 = p1;
            *pp2 = p2;
            return 1;
          }
          iSave = isSaveLeft ? iPos1 : iPos2;
          fts3PutDeltaVarint(&p, &iPrev, iSave+2); iPrev -= 2;
          pSave = 0;
        }
        if( (!isSaveLeft && iPos2<=(iPos1+nToken)) || iPos2<=iPos1 ){
          if( (*p2&0xFE)==0 ) break;
          fts3GetDeltaVarint(&p2, &iPos2); iPos2 -= 2;
        }else{
          if( (*p1&0xFE)==0 ) break;
          fts3GetDeltaVarint(&p1, &iPos1); iPos1 -= 2;
        }

      }
      if( pSave && pp ){
        p = pSave;
      }

      fts3ColumnlistCopy(0, &p1);
      fts3ColumnlistCopy(0, &p2);
      assert( (*p1&0xFE)==0 && (*p2&0xFE)==0 );
      if( 0==*p1 || 0==*p2 ) break;

      p1++;
      p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
      p2++;
      p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
    }

    /* Advance pointer p1 or p2 (whichever corresponds to the smaller of
    ** iCol1 and iCol2) so that it points to either the 0x00 that marks the
    ** end of the position list, or the 0x01 that precedes the next 
    ** column-number in the position list. 
    */
    else if( iCol1<iCol2 ){
      fts3ColumnlistCopy(0, &p1);
      if( 0==*p1 ) break;
      p1++;
      p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
    }else{
      fts3ColumnlistCopy(0, &p2);
      if( 0==*p2 ) break;
      p2++;
      p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
    }
  }

  fts3PoslistCopy(0, &p2);
  fts3PoslistCopy(0, &p1);
  *pp1 = p1;
  *pp2 = p2;
  if( !pp || *pp==p ){
    return 0;
  }
  *p++ = 0x00;
  *pp = p;
  return 1;
}

/*
** Merge two position-lists as required by the NEAR operator.
*/
static int fts3PoslistNearMerge(
  char **pp,                      /* Output buffer */
  char *aTmp,                     /* Temporary buffer space */
  int nRight,                     /* Maximum difference in token positions */
  int nLeft,                      /* Maximum difference in token positions */
  char **pp1,                     /* IN/OUT: Left input list */
  char **pp2                      /* IN/OUT: Right input list */
){
  char *p1 = *pp1;
  char *p2 = *pp2;

  if( !pp ){
    if( fts3PoslistPhraseMerge(0, nRight, 0, pp1, pp2) ) return 1;
    *pp1 = p1;
    *pp2 = p2;
    return fts3PoslistPhraseMerge(0, nLeft, 0, pp2, pp1);
  }else{
    char *pTmp1 = aTmp;
    char *pTmp2;
    char *aTmp2;
    int res = 1;

    fts3PoslistPhraseMerge(&pTmp1, nRight, 0, pp1, pp2);
    aTmp2 = pTmp2 = pTmp1;
    *pp1 = p1;
    *pp2 = p2;
    fts3PoslistPhraseMerge(&pTmp2, nLeft, 1, pp2, pp1);
    if( pTmp1!=aTmp && pTmp2!=aTmp2 ){
      fts3PoslistMerge(pp, &aTmp, &aTmp2);
    }else if( pTmp1!=aTmp ){
      fts3PoslistCopy(pp, &aTmp);
    }else if( pTmp2!=aTmp2 ){
      fts3PoslistCopy(pp, &aTmp2);
    }else{
      res = 0;
    }

    return res;
  }
}

/*
** Values that may be used as the first parameter to fts3DoclistMerge().
*/
#define MERGE_NOT        2        /* D + D -> D */
#define MERGE_AND        3        /* D + D -> D */
#define MERGE_OR         4        /* D + D -> D */
#define MERGE_POS_OR     5        /* P + P -> P */
#define MERGE_PHRASE     6        /* P + P -> D */
#define MERGE_POS_PHRASE 7        /* P + P -> P */
#define MERGE_NEAR       8        /* P + P -> D */
#define MERGE_POS_NEAR   9        /* P + P -> P */

/*
** Merge the two doclists passed in buffer a1 (size n1 bytes) and a2
** (size n2 bytes). The output is written to pre-allocated buffer aBuffer,
** which is guaranteed to be large enough to hold the results. The number
** of bytes written to aBuffer is stored in *pnBuffer before returning.
**
** If successful, SQLITE_OK is returned. Otherwise, if a malloc error
** occurs while allocating a temporary buffer as part of the merge operation,
** SQLITE_NOMEM is returned.
*/
static int fts3DoclistMerge(
  int mergetype,                  /* One of the MERGE_XXX constants */
  int nParam1,                    /* Used by MERGE_NEAR and MERGE_POS_NEAR */
  int nParam2,                    /* Used by MERGE_NEAR and MERGE_POS_NEAR */
  char *aBuffer,                  /* Pre-allocated output buffer */
  int *pnBuffer,                  /* OUT: Bytes written to aBuffer */
  char *a1,                       /* Buffer containing first doclist */
  int n1,                         /* Size of buffer a1 */
  char *a2,                       /* Buffer containing second doclist */
  int n2                          /* Size of buffer a2 */
){
  sqlite3_int64 i1 = 0;
  sqlite3_int64 i2 = 0;
  sqlite3_int64 iPrev = 0;

  char *p = aBuffer;
  char *p1 = a1;
  char *p2 = a2;
  char *pEnd1 = &a1[n1];
  char *pEnd2 = &a2[n2];

  assert( mergetype==MERGE_OR     || mergetype==MERGE_POS_OR 
       || mergetype==MERGE_AND    || mergetype==MERGE_NOT
       || mergetype==MERGE_PHRASE || mergetype==MERGE_POS_PHRASE
       || mergetype==MERGE_NEAR   || mergetype==MERGE_POS_NEAR
  );

  if( !aBuffer ){
    return SQLITE_NOMEM;
  }
  if( n1==0 && n2==0 ){
    *pnBuffer = 0;
    return SQLITE_OK;
  }

  /* Read the first docid from each doclist */
  fts3GetDeltaVarint2(&p1, pEnd1, &i1);
  fts3GetDeltaVarint2(&p2, pEnd2, &i2);

  switch( mergetype ){
    case MERGE_OR:
    case MERGE_POS_OR:
      while( p1 || p2 ){
        if( p2 && p1 && i1==i2 ){
          fts3PutDeltaVarint(&p, &iPrev, i1);
          if( mergetype==MERGE_POS_OR ) fts3PoslistMerge(&p, &p1, &p2);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( !p2 || (p1 && i1<i2) ){
          fts3PutDeltaVarint(&p, &iPrev, i1);
          if( mergetype==MERGE_POS_OR ) fts3PoslistCopy(&p, &p1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3PutDeltaVarint(&p, &iPrev, i2);
          if( mergetype==MERGE_POS_OR ) fts3PoslistCopy(&p, &p2);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      break;

    case MERGE_AND:
      while( p1 && p2 ){
        if( i1==i2 ){
          fts3PutDeltaVarint(&p, &iPrev, i1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( i1<i2 ){
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      break;

    case MERGE_NOT:
      while( p1 ){
        if( p2 && i1==i2 ){
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( !p2 || i1<i2 ){
          fts3PutDeltaVarint(&p, &iPrev, i1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      break;

    case MERGE_POS_PHRASE:
    case MERGE_PHRASE: {
      char **ppPos = (mergetype==MERGE_PHRASE ? 0 : &p);
      while( p1 && p2 ){
        if( i1==i2 ){
          char *pSave = p;
          sqlite3_int64 iPrevSave = iPrev;
          fts3PutDeltaVarint(&p, &iPrev, i1);
          if( 0==fts3PoslistPhraseMerge(ppPos, 1, 0, &p1, &p2) ){
            p = pSave;
            iPrev = iPrevSave;
          }
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( i1<i2 ){
          fts3PoslistCopy(0, &p1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3PoslistCopy(0, &p2);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      break;
    }

    default: assert( mergetype==MERGE_POS_NEAR || mergetype==MERGE_NEAR ); {
      char *aTmp = 0;
      char **ppPos = 0;
      if( mergetype==MERGE_POS_NEAR ){
        ppPos = &p;
        aTmp = sqlite3_malloc(2*(n1+n2));
        if( !aTmp ){
          return SQLITE_NOMEM;
        }
      }

      while( p1 && p2 ){
        if( i1==i2 ){
          char *pSave = p;
          sqlite3_int64 iPrevSave = iPrev;
          fts3PutDeltaVarint(&p, &iPrev, i1);

          if( !fts3PoslistNearMerge(ppPos, aTmp, nParam1, nParam2, &p1, &p2) ){
            iPrev = iPrevSave;
            p = pSave;
          }

          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }else if( i1<i2 ){
          fts3PoslistCopy(0, &p1);
          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
        }else{
          fts3PoslistCopy(0, &p2);
          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
        }
      }
      sqlite3_free(aTmp);
      break;
    }
  }

  *pnBuffer = (int)(p-aBuffer);
  return SQLITE_OK;
}

/* 
** A pointer to an instance of this structure is used as the context 
** argument to sqlite3Fts3SegReaderIterate()
*/
typedef struct TermSelect TermSelect;
struct TermSelect {
  int isReqPos;
  char *aOutput;                  /* Malloc'd output buffer */
  int nOutput;                    /* Size of output in bytes */
};

/*
** This function is used as the sqlite3Fts3SegReaderIterate() callback when
** querying the full-text index for a doclist associated with a term or
** term-prefix.
*/
static int fts3TermSelectCb(
  Fts3Table *p,                   /* Virtual table object */
  void *pContext,                 /* Pointer to TermSelect structure */
  char *zTerm,
  int nTerm,
  char *aDoclist,
  int nDoclist
){
  TermSelect *pTS = (TermSelect *)pContext;
  int nNew = pTS->nOutput + nDoclist;
  char *aNew = sqlite3_malloc(nNew);

  UNUSED_PARAMETER(p);
  UNUSED_PARAMETER(zTerm);
  UNUSED_PARAMETER(nTerm);

  if( !aNew ){
    return SQLITE_NOMEM;
  }

  if( pTS->nOutput==0 ){
    /* If this is the first term selected, copy the doclist to the output
    ** buffer using memcpy(). TODO: Add a way to transfer control of the
    ** aDoclist buffer from the caller so as to avoid the memcpy().
    */
    memcpy(aNew, aDoclist, nDoclist);
  }else{
    /* The output buffer is not empty. Merge doclist aDoclist with the
    ** existing output. This can only happen with prefix-searches (as
    ** searches for exact terms return exactly one doclist).
    */
    int mergetype = (pTS->isReqPos ? MERGE_POS_OR : MERGE_OR);
    fts3DoclistMerge(mergetype, 0, 0,
        aNew, &nNew, pTS->aOutput, pTS->nOutput, aDoclist, nDoclist
    );
  }

  sqlite3_free(pTS->aOutput);
  pTS->aOutput = aNew;
  pTS->nOutput = nNew;

  return SQLITE_OK;
}

/*
** This function retreives the doclist for the specified term (or term
** prefix) from the database. 
**
** The returned doclist may be in one of two formats, depending on the 
** value of parameter isReqPos. If isReqPos is zero, then the doclist is
** a sorted list of delta-compressed docids. If isReqPos is non-zero, 
** then the returned list is in the same format as is stored in the
** database without the found length specifier at the start of on-disk
** doclists.
*/
static int fts3TermSelect(
  Fts3Table *p,                   /* Virtual table handle */
  int iColumn,                    /* Column to query (or -ve for all columns) */
  const char *zTerm,              /* Term to query for */
  int nTerm,                      /* Size of zTerm in bytes */
  int isPrefix,                   /* True for a prefix search */
  int isReqPos,                   /* True to include position lists in output */
  int *pnOut,                     /* OUT: Size of buffer at *ppOut */
  char **ppOut                    /* OUT: Malloced result buffer */
){
  int i;
  TermSelect tsc;
  Fts3SegFilter filter;           /* Segment term filter configuration */
  Fts3SegReader **apSegment = 0;  /* Array of segments to read data from */
  int nSegment = 0;               /* Size of apSegment array */
  int nAlloc = 0;                 /* Allocated size of segment array */
  int rc;                         /* Return code */
  sqlite3_stmt *pStmt;            /* SQL statement to scan %_segdir table */
  int iAge = 0;                   /* Used to assign ages to segments */

  /* Loop through the entire %_segdir table. For each segment, create a
  ** Fts3SegReader to iterate through the subset of the segment leaves
  ** that may contain a term that matches zTerm/nTerm. For non-prefix
  ** searches, this is always a single leaf. For prefix searches, this
  ** may be a contiguous block of leaves.
  **
  ** The code in this loop does not actually load any leaves into memory
  ** (unless the root node happens to be a leaf). It simply examines the
  ** b-tree structure to determine which leaves need to be inspected.
  */
  rc = sqlite3Fts3AllSegdirs(p, &pStmt);
  while( rc==SQLITE_OK && SQLITE_ROW==(rc = sqlite3_step(pStmt)) ){
    Fts3SegReader *pNew = 0;
    int nRoot = sqlite3_column_bytes(pStmt, 4);
    char const *zRoot = sqlite3_column_blob(pStmt, 4);
    if( sqlite3_column_int64(pStmt, 1)==0 ){
      /* The entire segment is stored on the root node (which must be a
      ** leaf). Do not bother inspecting any data in this case, just
      ** create a Fts3SegReader to scan the single leaf. 
      */
      rc = sqlite3Fts3SegReaderNew(p, iAge, 0, 0, 0, zRoot, nRoot, &pNew);
    }else{
      int rc2;                    /* Return value of sqlite3Fts3ReadBlock() */
      sqlite3_int64 i1;           /* Blockid of leaf that may contain zTerm */
      rc = fts3SelectLeaf(p, zTerm, nTerm, zRoot, nRoot, &i1);
      if( rc==SQLITE_OK ){
        sqlite3_int64 i2 = sqlite3_column_int64(pStmt, 2);
        rc = sqlite3Fts3SegReaderNew(p, iAge, i1, i2, 0, 0, 0, &pNew);
      }

      /* The following call to ReadBlock() serves to reset the SQL statement
      ** used to retrieve blocks of data from the %_segments table. If it is
      ** not reset here, then it may remain classified as an active statement 
      ** by SQLite, which may lead to "DROP TABLE" or "DETACH" commands 
      ** failing.
      */ 
      rc2 = sqlite3Fts3ReadBlock(p, 0, 0, 0);
      if( rc==SQLITE_OK ){
        rc = rc2;
      }
    }
    iAge++;

    /* If a new Fts3SegReader was allocated, add it to the apSegment array. */
    assert( pNew!=0 || rc!=SQLITE_OK );
    if( pNew ){
      if( nSegment==nAlloc ){
        Fts3SegReader **pArray;
        nAlloc += 16;
        pArray = (Fts3SegReader **)sqlite3_realloc(
            apSegment, nAlloc*sizeof(Fts3SegReader *)
        );
        if( !pArray ){
          sqlite3Fts3SegReaderFree(p, pNew);
          rc = SQLITE_NOMEM;
          goto finished;
        }
        apSegment = pArray;
      }
      apSegment[nSegment++] = pNew;
    }
  }
  if( rc!=SQLITE_DONE ){
    assert( rc!=SQLITE_OK );
    goto finished;
  }

  memset(&tsc, 0, sizeof(TermSelect));
  tsc.isReqPos = isReqPos;

  filter.flags = FTS3_SEGMENT_IGNORE_EMPTY 
        | (isPrefix ? FTS3_SEGMENT_PREFIX : 0)
        | (isReqPos ? FTS3_SEGMENT_REQUIRE_POS : 0)
        | (iColumn<p->nColumn ? FTS3_SEGMENT_COLUMN_FILTER : 0);
  filter.iCol = iColumn;
  filter.zTerm = zTerm;
  filter.nTerm = nTerm;

  rc = sqlite3Fts3SegReaderIterate(p, apSegment, nSegment, &filter,
      fts3TermSelectCb, (void *)&tsc
  );

  if( rc==SQLITE_OK ){
    *ppOut = tsc.aOutput;
    *pnOut = tsc.nOutput;
  }else{
    sqlite3_free(tsc.aOutput);
  }

finished:
  sqlite3_reset(pStmt);
  for(i=0; i<nSegment; i++){
    sqlite3Fts3SegReaderFree(p, apSegment[i]);
  }
  sqlite3_free(apSegment);
  return rc;
}


/* 
** Return a DocList corresponding to the phrase *pPhrase.
*/
static int fts3PhraseSelect(
  Fts3Table *p,                   /* Virtual table handle */
  Fts3Phrase *pPhrase,            /* Phrase to return a doclist for */
  int isReqPos,                   /* True if output should contain positions */
  char **paOut,                   /* OUT: Pointer to malloc'd result buffer */
  int *pnOut                      /* OUT: Size of buffer at *paOut */
){
  char *pOut = 0;
  int nOut = 0;
  int rc = SQLITE_OK;
  int ii;
  int iCol = pPhrase->iColumn;
  int isTermPos = (pPhrase->nToken>1 || isReqPos);

  assert( p->nPendingData==0 );

  for(ii=0; ii<pPhrase->nToken; ii++){
    struct PhraseToken *pTok = &pPhrase->aToken[ii];
    char *z = pTok->z;            /* Next token of the phrase */
    int n = pTok->n;              /* Size of z in bytes */
    int isPrefix = pTok->isPrefix;/* True if token is a prefix */
    char *pList;                  /* Pointer to token doclist */
    int nList;                    /* Size of buffer at pList */

    rc = fts3TermSelect(p, iCol, z, n, isPrefix, isTermPos, &nList, &pList);
    if( rc!=SQLITE_OK ) break;

    if( ii==0 ){
      pOut = pList;
      nOut = nList;
    }else{
      /* Merge the new term list and the current output. If this is the
      ** last term in the phrase, and positions are not required in the
      ** output of this function, the positions can be dropped as part
      ** of this merge. Either way, the result of this merge will be
      ** smaller than nList bytes. The code in fts3DoclistMerge() is written
      ** so that it is safe to use pList as the output as well as an input
      ** in this case.
      */
      int mergetype = MERGE_POS_PHRASE;
      if( ii==pPhrase->nToken-1 && !isReqPos ){
        mergetype = MERGE_PHRASE;
      }
      fts3DoclistMerge(mergetype, 0, 0, pList, &nOut, pOut, nOut, pList, nList);
      sqlite3_free(pOut);
      pOut = pList;
    }
  }

  if( rc==SQLITE_OK ){
    *paOut = pOut;
    *pnOut = nOut;
  }else{
    sqlite3_free(pOut);
  }
  return rc;
}

/*
** Evaluate the full-text expression pExpr against fts3 table pTab. Store
** the resulting doclist in *paOut and *pnOut.
*/
static int evalFts3Expr(
  Fts3Table *p,                   /* Virtual table handle */
  Fts3Expr *pExpr,                /* Parsed fts3 expression */
  char **paOut,                   /* OUT: Pointer to malloc'd result buffer */
  int *pnOut                      /* OUT: Size of buffer at *paOut */
){
  int rc = SQLITE_OK;             /* Return code */


  /* Zero the output parameters. */
  *paOut = 0;
  *pnOut = 0;


  if( pExpr ){
    if( pExpr->eType==FTSQUERY_PHRASE ){

      int isReqPos = (pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR);



      rc = fts3PhraseSelect(p, pExpr->pPhrase, isReqPos, paOut, pnOut);
    }else{
      char *aLeft;
      char *aRight;
      int nLeft;
      int nRight;



      if( SQLITE_OK==(rc = evalFts3Expr(p, pExpr->pRight, &aRight, &nRight))
       && SQLITE_OK==(rc = evalFts3Expr(p, pExpr->pLeft, &aLeft, &nLeft))
      ){
        assert( pExpr->eType==FTSQUERY_NEAR || pExpr->eType==FTSQUERY_OR     
            || pExpr->eType==FTSQUERY_AND  || pExpr->eType==FTSQUERY_NOT
        );
        switch( pExpr->eType ){
          case FTSQUERY_NEAR: {

            Fts3Expr *pLeft;
            Fts3Expr *pRight;
            int mergetype = MERGE_NEAR;
            int nParam1;
            int nParam2;
            char *aBuffer;
           
            if( pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR ){

              mergetype = MERGE_POS_NEAR;
            }
            pLeft = pExpr->pLeft;
            while( pLeft->eType==FTSQUERY_NEAR ){ 
              pLeft=pLeft->pRight;
            }
            pRight = pExpr->pRight;
            assert( pRight->eType==FTSQUERY_PHRASE );
            assert( pLeft->eType==FTSQUERY_PHRASE );



            nParam1 = pExpr->nNear+1;
            nParam2 = nParam1+pLeft->pPhrase->nToken+pRight->pPhrase->nToken-2;
            aBuffer = sqlite3_malloc(nLeft+nRight+1);
            rc = fts3DoclistMerge(mergetype, nParam1, nParam2, aBuffer,
                pnOut, aLeft, nLeft, aRight, nRight
            );

            if( rc!=SQLITE_OK ){
              sqlite3_free(aBuffer);
            }else{
              *paOut = aBuffer;
            }


            sqlite3_free(aLeft);
            break;
          }

          case FTSQUERY_OR: {

            /* Allocate a buffer for the output. The maximum size is the
            ** sum of the sizes of the two input buffers. The +1 term is
            ** so that a buffer of zero bytes is never allocated - this can
            ** cause fts3DoclistMerge() to incorrectly return SQLITE_NOMEM.
            */
            char *aBuffer = sqlite3_malloc(nRight+nLeft+1);
            rc = fts3DoclistMerge(MERGE_OR, 0, 0, aBuffer, pnOut,
                aLeft, nLeft, aRight, nRight
            );
            *paOut = aBuffer;
            sqlite3_free(aLeft);
            break;
          }



          default: {
            assert( FTSQUERY_NOT==MERGE_NOT && FTSQUERY_AND==MERGE_AND );
            fts3DoclistMerge(pExpr->eType, 0, 0, aLeft, pnOut,
                aLeft, nLeft, aRight, nRight
            );
            *paOut = aLeft;
            break;
          }
        }
      }
      sqlite3_free(aRight);

    }
  }

  return rc;
}















































/*
** This is the xFilter interface for the virtual table.  See
** the virtual table xFilter method documentation for additional
** information.
**
** If idxNum==FTS3_FULLSCAN_SEARCH then do a full table scan against
** the %_content table.
**
** If idxNum==FTS3_DOCID_SEARCH then do a docid lookup for a single entry
** in the %_content table.
**
** If idxNum>=FTS3_FULLTEXT_SEARCH then use the full text index.  The
** column on the left-hand side of the MATCH operator is column
** number idxNum-FTS3_FULLTEXT_SEARCH, 0 indexed.  argv[0] is the right-hand
** side of the MATCH operator.
*/
/* TODO(shess) Upgrade the cursor initialization and destruction to
** account for fts3FilterMethod() being called multiple times on the
** same cursor. The current solution is very fragile. Apply fix to
** fts3 as appropriate.
*/
static int fts3FilterMethod(
  sqlite3_vtab_cursor *pCursor,   /* The cursor used for this query */
  int idxNum,                     /* Strategy index */
  const char *idxStr,             /* Unused */
  int nVal,                       /* Number of elements in apVal */
  sqlite3_value **apVal           /* Arguments for the indexing scheme */
){
  const char *azSql[] = {
    "SELECT * FROM %Q.'%q_content' WHERE docid = ?", /* non-full-table-scan */
    "SELECT * FROM %Q.'%q_content'",                 /* full-table-scan */
  };
  int rc;                         /* Return code */
  char *zSql;                     /* SQL statement used to access %_content */
  Fts3Table *p = (Fts3Table *)pCursor->pVtab;
  Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;

  UNUSED_PARAMETER(idxStr);
  UNUSED_PARAMETER(nVal);

  assert( idxNum>=0 && idxNum<=(FTS3_FULLTEXT_SEARCH+p->nColumn) );
  assert( nVal==0 || nVal==1 );
  assert( (nVal==0)==(idxNum==FTS3_FULLSCAN_SEARCH) );

  /* In case the cursor has been used before, clear it now. */
  sqlite3_finalize(pCsr->pStmt);
  sqlite3_free(pCsr->aDoclist);
  memset(&pCursor[1], 0, sizeof(Fts3Cursor)-sizeof(sqlite3_vtab_cursor));

  /* Compile a SELECT statement for this cursor. For a full-table-scan, the
  ** statement loops through all rows of the %_content table. For a
  ** full-text query or docid lookup, the statement retrieves a single
  ** row by docid.
  */
  zSql = sqlite3_mprintf(azSql[idxNum==FTS3_FULLSCAN_SEARCH], p->zDb, p->zName);
  if( !zSql ){
    rc = SQLITE_NOMEM;
  }else{
    rc = sqlite3_prepare_v2(p->db, zSql, -1, &pCsr->pStmt, 0);
    sqlite3_free(zSql);
  }
  if( rc!=SQLITE_OK ) return rc;
  pCsr->eSearch = (i16)idxNum;

  if( idxNum==FTS3_DOCID_SEARCH ){
    rc = sqlite3_bind_value(pCsr->pStmt, 1, apVal[0]);
  }else if( idxNum!=FTS3_FULLSCAN_SEARCH ){
    int iCol = idxNum-FTS3_FULLTEXT_SEARCH;
    const char *zQuery = (const char *)sqlite3_value_text(apVal[0]);

    if( zQuery==0 && sqlite3_value_type(apVal[0])!=SQLITE_NULL ){
      return SQLITE_NOMEM;
    }
    rc = sqlite3Fts3PendingTermsFlush(p);
    if( rc!=SQLITE_OK ) return rc;

    rc = sqlite3Fts3ExprParse(p->pTokenizer, p->azColumn, p->nColumn, 
        iCol, zQuery, -1, &pCsr->pExpr
    );
    if( rc!=SQLITE_OK ) return rc;

    rc = evalFts3Expr(p, pCsr->pExpr, &pCsr->aDoclist, &pCsr->nDoclist);
    pCsr->pNextId = pCsr->aDoclist;
    pCsr->iPrevId = 0;
  }

  if( rc!=SQLITE_OK ) return rc;
  return fts3NextMethod(pCursor);
}

/* 
** This is the xEof method of the virtual table. SQLite calls this 
** routine to find out if it has reached the end of a result set.
*/
static int fts3EofMethod(sqlite3_vtab_cursor *pCursor){
  return ((Fts3Cursor *)pCursor)->isEof;
}

/* 
** This is the xRowid method. The SQLite core calls this routine to
** retrieve the rowid for the current row of the result set. fts3
** exposes %_content.docid as the rowid for the virtual table. The
** rowid should be written to *pRowid.
*/
static int fts3RowidMethod(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
  Fts3Cursor *pCsr = (Fts3Cursor *) pCursor;
  if( pCsr->aDoclist ){
    *pRowid = pCsr->iPrevId;
  }else{
    *pRowid = sqlite3_column_int64(pCsr->pStmt, 0);
  }
  return SQLITE_OK;
}

/* 
** This is the xColumn method, called by SQLite to request a value from
** the row that the supplied cursor currently points to.
*/
static int fts3ColumnMethod(
  sqlite3_vtab_cursor *pCursor,   /* Cursor to retrieve value from */
  sqlite3_context *pContext,      /* Context for sqlite3_result_xxx() calls */
  int iCol                        /* Index of column to read value from */
){
  int rc;                         /* Return Code */
  Fts3Cursor *pCsr = (Fts3Cursor *) pCursor;
  Fts3Table *p = (Fts3Table *)pCursor->pVtab;

  /* The column value supplied by SQLite must be in range. */
  assert( iCol>=0 && iCol<=p->nColumn+1 );

  rc = fts3CursorSeek(pCsr);
  if( rc==SQLITE_OK ){
    if( iCol==p->nColumn+1 ){
      /* This call is a request for the "docid" column. Since "docid" is an 
      ** alias for "rowid", use the xRowid() method to obtain the value.
      */
      sqlite3_int64 iRowid;
      rc = fts3RowidMethod(pCursor, &iRowid);
      sqlite3_result_int64(pContext, iRowid);
    }else if( iCol==p->nColumn ){
      /* The extra column whose name is the same as the table.
      ** Return a blob which is a pointer to the cursor.
      */
      sqlite3_result_blob(pContext, &pCsr, sizeof(pCsr), SQLITE_TRANSIENT);
    }else{
      sqlite3_result_value(pContext, sqlite3_column_value(pCsr->pStmt, iCol+1));
    }
  }
  return rc;
}

/* 
** This function is the implementation of the xUpdate callback used by 
** FTS3 virtual tables. It is invoked by SQLite each time a row is to be
** inserted, updated or deleted.
*/
static int fts3UpdateMethod(
  sqlite3_vtab *pVtab,            /* Virtual table handle */
  int nArg,                       /* Size of argument array */
  sqlite3_value **apVal,          /* Array of arguments */
  sqlite_int64 *pRowid            /* OUT: The affected (or effected) rowid */
){
  return sqlite3Fts3UpdateMethod(pVtab, nArg, apVal, pRowid);
}

/*
** Implementation of xSync() method. Flush the contents of the pending-terms
** hash-table to the database.
*/
static int fts3SyncMethod(sqlite3_vtab *pVtab){
  return sqlite3Fts3PendingTermsFlush((Fts3Table *)pVtab);
}

/*
** Implementation of xBegin() method. This is a no-op.
*/
static int fts3BeginMethod(sqlite3_vtab *pVtab){
  UNUSED_PARAMETER(pVtab);
  assert( ((Fts3Table *)pVtab)->nPendingData==0 );
  return SQLITE_OK;
}

/*
** Implementation of xCommit() method. This is a no-op. The contents of
** the pending-terms hash-table have already been flushed into the database
** by fts3SyncMethod().
*/
static int fts3CommitMethod(sqlite3_vtab *pVtab){
  UNUSED_PARAMETER(pVtab);
  assert( ((Fts3Table *)pVtab)->nPendingData==0 );
  return SQLITE_OK;
}

/*
** Implementation of xRollback(). Discard the contents of the pending-terms
** hash-table. Any changes made to the database are reverted by SQLite.
*/
static int fts3RollbackMethod(sqlite3_vtab *pVtab){
  sqlite3Fts3PendingTermsClear((Fts3Table *)pVtab);
  return SQLITE_OK;
}

/*
** Helper function used by the implementation of the overloaded snippet(),
** offsets() and optimize() SQL functions.
**
** If the value passed as the third argument is a blob of size
** sizeof(Fts3Cursor*), then the blob contents are copied to the 
** output variable *ppCsr and SQLITE_OK is returned. Otherwise, an error
** message is written to context pContext and SQLITE_ERROR returned. The
** string passed via zFunc is used as part of the error message.
*/
static int fts3FunctionArg(
  sqlite3_context *pContext,      /* SQL function call context */
  const char *zFunc,              /* Function name */
  sqlite3_value *pVal,            /* argv[0] passed to function */
  Fts3Cursor **ppCsr         /* OUT: Store cursor handle here */
){
  Fts3Cursor *pRet;
  if( sqlite3_value_type(pVal)!=SQLITE_BLOB 
   || sqlite3_value_bytes(pVal)!=sizeof(Fts3Cursor *)
  ){
    char *zErr = sqlite3_mprintf("illegal first argument to %s", zFunc);
    sqlite3_result_error(pContext, zErr, -1);
    sqlite3_free(zErr);
    return SQLITE_ERROR;
  }
  memcpy(&pRet, sqlite3_value_blob(pVal), sizeof(Fts3Cursor *));
  *ppCsr = pRet;
  return SQLITE_OK;
}

/*
** Implementation of the snippet() function for FTS3
*/
static void fts3SnippetFunc(
  sqlite3_context *pContext,      /* SQLite function call context */
  int nVal,                       /* Size of apVal[] array */
  sqlite3_value **apVal           /* Array of arguments */
){
  Fts3Cursor *pCsr;               /* Cursor handle passed through apVal[0] */
  const char *zStart = "<b>";
  const char *zEnd = "</b>";
  const char *zEllipsis = "<b>...</b>";

  /* There must be at least one argument passed to this function (otherwise
  ** the non-overloaded version would have been called instead of this one).
  */
  assert( nVal>=1 );

  if( nVal>4 ){
    sqlite3_result_error(pContext, 
        "wrong number of arguments to function snippet()", -1);
    return;
  }
  if( fts3FunctionArg(pContext, "snippet", apVal[0], &pCsr) ) return;

  switch( nVal ){
    case 4: zEllipsis = (const char*)sqlite3_value_text(apVal[3]);
    case 3: zEnd = (const char*)sqlite3_value_text(apVal[2]);
    case 2: zStart = (const char*)sqlite3_value_text(apVal[1]);
  }

  sqlite3Fts3Snippet(pContext, pCsr, zStart, zEnd, zEllipsis);






























































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































}

/*
** Implementation of the offsets() function for FTS3
*/
static void fts3OffsetsFunc(
  sqlite3_context *pContext,      /* SQLite function call context */
  int nVal,                       /* Size of argument array */
  sqlite3_value **apVal           /* Array of arguments */
){
  Fts3Cursor *pCsr;               /* Cursor handle passed through apVal[0] */












  UNUSED_PARAMETER(nVal);





































































































































































































































  assert( nVal==1 );










  if( fts3FunctionArg(pContext, "offsets", apVal[0], &pCsr) ) return;
  assert( pCsr );

  sqlite3Fts3Offsets(pContext, pCsr);
}








/* 


















** Implementation of the special optimize() function for FTS3. This 
** function merges all segments in the database to a single segment.
** Example usage is:
**













**   SELECT optimize(t) FROM t LIMIT 1;
**













** where 't' is the name of an FTS3 table.
*/

























































































static void fts3OptimizeFunc(
  sqlite3_context *pContext,      /* SQLite function call context */
  int nVal,                       /* Size of argument array */
  sqlite3_value **apVal           /* Array of arguments */
){






































































































  int rc;                         /* Return code */


  Fts3Table *p;                   /* Virtual table handle */
  Fts3Cursor *pCursor;            /* Cursor handle passed through apVal[0] */









  UNUSED_PARAMETER(nVal);





  assert( nVal==1 );







  if( fts3FunctionArg(pContext, "optimize", apVal[0], &pCursor) ) return;
  p = (Fts3Table *)pCursor->base.pVtab;
  assert( p );











































































  rc = sqlite3Fts3Optimize(p);


















  switch( rc ){
    case SQLITE_OK:



      sqlite3_result_text(pContext, "Index optimized", -1, SQLITE_STATIC);
      break;
    case SQLITE_DONE:






















      sqlite3_result_text(pContext, "Index already optimal", -1, SQLITE_STATIC);
      break;
    default:
      sqlite3_result_error_code(pContext, rc);
      break;
  }











}






/*
** This routine implements the xFindFunction method for the FTS3
** virtual table.
*/
static int fts3FindFunctionMethod(
  sqlite3_vtab *pVtab,            /* Virtual table handle */

  int nArg,                       /* Number of SQL function arguments */
  const char *zName,              /* Name of SQL function */
  void (**pxFunc)(sqlite3_context*,int,sqlite3_value**), /* OUT: Result */
  void **ppArg                    /* Unused */
){




  struct Overloaded {
    const char *zName;
    void (*xFunc)(sqlite3_context*,int,sqlite3_value**);
  } aOverload[] = {
    { "snippet", fts3SnippetFunc },
    { "offsets", fts3OffsetsFunc },

    { "optimize", fts3OptimizeFunc },
  };
  int i;                          /* Iterator variable */

  UNUSED_PARAMETER(pVtab);
  UNUSED_PARAMETER(nArg);
  UNUSED_PARAMETER(ppArg);

  for(i=0; i<SizeofArray(aOverload); i++){
    if( strcmp(zName, aOverload[i].zName)==0 ){
      *pxFunc = aOverload[i].xFunc;
      return 1;














    }
  }

  /* No function of the specified name was found. Return 0. */
  return 0;
}

/*
** Implementation of FTS3 xRename method. Rename an fts3 table.
*/
static int fts3RenameMethod(
  sqlite3_vtab *pVtab,            /* Virtual table handle */
  const char *zName               /* New name of table */
){
  Fts3Table *p = (Fts3Table *)pVtab;     
  int rc = SQLITE_NOMEM;          /* Return Code */
  char *zSql;                     /* SQL script to run to rename tables */
 
  zSql = sqlite3_mprintf(
    "ALTER TABLE %Q.'%q_content'  RENAME TO '%q_content';"
    "ALTER TABLE %Q.'%q_segments' RENAME TO '%q_segments';"
    "ALTER TABLE %Q.'%q_segdir'   RENAME TO '%q_segdir';"
    , p->zDb, p->zName, zName 
    , p->zDb, p->zName, zName 
    , p->zDb, p->zName, zName
  );
................................................................................
    sqlite3_free(zSql);
  }
  return rc;
}

static const sqlite3_module fts3Module = {
  /* iVersion      */ 0,
  /* xCreate       */ fts3CreateMethod,
  /* xConnect      */ fts3ConnectMethod,
  /* xBestIndex    */ fts3BestIndexMethod,
  /* xDisconnect   */ fts3DisconnectMethod,
  /* xDestroy      */ fts3DestroyMethod,
  /* xOpen         */ fts3OpenMethod,
  /* xClose        */ fulltextClose,
  /* xFilter       */ fts3FilterMethod,
  /* xNext         */ fts3NextMethod,
  /* xEof          */ fts3EofMethod,
  /* xColumn       */ fts3ColumnMethod,
  /* xRowid        */ fts3RowidMethod,
  /* xUpdate       */ fts3UpdateMethod,
  /* xBegin        */ fts3BeginMethod,
  /* xSync         */ fts3SyncMethod,
  /* xCommit       */ fts3CommitMethod,
  /* xRollback     */ fts3RollbackMethod,
  /* xFindFunction */ fts3FindFunctionMethod,
  /* xRename */       fts3RenameMethod,
};

/*
** This function is registered as the module destructor (called when an
** FTS3 enabled database connection is closed). It frees the memory
** allocated for the tokenizer hash table.
*/
static void hashDestroy(void *p){
  Fts3Hash *pHash = (Fts3Hash *)p;
  sqlite3Fts3HashClear(pHash);
  sqlite3_free(pHash);
}

/*
** The fts3 built-in tokenizers - "simple" and "porter" - are implemented
** in files fts3_tokenizer1.c and fts3_porter.c respectively. The following
................................................................................
** Function ...PorterTokenizerModule() sets *pModule to point to the
** porter tokenizer/stemmer implementation.
*/
void sqlite3Fts3SimpleTokenizerModule(sqlite3_tokenizer_module const**ppModule);
void sqlite3Fts3PorterTokenizerModule(sqlite3_tokenizer_module const**ppModule);
void sqlite3Fts3IcuTokenizerModule(sqlite3_tokenizer_module const**ppModule);



/*
** Initialise the fts3 extension. If this extension is built as part
** of the sqlite library, then this function is called directly by
** SQLite. If fts3 is built as a dynamically loadable extension, this
** function is called by the sqlite3_extension_init() entry point.
*/
int sqlite3Fts3Init(sqlite3 *db){
  int rc = SQLITE_OK;
  Fts3Hash *pHash = 0;
  const sqlite3_tokenizer_module *pSimple = 0;
  const sqlite3_tokenizer_module *pPorter = 0;
  const sqlite3_tokenizer_module *pIcu = 0;

  sqlite3Fts3SimpleTokenizerModule(&pSimple);
  sqlite3Fts3PorterTokenizerModule(&pPorter);
#ifdef SQLITE_ENABLE_ICU
  sqlite3Fts3IcuTokenizerModule(&pIcu);
#endif

  /* Allocate and initialise the hash-table used to store tokenizers. */
  pHash = sqlite3_malloc(sizeof(Fts3Hash));
  if( !pHash ){
    rc = SQLITE_NOMEM;
  }else{
    sqlite3Fts3HashInit(pHash, FTS3_HASH_STRING, 1);
  }

  /* Load the built-in tokenizers into the hash table */
................................................................................
  /* Create the virtual table wrapper around the hash-table and overload 
  ** the two scalar functions. If this is successful, register the
  ** module with sqlite.
  */
  if( SQLITE_OK==rc 
   && SQLITE_OK==(rc = sqlite3Fts3InitHashTable(db, pHash, "fts3_tokenizer"))
   && SQLITE_OK==(rc = sqlite3_overload_function(db, "snippet", -1))
   && SQLITE_OK==(rc = sqlite3_overload_function(db, "offsets", 1))
   && SQLITE_OK==(rc = sqlite3_overload_function(db, "optimize", 1))




  ){
    return sqlite3_create_module_v2(
        db, "fts3", &fts3Module, (void *)pHash, hashDestroy
    );
  }

  /* An error has occurred. Delete the hash table and return the error code. */
................................................................................
  const sqlite3_api_routines *pApi
){
  SQLITE_EXTENSION_INIT2(pApi)
  return sqlite3Fts3Init(db);
}
#endif

#endif

/*
** 2009 Nov 12
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
*/

#ifndef _FTSINT_H
#define _FTSINT_H

#if !defined(NDEBUG) && !defined(SQLITE_DEBUG) 
# define NDEBUG 1
#endif

#include "sqlite3.h"
#include "fts3_tokenizer.h"
#include "fts3_hash.h"

/*
** This constant controls how often segments are merged. Once there are
** FTS3_MERGE_COUNT segments of level N, they are merged into a single
** segment of level N+1.
*/
#define FTS3_MERGE_COUNT 16

/*
** This is the maximum amount of data (in bytes) to store in the 
** Fts3Table.pendingTerms hash table. Normally, the hash table is
** populated as documents are inserted/updated/deleted in a transaction
** and used to create a new segment when the transaction is committed.
** However if this limit is reached midway through a transaction, a new 
** segment is created and the hash table cleared immediately.
*/
#define FTS3_MAX_PENDING_DATA (1*1024*1024)

/*
** Macro to return the number of elements in an array. SQLite has a
** similar macro called ArraySize(). Use a different name to avoid
** a collision when building an amalgamation with built-in FTS3.
*/
#define SizeofArray(X) ((int)(sizeof(X)/sizeof(X[0])))

/*
** Maximum length of a varint encoded integer. The varint format is different
** from that used by SQLite, so the maximum length is 10, not 9.
*/
#define FTS3_VARINT_MAX 10

/*
** This section provides definitions to allow the
** FTS3 extension to be compiled outside of the 
** amalgamation.
*/
#ifndef SQLITE_AMALGAMATION
/*
** Macros indicating that conditional expressions are always true or
** false.
*/
# define ALWAYS(x) (x)
# define NEVER(X)  (x)
/*
** Internal types used by SQLite.
*/
typedef unsigned char u8;         /* 1-byte (or larger) unsigned integer */
typedef short int i16;            /* 2-byte (or larger) signed integer */
/*
** Macro used to suppress compiler warnings for unused parameters.
*/
#define UNUSED_PARAMETER(x) (void)(x)
#endif

typedef struct Fts3Table Fts3Table;
typedef struct Fts3Cursor Fts3Cursor;
typedef struct Fts3Expr Fts3Expr;
typedef struct Fts3Phrase Fts3Phrase;
typedef struct Fts3SegReader Fts3SegReader;
typedef struct Fts3SegFilter Fts3SegFilter;

/*
** A connection to a fulltext index is an instance of the following
** structure. The xCreate and xConnect methods create an instance
** of this structure and xDestroy and xDisconnect free that instance.
** All other methods receive a pointer to the structure as one of their
** arguments.
*/
struct Fts3Table {
  sqlite3_vtab base;              /* Base class used by SQLite core */
  sqlite3 *db;                    /* The database connection */
  const char *zDb;                /* logical database name */
  const char *zName;              /* virtual table name */
  int nColumn;                    /* number of named columns in virtual table */
  char **azColumn;                /* column names.  malloced */
  sqlite3_tokenizer *pTokenizer;  /* tokenizer for inserts and queries */

  /* Precompiled statements used by the implementation. Each of these 
  ** statements is run and reset within a single virtual table API call. 
  */
  sqlite3_stmt *aStmt[18];

  /* Pointer to string containing the SQL:
  **
  ** "SELECT block FROM %_segments WHERE blockid BETWEEN ? AND ? 
  **    ORDER BY blockid"
  */
  char *zSelectLeaves;
  int nLeavesStmt;                /* Valid statements in aLeavesStmt */
  int nLeavesTotal;               /* Total number of prepared leaves stmts */
  int nLeavesAlloc;               /* Allocated size of aLeavesStmt */
  sqlite3_stmt **aLeavesStmt;     /* Array of prepared zSelectLeaves stmts */

  int nNodeSize;                  /* Soft limit for node size */

  /* The following hash table is used to buffer pending index updates during
  ** transactions. Variable nPendingData estimates the memory size of the 
  ** pending data, including hash table overhead, but not malloc overhead. 
  ** When nPendingData exceeds FTS3_MAX_PENDING_DATA, the buffer is flushed 
  ** automatically. Variable iPrevDocid is the docid of the most recently
  ** inserted record.
  */
  int nPendingData;
  sqlite_int64 iPrevDocid;
  Fts3Hash pendingTerms;
};

/*
** When the core wants to read from the virtual table, it creates a
** virtual table cursor (an instance of the following structure) using
** the xOpen method. Cursors are destroyed using the xClose method.
*/
struct Fts3Cursor {
  sqlite3_vtab_cursor base;       /* Base class used by SQLite core */
  i16 eSearch;                    /* Search strategy (see below) */
  u8 isEof;                       /* True if at End Of Results */
  u8 isRequireSeek;               /* True if must seek pStmt to %_content row */
  sqlite3_stmt *pStmt;            /* Prepared statement in use by the cursor */
  Fts3Expr *pExpr;                /* Parsed MATCH query string */
  sqlite3_int64 iPrevId;          /* Previous id read from aDoclist */
  char *pNextId;                  /* Pointer into the body of aDoclist */
  char *aDoclist;                 /* List of docids for full-text queries */
  int nDoclist;                   /* Size of buffer at aDoclist */
};

/*
** The Fts3Cursor.eSearch member is always set to one of the following.
** Actualy, Fts3Cursor.eSearch can be greater than or equal to
** FTS3_FULLTEXT_SEARCH.  If so, then Fts3Cursor.eSearch - 2 is the index
** of the column to be searched.  For example, in
**
**     CREATE VIRTUAL TABLE ex1 USING fts3(a,b,c,d);
**     SELECT docid FROM ex1 WHERE b MATCH 'one two three';
** 
** Because the LHS of the MATCH operator is 2nd column "b",
** Fts3Cursor.eSearch will be set to FTS3_FULLTEXT_SEARCH+1.  (+0 for a,
** +1 for b, +2 for c, +3 for d.)  If the LHS of MATCH were "ex1" 
** indicating that all columns should be searched,
** then eSearch would be set to FTS3_FULLTEXT_SEARCH+4.
*/
#define FTS3_FULLSCAN_SEARCH 0    /* Linear scan of %_content table */
#define FTS3_DOCID_SEARCH    1    /* Lookup by rowid on %_content table */
#define FTS3_FULLTEXT_SEARCH 2    /* Full-text index search */

/*
** A "phrase" is a sequence of one or more tokens that must match in
** sequence.  A single token is the base case and the most common case.
** For a sequence of tokens contained in "...", nToken will be the number
** of tokens in the string.
*/
struct Fts3Phrase {
  int nToken;                /* Number of tokens in the phrase */
  int iColumn;               /* Index of column this phrase must match */
  int isNot;                 /* Phrase prefixed by unary not (-) operator */
  struct PhraseToken {
    char *z;                 /* Text of the token */
    int n;                   /* Number of bytes in buffer pointed to by z */
    int isPrefix;            /* True if token ends in with a "*" character */
  } aToken[1];               /* One entry for each token in the phrase */
};

/*
** A tree of these objects forms the RHS of a MATCH operator.
*/
struct Fts3Expr {
  int eType;                 /* One of the FTSQUERY_XXX values defined below */
  int nNear;                 /* Valid if eType==FTSQUERY_NEAR */
  Fts3Expr *pParent;         /* pParent->pLeft==this or pParent->pRight==this */
  Fts3Expr *pLeft;           /* Left operand */
  Fts3Expr *pRight;          /* Right operand */
  Fts3Phrase *pPhrase;       /* Valid if eType==FTSQUERY_PHRASE */
};

/*
** Candidate values for Fts3Query.eType. Note that the order of the first
** four values is in order of precedence when parsing expressions. For 
** example, the following:
**
**   "a OR b AND c NOT d NEAR e"
**
** is equivalent to:
**
**   "a OR (b AND (c NOT (d NEAR e)))"
*/
#define FTSQUERY_NEAR   1
#define FTSQUERY_NOT    2
#define FTSQUERY_AND    3
#define FTSQUERY_OR     4
#define FTSQUERY_PHRASE 5


/* fts3_init.c */
int sqlite3Fts3DeleteVtab(int, sqlite3_vtab *);
int sqlite3Fts3InitVtab(int, sqlite3*, void*, int, const char*const*, 
                        sqlite3_vtab **, char **);

/* fts3_write.c */
int sqlite3Fts3UpdateMethod(sqlite3_vtab*,int,sqlite3_value**,sqlite3_int64*);
int sqlite3Fts3PendingTermsFlush(Fts3Table *);
void sqlite3Fts3PendingTermsClear(Fts3Table *);
int sqlite3Fts3Optimize(Fts3Table *);
int sqlite3Fts3SegReaderNew(Fts3Table *,int, sqlite3_int64,
  sqlite3_int64, sqlite3_int64, const char *, int, Fts3SegReader**);
void sqlite3Fts3SegReaderFree(Fts3Table *, Fts3SegReader *);
int sqlite3Fts3SegReaderIterate(
  Fts3Table *, Fts3SegReader **, int, Fts3SegFilter *,
  int (*)(Fts3Table *, void *, char *, int, char *, int),  void *
);
int sqlite3Fts3ReadBlock(Fts3Table*, sqlite3_int64, char const**, int*);
int sqlite3Fts3AllSegdirs(Fts3Table*, sqlite3_stmt **);

/* Flags allowed as part of the 4th argument to SegmentReaderIterate() */
#define FTS3_SEGMENT_REQUIRE_POS   0x00000001
#define FTS3_SEGMENT_IGNORE_EMPTY  0x00000002
#define FTS3_SEGMENT_COLUMN_FILTER 0x00000004
#define FTS3_SEGMENT_PREFIX        0x00000008

/* Type passed as 4th argument to SegmentReaderIterate() */
struct Fts3SegFilter {
  const char *zTerm;
  int nTerm;
  int iCol;
  int flags;
};

/* fts3.c */
int sqlite3Fts3PutVarint(char *, sqlite3_int64);
int sqlite3Fts3GetVarint(const char *, sqlite_int64 *);
int sqlite3Fts3GetVarint32(const char *, int *);
int sqlite3Fts3VarintLen(sqlite3_uint64);
void sqlite3Fts3Dequote(char *);

/* fts3_tokenizer.c */
const char *sqlite3Fts3NextToken(const char *, int *);
int sqlite3Fts3InitHashTable(sqlite3 *, Fts3Hash *, const char *);
int sqlite3Fts3InitTokenizer(Fts3Hash *pHash, 
  const char *, sqlite3_tokenizer **, const char **, char **
);

/* fts3_snippet.c */
void sqlite3Fts3Offsets(sqlite3_context*, Fts3Cursor*);
void sqlite3Fts3Snippet(sqlite3_context*, Fts3Cursor*, 
  const char *, const char *, const char *
);

/* fts3_expr.c */
int sqlite3Fts3ExprParse(sqlite3_tokenizer *, 
  char **, int, int, const char *, int, Fts3Expr **
);
void sqlite3Fts3ExprFree(Fts3Expr *);
#ifdef SQLITE_TEST
void sqlite3Fts3ExprInitTestInterface(sqlite3 *db);
#endif

#endif /* _FTSINT_H */