SQLite

#include "fts3.h"
#ifndef SQLITE_CORE 
# include "sqlite3ext.h"
  SQLITE_EXTENSION_INIT1
#endif

static int fts3EvalNext(Fts3Cursor *pCsr);
static int fts3EvalStart(Fts3Cursor *pCsr);
static int fts3TermSegReaderCursor(
    Fts3Cursor *, const char *, int, int, Fts3MultiSegReader **);

/* 
** 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;

  for(i=0; i<p->nColumn; i++){
    fts3Appendf(pRc, &zRet, ",%s(?)", zFunction);
  }
  sqlite3_free(zFree);
  return zRet;
}

/*
** This function interprets the string at (*pp) as a non-negative integer
** value. It reads the integer and sets *pnOut to the value read, then 
** sets *pp to point to the byte immediately following the last byte of
** the integer value.
**
** Only decimal digits ('0'..'9') may be part of an integer value. 
**
** If *pp does not being with a decimal digit SQLITE_ERROR is returned and
** the output value undefined. Otherwise SQLITE_OK is returned.
**
** This function is used when parsing the "prefix=" FTS4 parameter.
*/
static int fts3GobbleInt(const char **pp, int *pnOut){
  const char *p = *pp;
  int nInt = 0;
  const char *p = *pp;            /* Iterator pointer */
  int nInt = 0;                   /* Output value */

  for(p=*pp; p[0]>='0' && p[0]<='9'; p++){
    nInt = nInt * 10 + (p[0] - '0');
  }
  if( p==*pp ) return SQLITE_ERROR;
  *pnOut = nInt;
  *pp = p;
  return SQLITE_OK;
}


/*
** This function is called to allocate an array of Fts3Index structures
** representing the indexes maintained by the current FTS table. FTS tables
** always maintain the main "terms" index, but may also maintain one or
** more "prefix" indexes, depending on the value of the "prefix=" parameter
** (if any) specified as part of the CREATE VIRTUAL TABLE statement.
**
** Argument zParam is passed the value of the "prefix=" option if one was
** specified, or NULL otherwise.
**
** If no error occurs, SQLITE_OK is returned and *apIndex set to point to
** the allocated array. *pnIndex is set to the number of elements in the
** array. If an error does occur, an SQLite error code is returned.
**
** Regardless of whether or not an error is returned, it is the responsibility
** of the caller to call sqlite3_free() on the output array to free it.
*/
static int fts3PrefixParameter(
  const char *zParam,             /* ABC in prefix=ABC parameter to parse */
  int *pnIndex,                   /* OUT: size of *apIndex[] array */
  struct Fts3Index **apIndex,     /* OUT: Array of indexes for this table */
  struct Fts3Index **apIndex      /* OUT: Array of indexes for this table */
  struct Fts3Index **apFree       /* OUT: Free this with sqlite3_free() */
){
  struct Fts3Index *aIndex;
  int nIndex = 1;
  struct Fts3Index *aIndex;       /* Allocated array */
  int nIndex = 1;                 /* Number of entries in array */

  if( zParam && zParam[0] ){
    const char *p;
    nIndex++;
    for(p=zParam; *p; p++){
      if( *p==',' ) nIndex++;
    }
  }

  aIndex = sqlite3_malloc(sizeof(struct Fts3Index) * nIndex);
  *apIndex = *apFree = aIndex;
  *apIndex = aIndex;
  *pnIndex = nIndex;
  if( !aIndex ){
    return SQLITE_NOMEM;
  }

  memset(aIndex, 0, sizeof(struct Fts3Index) * nIndex);
  if( zParam ){

  int nDb;                        /* Bytes required to hold database name */
  int nName;                      /* Bytes required to hold table name */
  int isFts4 = (argv[0][3]=='4'); /* True for FTS4, false for FTS3 */
  const char **aCol;              /* Array of column names */
  sqlite3_tokenizer *pTokenizer = 0;        /* Tokenizer for this table */

  int nIndex;                     /* Size of aIndex[] array */
  struct Fts3Index *aIndex;       /* Array of indexes for this table */
  struct Fts3Index *aIndex = 0;   /* Array of indexes for this table */
  struct Fts3Index *aFree = 0;    /* Free this before returning */

  /* The results of parsing supported FTS4 key=value options: */
  int bNoDocsize = 0;             /* True to omit %_docsize table */
  int bDescIdx = 0;               /* True to store descending indexes */
  char *zPrefix = 0;              /* Prefix parameter value (or NULL) */
  char *zCompress = 0;            /* compress=? parameter (or NULL) */
  char *zUncompress = 0;          /* uncompress=? parameter (or NULL) */

  if( pTokenizer==0 ){
    rc = sqlite3Fts3InitTokenizer(pHash, "simple", &pTokenizer, pzErr);
    if( rc!=SQLITE_OK ) goto fts3_init_out;
  }
  assert( pTokenizer );

  rc = fts3PrefixParameter(zPrefix, &nIndex, &aIndex, &aFree);
  rc = fts3PrefixParameter(zPrefix, &nIndex, &aIndex);
  if( rc==SQLITE_ERROR ){
    assert( zPrefix );
    *pzErr = sqlite3_mprintf("error parsing prefix parameter: %s", zPrefix);
  }
  if( rc!=SQLITE_OK ) goto fts3_init_out;

  /* Allocate and populate the Fts3Table structure. */

  p->nNodeSize = p->nPgsz-35;

  /* Declare the table schema to SQLite. */
  fts3DeclareVtab(&rc, p);

fts3_init_out:
  sqlite3_free(zPrefix);
  sqlite3_free(aFree);
  sqlite3_free(aIndex);
  sqlite3_free(zCompress);
  sqlite3_free(zUncompress);
  sqlite3_free((void *)aCol);
  if( rc!=SQLITE_OK ){
    if( p ){
      fts3DisconnectMethod((sqlite3_vtab *)p);
    }else if( pTokenizer ){

  *p++ = POS_END;
  *pp = p;
  *pp1 = p1 + 1;
  *pp2 = p2 + 1;
}

/*
** nToken==1 searches for adjacent positions.
**
** This function is used to merge two position lists into one. When it is
** called, *pp1 and *pp2 must both point to position lists. A position-list is
** the part of a doclist that follows each document id. For example, if a row
** contains:
**
**     'a b c'|'x y z'|'a b b a'
**
** Then the position list for this row for token 'b' would consist of:
**
**     0x02 0x01 0x02 0x03 0x03 0x00
**
** When this function returns, both *pp1 and *pp2 are left pointing to the
** byte following the 0x00 terminator of their respective position lists.
**
** If isSaveLeft is 0, an entry is added to the output position list for 
** each position in *pp2 for which there exists one or more positions in
** *pp1 so that (pos(*pp2)>pos(*pp1) && pos(*pp2)-pos(*pp1)<=nToken). i.e.
** when the *pp1 token appears before the *pp2 token, but not more than nToken
** slots before it.
**
** e.g. nToken==1 searches for adjacent positions.
*/
static int fts3PoslistPhraseMerge(
  char **pp,                      /* IN/OUT: Preallocated output buffer */
  int nToken,                     /* Maximum difference in token positions */
  int isSaveLeft,                 /* Save the left position */
  int isExact,                    /* If *pp1 is exactly nTokens before *pp2 */
  char **pp1,                     /* IN/OUT: Left input list */

    res = 0;
  }

  return res;
}

/* 
** A pointer to an instance of this structure is used as the context 
** argument to sqlite3Fts3SegReaderIterate()
** An instance of this function is used to merge together the (potentially
** large number of) doclists for each term that matches a prefix query.
** See function fts3TermSelectMerge() for details.
*/
typedef struct TermSelect TermSelect;
struct TermSelect {
  int isReqPos;
  char *aaOutput[16];             /* Malloc'd output buffer */
  int anOutput[16];               /* Size of output in bytes */
  char *aaOutput[16];             /* Malloc'd output buffers */
  int anOutput[16];               /* Size each output buffer in bytes */
};


/*
** This function is used to read a single varint from a buffer. Parameter
** pEnd points 1 byte past the end of the buffer. When this function is
** called, if *pp points to pEnd or greater, then the end of the buffer
** has been reached. In this case *pp is set to 0 and the function returns.
**
** If *pp does not point to or past pEnd, then a single varint is read
** from *pp. *pp is then set to point 1 byte past the end of the read varint.
**
** If bDescIdx is false, the value read is added to *pVal before returning.
** If it is true, the value read is subtracted from *pVal before this 
** function returns.
*/
static void fts3GetDeltaVarint3(
  char **pp, 
  char *pEnd, 
  int bDescIdx,
  sqlite3_int64 *pVal
  char **pp,                      /* IN/OUT: Point to read varint from */
  char *pEnd,                     /* End of buffer */
  int bDescIdx,                   /* True if docids are descending */
  sqlite3_int64 *pVal             /* IN/OUT: Integer value */
){
  if( *pp>=pEnd ){
    *pp = 0;
  }else{
    sqlite3_int64 iVal;
    *pp += sqlite3Fts3GetVarint(*pp, &iVal);
    if( bDescIdx ){
      *pVal -= iVal;
    }else{
      *pVal += iVal;
    }
  }
}

/*
** This function is used to write a single varint to a buffer. The varint
** is written to *pp. Before returning, *pp is set to point 1 byte past the
** end of the value written.
**
** If *pbFirst is zero when this function is called, the value written to
** the buffer is that of parameter iVal. 
**
** If *pbFirst is non-zero when this function is called, then the value 
** written is either (iVal-*piPrev) (if bDescIdx is zero) or (*piPrev-iVal)
** (if bDescIdx is non-zero).
**
** Before returning, this function always sets *pbFirst to 1 and *piPrev
** to the value of parameter iVal.
*/
static void fts3PutDeltaVarint3(
  char **pp,                      /* IN/OUT: Output pointer */
  int bDescIdx,                   /* True for descending docids */
  sqlite3_int64 *piPrev,          /* IN/OUT: Previous value written to list */
  int *pbFirst,                   /* IN/OUT: True after first int written */
  sqlite3_int64 iVal              /* Write this value to the list */
){
  sqlite3_int64 iWrite;
  if( bDescIdx==0 || *pbFirst==0 ){
    iWrite = iVal - *piPrev;
  }else{
    iWrite = *piPrev - iVal;
  }
  assert( *pbFirst || *piPrev==0 );
  assert( *pbFirst==0 || iWrite>0 );
  *pp += sqlite3Fts3PutVarint(*pp, iWrite);
  *piPrev = iVal;
  *pbFirst = 1;
}

#define COMPARE_DOCID(i1, i2) ((bDescIdx?-1:1) * (i1-i2))

/*
** This macro is used by various functions that merge doclists. The two
** arguments are 64-bit docid values. If the value of the stack variable
** bDescDoclist is 0 when this macro is invoked, then it returns (i1-i2). 
** Otherwise, (i2-i1).
**
** Using this makes it easier to write code that can merge doclists that are
** sorted in either ascending or descending order.
*/
#define DOCID_CMP(i1, i2) ((bDescDoclist?-1:1) * (i1-i2))

/*
** This function does an "OR" merge of two doclists (output contains all
** positions contained in either argument doclist). If the docids in the 
** input doclists are sorted in ascending order, parameter bDescDoclist
** should be false. If they are sorted in ascending order, it should be
** passed a non-zero value.
**
** If no error occurs, *paOut is set to point at an sqlite3_malloc'd buffer
** containing the output doclist and SQLITE_OK is returned. In this case
** *pnOut is set to the number of bytes in the output doclist.
**
** If an error occurs, an SQLite error code is returned. The output values
** are undefined in this case.
*/
static int fts3DoclistOrMerge(
  int bDescIdx,                   /* True if arguments are desc */
  int bDescDoclist,               /* True if arguments are desc */
  char *a1, int n1,               /* First doclist */
  char *a2, int n2,               /* Second doclist */
  char **paOut, int *pnOut        /* OUT: Malloc'd doclist */
){
  sqlite3_int64 i1 = 0;
  sqlite3_int64 i2 = 0;
  sqlite3_int64 iPrev = 0;

  aOut = sqlite3_malloc(n1+n2);
  if( !aOut ) return SQLITE_NOMEM;

  p = aOut;
  fts3GetDeltaVarint3(&p1, pEnd1, 0, &i1);
  fts3GetDeltaVarint3(&p2, pEnd2, 0, &i2);
  while( p1 || p2 ){
    sqlite3_int64 iDiff = COMPARE_DOCID(i1, i2);
    sqlite3_int64 iDiff = DOCID_CMP(i1, i2);

    if( p2 && p1 && iDiff==0 ){
      fts3PutDeltaVarint3(&p, bDescIdx, &iPrev, &bFirstOut, i1);
      fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i1);
      fts3PoslistMerge(&p, &p1, &p2);
      fts3GetDeltaVarint3(&p1, pEnd1, bDescIdx, &i1);
      fts3GetDeltaVarint3(&p2, pEnd2, bDescIdx, &i2);
      fts3GetDeltaVarint3(&p1, pEnd1, bDescDoclist, &i1);
      fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
    }else if( !p2 || (p1 && iDiff<0) ){
      fts3PutDeltaVarint3(&p, bDescIdx, &iPrev, &bFirstOut, i1);
      fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i1);
      fts3PoslistCopy(&p, &p1);
      fts3GetDeltaVarint3(&p1, pEnd1, bDescIdx, &i1);
      fts3GetDeltaVarint3(&p1, pEnd1, bDescDoclist, &i1);
    }else{
      fts3PutDeltaVarint3(&p, bDescIdx, &iPrev, &bFirstOut, i2);
      fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i2);
      fts3PoslistCopy(&p, &p2);
      fts3GetDeltaVarint3(&p2, pEnd2, bDescIdx, &i2);
      fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
    }
  }

  *paOut = aOut;
  *pnOut = (p-aOut);
  return SQLITE_OK;
}

/*
** This function does a "phrase" merge of two doclists. In a phrase merge,
** the output contains a copy of each position from the right-hand input
** doclist for which there is a position in the left-hand input doclist
** exactly nDist tokens before it.
**
** If the docids in the input doclists are sorted in ascending order,
** parameter bDescDoclist should be false. If they are sorted in ascending 
** order, it should be passed a non-zero value.
**
** The right-hand input doclist is overwritten by this function.
*/
static void fts3DoclistPhraseMerge(
  int bDescIdx,                   /* True if arguments are desc */
  int bDescDoclist,               /* True if arguments are desc */
  int nDist,                      /* Distance from left to right (1=adjacent) */
  char *aLeft, int nLeft,         /* Left doclist */
  char *aRight, int *pnRight      /* IN/OUT: Right/output doclist */
){
  sqlite3_int64 i1 = 0;
  sqlite3_int64 i2 = 0;
  sqlite3_int64 iPrev = 0;

  assert( nDist>0 );

  p = aOut;
  fts3GetDeltaVarint3(&p1, pEnd1, 0, &i1);
  fts3GetDeltaVarint3(&p2, pEnd2, 0, &i2);

  while( p1 && p2 ){
    sqlite3_int64 iDiff = COMPARE_DOCID(i1, i2);
    sqlite3_int64 iDiff = DOCID_CMP(i1, i2);
    if( iDiff==0 ){
      char *pSave = p;
      sqlite3_int64 iPrevSave = iPrev;
      int bFirstOutSave = bFirstOut;

      fts3PutDeltaVarint3(&p, bDescIdx, &iPrev, &bFirstOut, i1);
      fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i1);
      if( 0==fts3PoslistPhraseMerge(&p, nDist, 0, 1, &p1, &p2) ){
        p = pSave;
        iPrev = iPrevSave;
        bFirstOut = bFirstOutSave;
      }
      fts3GetDeltaVarint3(&p1, pEnd1, bDescIdx, &i1);
      fts3GetDeltaVarint3(&p2, pEnd2, bDescIdx, &i2);
      fts3GetDeltaVarint3(&p1, pEnd1, bDescDoclist, &i1);
      fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
    }else if( iDiff<0 ){
      fts3PoslistCopy(0, &p1);
      fts3GetDeltaVarint3(&p1, pEnd1, bDescIdx, &i1);
      fts3GetDeltaVarint3(&p1, pEnd1, bDescDoclist, &i1);
    }else{
      fts3PoslistCopy(0, &p2);
      fts3GetDeltaVarint3(&p2, pEnd2, bDescIdx, &i2);
      fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
    }
  }

  *pnRight = p - aOut;
}


/*
** Merge all doclists in the TermSelect.aaOutput[] array into a single
** doclist stored in TermSelect.aaOutput[0]. If successful, delete all
** other doclists (except the aaOutput[0] one) and return SQLITE_OK.
**
** If an OOM error occurs, return SQLITE_NOMEM. In this case it is
** the responsibility of the caller to free any doclists left in the
** TermSelect.aaOutput[] array.
*/
static int fts3TermSelectMerge(Fts3Table *p, TermSelect *pTS){
static int fts3TermSelectFinishMerge(Fts3Table *p, TermSelect *pTS){
  char *aOut = 0;
  int nOut = 0;
  int i;

  /* Loop through the doclists in the aaOutput[] array. Merge them all
  ** into a single doclist.
  */

  pTS->aaOutput[0] = aOut;
  pTS->anOutput[0] = nOut;
  return SQLITE_OK;
}

/*
** Merge the doclist aDoclist/nDoclist into the TermSelect object passed
** as the first argument. The merge is an "OR" merge (see function
** fts3DoclistOrMerge() for details).
**
** This function is used as the sqlite3Fts3SegReaderIterate() callback when
** querying the full-text index for a doclist associated with a term or
** term-prefix.
** This function is called with the doclist for each term that matches
** a queried prefix. It merges all these doclists into one, the doclist
** for the specified prefix. Since there can be a very large number of
** doclists to merge, the merging is done pair-wise using the TermSelect
** object.
**
** This function returns SQLITE_OK if the merge is successful, or an
** SQLite error code (SQLITE_NOMEM) if an error occurs.
*/
static int fts3TermSelectCb(
  Fts3Table *p,                   /* Virtual table object */
  void *pContext,                 /* Pointer to TermSelect structure */
static int fts3TermSelectMerge(
  Fts3Table *p,                   /* FTS table handle */
  TermSelect *pTS,                /* TermSelect object to merge into */
  char *zTerm,
  int nTerm,
  char *aDoclist,
  int nDoclist
  char *aDoclist,                 /* Pointer to doclist */
  int nDoclist                    /* Size of aDoclist in bytes */
){
  TermSelect *pTS = (TermSelect *)pContext;

  UNUSED_PARAMETER(p);
  UNUSED_PARAMETER(zTerm);
  UNUSED_PARAMETER(nTerm);

  if( pTS->aaOutput[0]==0 ){
    /* If this is the first term selected, copy the doclist to the output
    ** buffer using memcpy(). */
    pTS->aaOutput[0] = sqlite3_malloc(nDoclist);
    pTS->anOutput[0] = nDoclist;
    if( pTS->aaOutput[0] ){
      memcpy(pTS->aaOutput[0], aDoclist, nDoclist);

    }
    pCsr->apSegment = apNew;
  }
  pCsr->apSegment[pCsr->nSegment++] = pNew;
  return SQLITE_OK;
}

/*
** Add seg-reader objects to the Fts3MultiSegReader object passed as the
** 8th argument.
**
** This function returns SQLITE_OK if successful, or an SQLite error code
** otherwise.
*/
static int fts3SegReaderCursor(
  Fts3Table *p,                   /* FTS3 table handle */
  int iIndex,                     /* Index to search (from 0 to p->nIndex-1) */
  int iLevel,                     /* Level of segments to scan */
  const char *zTerm,              /* Term to query for */
  int nTerm,                      /* Size of zTerm in bytes */
  int isPrefix,                   /* True for a prefix search */
  int isScan,                     /* True to scan from zTerm to EOF */
  Fts3MultiSegReader *pCsr       /* Cursor object to populate */
  Fts3MultiSegReader *pCsr        /* Cursor object to populate */
){
  int rc = SQLITE_OK;
  int rc = SQLITE_OK;             /* Error code */
  int rc2;
  sqlite3_stmt *pStmt = 0;
  sqlite3_stmt *pStmt = 0;        /* Statement to iterate through segments */
  int rc2;                        /* Result of sqlite3_reset() */

  /* If iLevel is less than 0 and this is not a scan, include a seg-reader 
  ** for the pending-terms. If this is a scan, then this call must be being
  ** made by an fts4aux module, not an FTS table. In this case calling
  ** Fts3SegReaderPending might segfault, as the data structures used by 
  ** fts4aux are not completely populated. So it's easiest to filter these
  ** calls out here.  */

  memset(pCsr, 0, sizeof(Fts3MultiSegReader));

  return fts3SegReaderCursor(
      p, iIndex, iLevel, zTerm, nTerm, isPrefix, isScan, pCsr
  );
}

/*
** In addition to its current configuration, have the Fts3MultiSegReader
** passed as the 4th argument also scan the doclist for term zTerm/nTerm.
**
** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
*/
static int fts3SegReaderCursorAddZero(
  Fts3Table *p,
  const char *zTerm,
  int nTerm,
  Fts3MultiSegReader *pCsr
  Fts3Table *p,                   /* FTS virtual table handle */
  const char *zTerm,              /* Term to scan doclist of */
  int nTerm,                      /* Number of bytes in zTerm */
  Fts3MultiSegReader *pCsr        /* Fts3MultiSegReader to modify */
){
  return fts3SegReaderCursor(p, 0, FTS3_SEGCURSOR_ALL, zTerm, nTerm, 0, 0,pCsr);
}


int sqlite3Fts3TermSegReaderCursor(
/*
** Open an Fts3MultiSegReader to scan the doclist for term zTerm/nTerm. Or,
** if isPrefix is true, to scan the doclist for all terms for which 
** zTerm/nTerm is a prefix. If successful, return SQLITE_OK and write
** a pointer to the new Fts3MultiSegReader to *ppSegcsr. Otherwise, return
** an SQLite error code.
**
** It is the responsibility of the caller to free this object by eventually
** passing it to fts3SegReaderCursorFree() 
**
** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
** Output parameter *ppSegcsr is set to 0 if an error occurs.
*/
static int fts3TermSegReaderCursor(
  Fts3Cursor *pCsr,               /* Virtual table cursor handle */
  const char *zTerm,              /* Term to query for */
  int nTerm,                      /* Size of zTerm in bytes */
  int isPrefix,                   /* True for a prefix search */
  Fts3MultiSegReader **ppSegcsr   /* OUT: Allocated seg-reader cursor */
){
  Fts3MultiSegReader *pSegcsr;   /* Object to allocate and return */
  Fts3MultiSegReader *pSegcsr;    /* Object to allocate and return */
  int rc = SQLITE_NOMEM;          /* Return code */

  pSegcsr = sqlite3_malloc(sizeof(Fts3MultiSegReader));
  if( pSegcsr ){
    int i;
    int bFound = 0;               /* True once an index has been found */
    Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;

    }
  }

  *ppSegcsr = pSegcsr;
  return rc;
}

/*
** Free an Fts3MultiSegReader allocated by fts3TermSegReaderCursor().
*/
static void fts3SegReaderCursorFree(Fts3MultiSegReader *pSegcsr){
  sqlite3Fts3SegReaderFinish(pSegcsr);
  sqlite3_free(pSegcsr);
}

/*
** This function retreives the doclist for the specified term (or term
** prefix) from the database. 
** 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 (a bare doclist). 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 */
  Fts3PhraseToken *pTok,          /* Token to query for */
  int iColumn,                    /* Column to query (or -ve for all columns) */
  int isReqPos,                   /* True to include position lists in output */
  int *pnOut,                     /* OUT: Size of buffer at *ppOut */
  char **ppOut                    /* OUT: Malloced result buffer */
){
  int rc;                         /* Return code */
  Fts3MultiSegReader *pSegcsr;   /* Seg-reader cursor for this term */
  TermSelect tsc;                 /* Context object for fts3TermSelectCb() */
  Fts3MultiSegReader *pSegcsr;    /* Seg-reader cursor for this term */
  TermSelect tsc;                 /* Object for pair-wise doclist merging */
  Fts3SegFilter filter;           /* Segment term filter configuration */

  pSegcsr = pTok->pSegcsr;
  memset(&tsc, 0, sizeof(TermSelect));
  tsc.isReqPos = isReqPos;

  filter.flags = FTS3_SEGMENT_IGNORE_EMPTY 
  filter.flags = FTS3_SEGMENT_IGNORE_EMPTY | FTS3_SEGMENT_REQUIRE_POS
        | (pTok->isPrefix ? FTS3_SEGMENT_PREFIX : 0)
        | (isReqPos ? FTS3_SEGMENT_REQUIRE_POS : 0)
        | (iColumn<p->nColumn ? FTS3_SEGMENT_COLUMN_FILTER : 0);
  filter.iCol = iColumn;
  filter.zTerm = pTok->z;
  filter.nTerm = pTok->n;

  rc = sqlite3Fts3SegReaderStart(p, pSegcsr, &filter);
  while( SQLITE_OK==rc
      && SQLITE_ROW==(rc = sqlite3Fts3SegReaderStep(p, pSegcsr)) 
  ){
    rc = fts3TermSelectCb(p, (void *)&tsc, 
        pSegcsr->zTerm, pSegcsr->nTerm, pSegcsr->aDoclist, pSegcsr->nDoclist
    rc = fts3TermSelectMerge(p, &tsc, pSegcsr->aDoclist, pSegcsr->nDoclist);
    );
  }

  if( rc==SQLITE_OK ){
    rc = fts3TermSelectMerge(p, &tsc);
    rc = fts3TermSelectFinishMerge(p, &tsc);
  }
  if( rc==SQLITE_OK ){
    *ppOut = tsc.aaOutput[0];
    *pnOut = tsc.anOutput[0];
  }else{
    int i;
    for(i=0; i<SizeofArray(tsc.aaOutput); i++){

** in buffer aList[], size nList bytes.
**
** If the isPoslist argument is true, then it is assumed that the doclist
** contains a position-list following each docid. Otherwise, it is assumed
** that the doclist is simply a list of docids stored as delta encoded 
** varints.
*/
static int fts3DoclistCountDocids(int isPoslist, char *aList, int nList){
static int fts3DoclistCountDocids(char *aList, int nList){
  int nDoc = 0;                   /* Return value */
  if( aList ){
    char *aEnd = &aList[nList];   /* Pointer to one byte after EOF */
    char *p = aList;              /* Cursor */
    if( !isPoslist ){
      /* The number of docids in the list is the same as the number of 
      ** varints. In FTS3 a varint consists of a single byte with the 0x80 
      ** bit cleared and zero or more bytes with the 0x80 bit set. So to
      ** count the varints in the buffer, just count the number of bytes
      ** with the 0x80 bit clear.  */
      while( p<aEnd ) nDoc += (((*p++)&0x80)==0);
    }else{
      while( p<aEnd ){
        nDoc++;
        while( (*p++)&0x80 );     /* Skip docid varint */
        fts3PoslistCopy(0, &p);   /* Skip over position list */
    while( p<aEnd ){
      nDoc++;
      while( (*p++)&0x80 );     /* Skip docid varint */
      fts3PoslistCopy(0, &p);   /* Skip over position list */
      }
    }
  }

  return nDoc;
}

/*

      pCsr->isEof = 1;
      rc = sqlite3_reset(pCsr->pStmt);
    }else{
      pCsr->iPrevId = sqlite3_column_int64(pCsr->pStmt, 0);
      rc = SQLITE_OK;
    }
  }else{
    rc = sqlite3Fts3EvalNext((Fts3Cursor *)pCursor);
    rc = fts3EvalNext((Fts3Cursor *)pCursor);
  }
  assert( ((Fts3Table *)pCsr->base.pVtab)->pSegments==0 );
  return rc;
}

/*
** This is the xFilter interface for the virtual table.  See

      }
      return rc;
    }

    rc = sqlite3Fts3ReadLock(p);
    if( rc!=SQLITE_OK ) return rc;

    rc = sqlite3Fts3EvalStart(pCsr, pCsr->pExpr, 1);
    rc = fts3EvalStart(pCsr);

    sqlite3Fts3SegmentsClose(p);
    if( rc!=SQLITE_OK ) return rc;
    pCsr->pNextId = pCsr->aDoclist;
    pCsr->iPrevId = 0;
  }

  fts3DbExec(&rc, db,
    "ALTER TABLE %Q.'%q_segdir'   RENAME TO '%q_segdir';",
    p->zDb, p->zName, zName
  );
  return rc;
}

/*
** The xSavepoint() method.
**
** Flush the contents of the pending-terms table to disk.
*/
static int fts3SavepointMethod(sqlite3_vtab *pVtab, int iSavepoint){
  UNUSED_PARAMETER(iSavepoint);
  assert( ((Fts3Table *)pVtab)->inTransaction );
  assert( ((Fts3Table *)pVtab)->mxSavepoint < iSavepoint );
  TESTONLY( ((Fts3Table *)pVtab)->mxSavepoint = iSavepoint );
  return fts3SyncMethod(pVtab);
}

/*
** The xRelease() method.
**
** This is a no-op.
*/
static int fts3ReleaseMethod(sqlite3_vtab *pVtab, int iSavepoint){
  TESTONLY( Fts3Table *p = (Fts3Table*)pVtab );
  UNUSED_PARAMETER(iSavepoint);
  UNUSED_PARAMETER(pVtab);
  assert( p->inTransaction );
  assert( p->mxSavepoint >= iSavepoint );
  TESTONLY( p->mxSavepoint = iSavepoint-1 );
  return SQLITE_OK;
}

/*
** The xRollbackTo() method.
**
** Discard the contents of the pending terms table.
*/
static int fts3RollbackToMethod(sqlite3_vtab *pVtab, int iSavepoint){
  Fts3Table *p = (Fts3Table*)pVtab;
  UNUSED_PARAMETER(iSavepoint);
  assert( p->inTransaction );
  assert( p->mxSavepoint >= iSavepoint );
  TESTONLY( p->mxSavepoint = iSavepoint );
  sqlite3Fts3PendingTermsClear(p);

  assert( rc!=SQLITE_OK );
  if( pHash ){
    sqlite3Fts3HashClear(pHash);
    sqlite3_free(pHash);
  }
  return rc;
}

#if !SQLITE_CORE
int sqlite3_extension_init(
  sqlite3 *db, 
  char **pzErrMsg,
  const sqlite3_api_routines *pApi
){
  SQLITE_EXTENSION_INIT2(pApi)
  return sqlite3Fts3Init(db);
}
#endif


/*
** Allocate an Fts3MultiSegReader for each token in the expression headed
** by pExpr. 
**
** An Fts3SegReader object is a cursor that can seek or scan a range of
** entries within a single segment b-tree. An Fts3MultiSegReader uses multiple
** Fts3SegReader objects internally to provide an interface to seek or scan
** within the union of all segments of a b-tree. Hence the name.
**
** If the allocated Fts3MultiSegReader just seeks to a single entry in a
** segment b-tree (if the term is not a prefix or it is a prefix for which
** there exists prefix b-tree of the right length) then it may be traversed
** and merged incrementally. Otherwise, it has to be merged into an in-memory 
** doclist and then traversed.
*/
static void fts3EvalAllocateReaders(
  Fts3Cursor *pCsr, 
  Fts3Expr *pExpr, 
  Fts3Cursor *pCsr,               /* FTS cursor handle */
  Fts3Expr *pExpr,                /* Allocate readers for this expression */
  int *pnToken,                   /* OUT: Total number of tokens in phrase. */
  int *pnOr,                      /* OUT: Total number of OR nodes in expr. */
  int *pRc
  int *pRc                        /* IN/OUT: Error code */
){
  if( pExpr && SQLITE_OK==*pRc ){
    if( pExpr->eType==FTSQUERY_PHRASE ){
      int i;
      int nToken = pExpr->pPhrase->nToken;
      *pnToken += nToken;
      for(i=0; i<nToken; i++){
        Fts3PhraseToken *pToken = &pExpr->pPhrase->aToken[i];
        int rc = sqlite3Fts3TermSegReaderCursor(pCsr, 
        int rc = fts3TermSegReaderCursor(pCsr, 
            pToken->z, pToken->n, pToken->isPrefix, &pToken->pSegcsr
        );
        if( rc!=SQLITE_OK ){
          *pRc = rc;
          return;
        }
      }
      assert( pExpr->pPhrase->iDoclistToken==0 );
      pExpr->pPhrase->iDoclistToken = -1;
    }else{
      *pnOr += (pExpr->eType==FTSQUERY_OR);
      fts3EvalAllocateReaders(pCsr, pExpr->pLeft, pnToken, pnOr, pRc);
      fts3EvalAllocateReaders(pCsr, pExpr->pRight, pnToken, pnOr, pRc);
    }
  }
}

/*
** Arguments pList/nList contain the doclist for token iToken of phrase p.
** It is merged into the main doclist stored in p->doclist.aAll/nAll.
**
** This function assumes that pList points to a buffer allocated using
** sqlite3_malloc(). This function takes responsibility for eventually
** freeing the buffer.
*/
static void fts3EvalPhraseMergeToken(
  Fts3Table *pTab,
  Fts3Phrase *p,
  int iToken,
  char *pList,
  int nList
  Fts3Table *pTab,                /* FTS Table pointer */
  Fts3Phrase *p,                  /* Phrase to merge pList/nList into */
  int iToken,                     /* Token pList/nList corresponds to */
  char *pList,                    /* Pointer to doclist */
  int nList                       /* Number of bytes in pList */
){
  assert( iToken!=p->iDoclistToken );

  if( pList==0 ){
    sqlite3_free(p->doclist.aAll);
    p->doclist.aAll = 0;
    p->doclist.nAll = 0;

    p->doclist.aAll = pRight;
    p->doclist.nAll = nRight;
  }

  if( iToken>p->iDoclistToken ) p->iDoclistToken = iToken;
}

/*
** Load the doclist for phrase p into p->doclist.aAll/nAll. The loaded doclist
** does not take deferred tokens into account.
**
** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
*/
static int fts3EvalPhraseLoad(
  Fts3Cursor *pCsr, 
  Fts3Phrase *p
  Fts3Cursor *pCsr,               /* FTS Cursor handle */
  Fts3Phrase *p                   /* Phrase object */
){
  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
  int iToken;
  int rc = SQLITE_OK;

  for(iToken=0; rc==SQLITE_OK && iToken<p->nToken; iToken++){
    Fts3PhraseToken *pToken = &p->aToken[iToken];
    assert( pToken->pDeferred==0 || pToken->pSegcsr==0 );

    if( pToken->pSegcsr ){
      int nThis = 0;
      char *pThis = 0;
      rc = fts3TermSelect(pTab, pToken, p->iColumn, 1, &nThis, &pThis);
      rc = fts3TermSelect(pTab, pToken, p->iColumn, &nThis, &pThis);
      if( rc==SQLITE_OK ){
        fts3EvalPhraseMergeToken(pTab, p, iToken, pThis, nThis);
      }
    }
    assert( pToken->pSegcsr==0 );
  }

  return rc;
}

/*
** This function is called on each phrase after the position lists for
** any deferred tokens have been loaded into memory. It updates the phrases
** current position list to include only those positions that are really
** instances of the phrase (after considering deferred tokens). If this
** means that the phrase does not appear in the current row, doclist.pList
** and doclist.nList are both zeroed.
**
** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
*/
static int fts3EvalDeferredPhrase(Fts3Cursor *pCsr, Fts3Phrase *pPhrase){
  int iToken;
  int rc = SQLITE_OK;
  int iToken;                     /* Used to iterate through phrase tokens */
  int rc = SQLITE_OK;             /* Return code */

  int nMaxUndeferred = pPhrase->iDoclistToken;
  char *aPoslist = 0;
  int nPoslist = 0;
  int iPrev = -1;
  char *aPoslist = 0;             /* Position list for deferred tokens */
  int nPoslist = 0;               /* Number of bytes in aPoslist */
  int iPrev = -1;                 /* Token number of previous deferred token */

  assert( pPhrase->doclist.bFreeList==0 );

  for(iToken=0; rc==SQLITE_OK && iToken<pPhrase->nToken; iToken++){
    Fts3PhraseToken *pToken = &pPhrase->aToken[iToken];
    Fts3DeferredToken *pDeferred = pToken->pDeferred;

        }
      }
      iPrev = iToken;
    }
  }

  if( iPrev>=0 ){
    int nMaxUndeferred = pPhrase->iDoclistToken;
    if( nMaxUndeferred<0 ){
      pPhrase->doclist.pList = aPoslist;
      pPhrase->doclist.nList = nPoslist;
      pPhrase->doclist.iDocid = pCsr->iPrevId;
      pPhrase->doclist.bFreeList = 1;
    }else{
      int nDistance;

}

/*
** This function is called for each Fts3Phrase in a full-text query 
** expression to initialize the mechanism for returning rows. Once this
** function has been called successfully on an Fts3Phrase, it may be
** used with fts3EvalPhraseNext() to iterate through the matching docids.
**
** If parameter bOptOk is true, then the phrase may (or may not) use the
** incremental loading strategy. Otherwise, the entire doclist is loaded into
** memory within this call.
**
** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
*/
static int fts3EvalPhraseStart(Fts3Cursor *pCsr, int bOptOk, Fts3Phrase *p){
  int rc;
  int rc;                         /* Error code */
  Fts3PhraseToken *pFirst = &p->aToken[0];
  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;

  if( pCsr->bDesc==pTab->bDescIdx 
   && bOptOk==1 
   && p->nToken==1 
   && pFirst->pSegcsr 

  assert( rc!=SQLITE_OK || p->nToken<1 || p->aToken[0].pSegcsr==0 || p->bIncr );
  return rc;
}

/*
** This function is used to iterate backwards (from the end to start) 
** through doclists.
** through doclists. It is used by this module to iterate through phrase
** doclists in reverse and by the fts3_write.c module to iterate through
** pending-terms lists when writing to databases with "order=desc".
**
** The doclist may be sorted in ascending (parameter bDescIdx==0) or 
** descending (parameter bDescIdx==1) order of docid. Regardless, this
** function iterates from the end of the doclist to the beginning.
*/
void sqlite3Fts3DoclistPrev(
  int bDescIdx,                   /* True if the doclist is desc */
  char *aDoclist,                 /* Pointer to entire doclist */
  int nDoclist,                   /* Length of aDoclist in bytes */
  char **ppIter,                  /* IN/OUT: Iterator pointer */
  sqlite3_int64 *piDocid,         /* IN/OUT: Docid pointer */

** SQLITE_OK.
**
** If there is no "next" entry and no error occurs, then *pbEof is set to
** 1 before returning. Otherwise, if no error occurs and the iterator is
** successfully advanced, *pbEof is set to 0.
*/
static int fts3EvalPhraseNext(
  Fts3Cursor *pCsr, 
  Fts3Phrase *p, 
  u8 *pbEof
  Fts3Cursor *pCsr,               /* FTS Cursor handle */
  Fts3Phrase *p,                  /* Phrase object to advance to next docid */
  u8 *pbEof                       /* OUT: Set to 1 if EOF */
){
  int rc = SQLITE_OK;
  Fts3Doclist *pDL = &p->doclist;
  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;

  if( p->bIncr ){
    assert( p->nToken==1 );

      }
      pDL->pList = pIter;
      fts3PoslistCopy(0, &pIter);
      pDL->nList = (pIter - pDL->pList);

      /* pIter now points just past the 0x00 that terminates the position-
      ** list for document pDL->iDocid. However, if this position-list was
      ** edited in place by fts3EvalNearTrim2(), then pIter may not actually
      ** edited in place by fts3EvalNearTrim(), then pIter may not actually
      ** point to the start of the next docid value. The following line deals
      ** with this case by advancing pIter past the zero-padding added by
      ** fts3EvalNearTrim2().  */
      ** fts3EvalNearTrim().  */
      while( pIter<pEnd && *pIter==0 ) pIter++;

      pDL->pNextDocid = pIter;
      assert( pIter>=&pDL->aAll[pDL->nAll] || *pIter );
      *pbEof = 0;
    }
  }

  return rc;
}

/*
**
** If *pRc is not SQLITE_OK when this function is called, it is a no-op.
** Otherwise, fts3EvalPhraseStart() is called on all phrases within the
** expression. Also the Fts3Expr.bDeferred variable is set to true for any
** expressions for which all descendent tokens are deferred.
**
** If parameter bOptOk is zero, then it is guaranteed that the
** Fts3Phrase.doclist.aAll/nAll variables contain the entire doclist for
** each phrase in the expression (subject to deferred token processing).
** Or, if bOptOk is non-zero, then one or more tokens within the expression
** may be loaded incrementally, meaning doclist.aAll/nAll is not available.
**
** If an error occurs within this function, *pRc is set to an SQLite error
** code before returning.
*/
static void fts3EvalStartReaders(
  Fts3Cursor *pCsr, 
  Fts3Expr *pExpr, 
  int bOptOk,
  int *pRc
  Fts3Cursor *pCsr,               /* FTS Cursor handle */
  Fts3Expr *pExpr,                /* Expression to initialize phrases in */
  int bOptOk,                     /* True to enable incremental loading */
  int *pRc                        /* IN/OUT: Error code */
){
  if( pExpr && SQLITE_OK==*pRc ){
    if( pExpr->eType==FTSQUERY_PHRASE ){
      int i;
      int nToken = pExpr->pPhrase->nToken;
      for(i=0; i<nToken; i++){
        if( pExpr->pPhrase->aToken[i].pDeferred==0 ) break;
      }
      pExpr->bDeferred = (i==nToken);
      *pRc = fts3EvalPhraseStart(pCsr, bOptOk, pExpr->pPhrase);
    }else{
      fts3EvalStartReaders(pCsr, pExpr->pLeft, bOptOk, pRc);
      fts3EvalStartReaders(pCsr, pExpr->pRight, bOptOk, pRc);
      pExpr->bDeferred = (pExpr->pLeft->bDeferred && pExpr->pRight->bDeferred);
    }
  }
}

/*
** An array of the following structures is assembled as part of the process
** of selecting tokens to defer before the query starts executing (as part
** of the xFilter() method). There is one element in the array for each
** token in the FTS expression.
**
** Tokens are divided into AND/NEAR clusters. All tokens in a cluster belong
** to phrases that are connected only by AND and NEAR operators (not OR or
** NOT). When determining tokens to defer, each AND/NEAR cluster is considered
** separately. The root of a tokens AND/NEAR cluster is stored in 
** Fts3TokenAndCost.pRoot.
*/
typedef struct Fts3TokenAndCost Fts3TokenAndCost;
struct Fts3TokenAndCost {
  Fts3Phrase *pPhrase;            /* The phrase the token belongs to */
  int iToken;                     /* Position of token in phrase */
  Fts3PhraseToken *pToken;        /* The token itself */
  Fts3Expr *pRoot; 
  int nOvfl;
  Fts3Expr *pRoot;                /* Root of NEAR/AND cluster */
  int nOvfl;                      /* Number of overflow pages to load doclist */
  int iCol;                       /* The column the token must match */
};

/*
** This function is used to populate an allocated Fts3TokenAndCost array.
**
** If *pRc is not SQLITE_OK when this function is called, it is a no-op.
** Otherwise, if an error occurs during execution, *pRc is set to an
** SQLite error code.
*/
static void fts3EvalTokenCosts(
  Fts3Cursor *pCsr, 
  Fts3Expr *pRoot, 
  Fts3Expr *pExpr, 
  Fts3TokenAndCost **ppTC,
  Fts3Expr ***ppOr,
  int *pRc
  Fts3Cursor *pCsr,               /* FTS Cursor handle */
  Fts3Expr *pRoot,                /* Root of current AND/NEAR cluster */
  Fts3Expr *pExpr,                /* Expression to consider */
  Fts3TokenAndCost **ppTC,        /* Write new entries to *(*ppTC)++ */
  Fts3Expr ***ppOr,               /* Write new OR root to *(*ppOr)++ */
  int *pRc                        /* IN/OUT: Error code */
){
  if( *pRc==SQLITE_OK && pExpr ){
    if( pExpr->eType==FTSQUERY_PHRASE ){
      Fts3Phrase *pPhrase = pExpr->pPhrase;
      int i;
      for(i=0; *pRc==SQLITE_OK && i<pPhrase->nToken; i++){
        Fts3TokenAndCost *pTC = (*ppTC)++;

        (*ppOr)++;
      }
      fts3EvalTokenCosts(pCsr, pRoot, pExpr->pRight, ppTC, ppOr, pRc);
    }
  }
}

/*
** Determine the average document (row) size in pages. If successful,
** write this value to *pnPage and return SQLITE_OK. Otherwise, return
** an SQLite error code.
**
** The average document size in pages is calculated by first calculating 
** determining the average size in bytes, B. If B is less than the amount
** of data that will fit on a single leaf page of an intkey table in
** this database, then the average docsize is 1. Otherwise, it is 1 plus
** the number of overflow pages consumed by a record B bytes in size.
*/
static int fts3EvalAverageDocsize(Fts3Cursor *pCsr, int *pnPage){
  if( pCsr->nRowAvg==0 ){
    /* The average document size, which is required to calculate the cost
     ** of each doclist, has not yet been determined. Read the required 
     ** data from the %_stat table to calculate it.
     **
     ** Entry 0 of the %_stat table is a blob containing (nCol+1) FTS3 
     ** varints, where nCol is the number of columns in the FTS3 table.
     ** The first varint is the number of documents currently stored in
     ** the table. The following nCol varints contain the total amount of
     ** data stored in all rows of each column of the table, from left
     ** to right.
     */
    ** of each doclist, has not yet been determined. Read the required 
    ** data from the %_stat table to calculate it.
    **
    ** Entry 0 of the %_stat table is a blob containing (nCol+1) FTS3 
    ** varints, where nCol is the number of columns in the FTS3 table.
    ** The first varint is the number of documents currently stored in
    ** the table. The following nCol varints contain the total amount of
    ** data stored in all rows of each column of the table, from left
    ** to right.
    */
    int rc;
    Fts3Table *p = (Fts3Table*)pCsr->base.pVtab;
    sqlite3_stmt *pStmt;
    sqlite3_int64 nDoc = 0;
    sqlite3_int64 nByte = 0;
    const char *pEnd;
    const char *a;

    if( rc!=SQLITE_OK ) return rc;
  }

  *pnPage = pCsr->nRowAvg;
  return SQLITE_OK;
}

/*
** This function is called to select the tokens (if any) that will be 
** deferred. The array aTC[] has already been populated when this is
** called.
**
** This function is called once for each AND/NEAR cluster in the 
** expression. Each invocation determines which tokens to defer within
** the cluster with root node pRoot. See comments above the definition
** of struct Fts3TokenAndCost for more details.
**
** If no error occurs, SQLITE_OK is returned and sqlite3Fts3DeferToken()
** called on each token to defer. Otherwise, an SQLite error code is
** returned.
*/
static int fts3EvalSelectDeferred(
  Fts3Cursor *pCsr,
  Fts3Expr *pRoot,
  Fts3TokenAndCost *aTC,
  int nTC
  Fts3Cursor *pCsr,               /* FTS Cursor handle */
  Fts3Expr *pRoot,                /* Consider tokens with this root node */
  Fts3TokenAndCost *aTC,          /* Array of expression tokens and costs */
  int nTC                         /* Number of entries in aTC[] */
){
  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
  int nDocSize = 0;
  int nDocSize = 0;               /* Number of pages per doc loaded */
  int nDocEst = 0;
  int rc = SQLITE_OK;
  int rc = SQLITE_OK;             /* Return code */
  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
  int ii;
  int ii;                         /* Iterator variable for various purposes */
  int nOvfl = 0;                  /* Total overflow pages used by doclists */
  int nToken = 0;                 /* Total number of tokens in cluster */

  int nOvfl = 0;
  int nTerm = 0;
  int nMinEst = 0;                /* The minimum count for any phrase so far. */
  int nLoad4 = 1;                 /* (Phrases that will be loaded)^4. */

  /* Count the tokens in this AND/NEAR cluster. If none of the doclists
  ** associated with the tokens spill onto overflow pages, or if there is
  ** only 1 token, exit early. No tokens to defer in this case. */
  for(ii=0; ii<nTC; ii++){
    if( aTC[ii].pRoot==pRoot ){
      nOvfl += aTC[ii].nOvfl;
      nTerm++;
      nToken++;
    }
  }
  if( nOvfl==0 || nTerm<2 ) return SQLITE_OK;
  if( nOvfl==0 || nToken<2 ) return SQLITE_OK;

  /* Obtain the average docsize (in pages). */
  rc = fts3EvalAverageDocsize(pCsr, &nDocSize);
  assert( rc!=SQLITE_OK || nDocSize>0 );


  /* Iterate through all tokens in this AND/NEAR cluster, in ascending order 
  ** of the number of overflow pages that will be loaded by the pager layer 
  ** to retrieve the entire doclist for the token from the full-text index.
  ** Load the doclists for tokens that are either:
  **
  **   a. The cheapest token in the entire query (i.e. the one visited by the
  **      first iteration of this loop), or
  **
  **   b. Part of a multi-token phrase.
  **
  ** After each token doclist is loaded, merge it with the others from the
  ** same phrase and count the number of documents that the merged doclist
  ** contains. Set variable "nMinEst" to the smallest number of documents in 
  ** any phrase doclist for which 1 or more token doclists have been loaded.
  ** Let nOther be the number of other phrases for which it is certain that
  ** one or more tokens will not be deferred.
  **
  ** Then, for each token, defer it if loading the doclist would result in
  ** loading N or more overflow pages into memory, where N is computed as:
  **
  **    (nMinEst + 4^nOther - 1) / (4^nOther)
  */
  for(ii=0; ii<nTerm && rc==SQLITE_OK; ii++){
    int jj;
    Fts3TokenAndCost *pTC = 0;
  for(ii=0; ii<nToken && rc==SQLITE_OK; ii++){
    int iTC;                      /* Used to iterate through aTC[] array. */
    Fts3TokenAndCost *pTC = 0;    /* Set to cheapest remaining token. */

    /* Set pTC to point to the cheapest remaining token. */
    for(jj=0; jj<nTC; jj++){
      if( aTC[jj].pToken && aTC[jj].pRoot==pRoot 
       && (!pTC || aTC[jj].nOvfl<pTC->nOvfl) 
    for(iTC=0; iTC<nTC; iTC++){
      if( aTC[iTC].pToken && aTC[iTC].pRoot==pRoot 
       && (!pTC || aTC[iTC].nOvfl<pTC->nOvfl) 
      ){
        pTC = &aTC[jj];
        pTC = &aTC[iTC];
      }
    }
    assert( pTC );

    /* At this point pTC points to the cheapest remaining token. */
    if( ii==0 ){
      if( pTC->nOvfl ){
    if( ii && pTC->nOvfl>=((nMinEst+(nLoad4/4)-1)/(nLoad4/4))*nDocSize ){
      /* The number of overflow pages to load for this (and therefore all
      ** subsequent) tokens is greater than the estimated number of pages 
      ** that will be loaded if all subsequent tokens are deferred.
      */
      Fts3PhraseToken *pToken = pTC->pToken;
        nDocEst = (pTC->nOvfl * pTab->nPgsz + pTab->nPgsz) / 10;
      }else{
      rc = sqlite3Fts3DeferToken(pCsr, pToken, pTC->iCol);
      fts3SegReaderCursorFree(pToken->pSegcsr);
      pToken->pSegcsr = 0;
    }else{
      nLoad4 = nLoad4*4;
      if( ii==0 || pTC->pPhrase->nToken>1 ){
        /* Either this is the cheapest token in the entire query, or it is
        ** part of a multi-token phrase. Either way, the entire doclist will
        ** (eventually) be loaded into memory. It may as well be now. */
        Fts3PhraseToken *pToken = pTC->pToken;
        int nList = 0;
        char *pList = 0;
        rc = fts3TermSelect(pTab, pToken, pTC->iCol, 1, &nList, &pList);
        rc = fts3TermSelect(pTab, pToken, pTC->iCol, &nList, &pList);
        assert( rc==SQLITE_OK || pList==0 );

        if( rc==SQLITE_OK ){
          nDocEst = fts3DoclistCountDocids(1, pList, nList);
          int nCount;
          fts3EvalPhraseMergeToken(pTab, pTC->pPhrase, pTC->iToken,pList,nList);
          nCount = fts3DoclistCountDocids(
              pTC->pPhrase->doclist.aAll, pTC->pPhrase->doclist.nAll
          );
          if( ii==0 || nCount<nMinEst ) nMinEst = nCount;
        }
      }
    }else{
      if( pTC->nOvfl>=(nDocEst*nDocSize) ){
        Fts3PhraseToken *pToken = pTC->pToken;
        rc = sqlite3Fts3DeferToken(pCsr, pToken, pTC->iCol);
        fts3SegReaderCursorFree(pToken->pSegcsr);
        pToken->pSegcsr = 0;
      }
      nDocEst = 1 + (nDocEst/4);
    }
    pTC->pToken = 0;
  }

  return rc;
}

/*
** This function is called from within the xFilter method. It initializes
** the full-text query currently stored in pCsr->pExpr. To iterate through
** the results of a query, the caller does:
**
**    fts3EvalStart(pCsr);
**    while( 1 ){
**      fts3EvalNext(pCsr);
**      if( pCsr->bEof ) break;
**      ... return row pCsr->iPrevId to the caller ...
**    }
*/
int sqlite3Fts3EvalStart(Fts3Cursor *pCsr, Fts3Expr *pExpr, int bOptOk){
static int fts3EvalStart(Fts3Cursor *pCsr){
  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
  int rc = SQLITE_OK;
  int nToken = 0;
  int nOr = 0;

  /* Allocate a MultiSegReader for each token in the expression. */
  fts3EvalAllocateReaders(pCsr, pExpr, &nToken, &nOr, &rc);
  fts3EvalAllocateReaders(pCsr, pCsr->pExpr, &nToken, &nOr, &rc);

  /* Call fts3EvalPhraseStart() on all phrases in the expression. TODO:
  ** This call will eventually also be responsible for determining which
  ** tokens are 'deferred' until the document text is loaded into memory.
  **
  ** Each token in each phrase is dealt with using one of the following
  ** three strategies:
  **
  **   1. Entire doclist loaded into memory as part of the
  **      fts3EvalStartReaders() call.
  **
  **   2. Doclist loaded into memory incrementally, as part of each
  **      sqlite3Fts3EvalNext() call.
  **
  **   3. Token doclist is never loaded. Instead, documents are loaded into
  **      memory and scanned for the token as part of the sqlite3Fts3EvalNext()
  **      call. This is known as a "deferred" token.
  */

  /* Determine which, if any, tokens in the expression should be deferred. */
  /* If bOptOk is true, check if there are any tokens that should be deferred.
  */
  if( rc==SQLITE_OK && bOptOk && nToken>1 && pTab->bHasStat ){
  if( rc==SQLITE_OK && nToken>1 && pTab->bHasStat ){
    Fts3TokenAndCost *aTC;
    Fts3Expr **apOr;
    aTC = (Fts3TokenAndCost *)sqlite3_malloc(
        sizeof(Fts3TokenAndCost) * nToken
      + sizeof(Fts3Expr *) * nOr * 2
    );
    apOr = (Fts3Expr **)&aTC[nToken];

    if( !aTC ){
      rc = SQLITE_NOMEM;
    }else{
      int ii;
      Fts3TokenAndCost *pTC = aTC;
      Fts3Expr **ppOr = apOr;

      fts3EvalTokenCosts(pCsr, 0, pExpr, &pTC, &ppOr, &rc);
      fts3EvalTokenCosts(pCsr, 0, pCsr->pExpr, &pTC, &ppOr, &rc);
      nToken = pTC-aTC;
      nOr = ppOr-apOr;

      if( rc==SQLITE_OK ){
        rc = fts3EvalSelectDeferred(pCsr, 0, aTC, nToken);
        for(ii=0; rc==SQLITE_OK && ii<nOr; ii++){
          rc = fts3EvalSelectDeferred(pCsr, apOr[ii], aTC, nToken);
        }
      }

      sqlite3_free(aTC);
    }
  }

  fts3EvalStartReaders(pCsr, pExpr, bOptOk, &rc);
  fts3EvalStartReaders(pCsr, pCsr->pExpr, 1, &rc);
  return rc;
}

/*
** Invalidate the current position list for phrase pPhrase.
*/
static void fts3EvalZeroPoslist(Fts3Phrase *pPhrase){
static void fts3EvalInvalidatePoslist(Fts3Phrase *pPhrase){
  if( pPhrase->doclist.bFreeList ){
    sqlite3_free(pPhrase->doclist.pList);
  }
  pPhrase->doclist.pList = 0;
  pPhrase->doclist.nList = 0;
  pPhrase->doclist.bFreeList = 0;
}

/*
** This function is called to edit the position list associated with
** the phrase object passed as the fifth argument according to a NEAR
** condition. For example:
**
**     abc NEAR/5 "def ghi"
**
** Parameter nNear is passed the NEAR distance of the expression (5 in
** the example above). When this function is called, *paPoslist points to
** the position list, and *pnToken is the number of phrase tokens in, the
** phrase on the other side of the NEAR operator to pPhrase. For example,
** if pPhrase refers to the "def ghi" phrase, then *paPoslist points to
** the position list associated with phrase "abc".
**
** All positions in the pPhrase position list that are not sufficiently
** close to a position in the *paPoslist position list are removed. If this
** leaves 0 positions, zero is returned. Otherwise, non-zero.
**
** Before returning, *paPoslist is set to point to the position lsit 
** associated with pPhrase. And *pnToken is set to the number of tokens in
** pPhrase.
*/
static int fts3EvalNearTrim2(
  int nNear,
static int fts3EvalNearTrim(
  int nNear,                      /* NEAR distance. As in "NEAR/nNear". */
  char *aTmp,                     /* Temporary space to use */
  char **paPoslist,               /* IN/OUT: Position list */
  int *pnToken,                   /* IN/OUT: Tokens in phrase of *paPoslist */
  Fts3Phrase *pPhrase             /* The phrase object to trim the doclist of */
){
  int nParam1 = nNear + pPhrase->nToken;
  int nParam2 = nNear + *pnToken;

    *paPoslist = pPhrase->doclist.pList;
    *pnToken = pPhrase->nToken;
  }

  return res;
}

/*
** This function is a no-op if *pRc is other than SQLITE_OK when it is called.
** Otherwise, it advances the expression passed as the second argument to
** point to the next matching row in the database. Expressions iterate through
** matching rows in docid order. Ascending order if Fts3Cursor.bDesc is zero,
** or descending if it is non-zero.
**
** If an error occurs, *pRc is set to an SQLite error code. Otherwise, if
** successful, the following variables in pExpr are set:
**
**   Fts3Expr.bEof                (non-zero if EOF - there is no next row)
**   Fts3Expr.iDocid              (valid if bEof==0. The docid of the next row)
**
** If the expression is of type FTSQUERY_PHRASE, and the expression is not
** at EOF, then the following variables are populated with the position list
** for the phrase for the visited row:
**
**   FTs3Expr.pPhrase->doclist.nList        (length of pList in bytes)
**   FTs3Expr.pPhrase->doclist.pList        (pointer to position list)
**
** It says above that this function advances the expression to the next
** matching row. This is usually true, but there are the following exceptions:
**
**   1. Deferred tokens are not taken into account. If a phrase consists
**      entirely of deferred tokens, it is assumed to match every row in
**      the db. In this case the position-list is not populated at all. 
**
**      Or, if a phrase contains one or more deferred tokens and one or
**      more non-deferred tokens, then the expression is advanced to the 
**      next possible match, considering only non-deferred tokens. In other
**      words, if the phrase is "A B C", and "B" is deferred, the expression
**      is advanced to the next row that contains an instance of "A * C", 
**      where "*" may match any single token. The position list in this case
**      is populated as for "A * C" before returning.
**
**   2. NEAR is treated as AND. If the expression is "x NEAR y", it is 
**      advanced to point to the next row that matches "x AND y".
** 
** See fts3EvalTestDeferredAndNear() for details on testing if a row is
** really a match, taking into account deferred tokens and NEAR operators.
*/
static void fts3EvalNextRow(
  Fts3Cursor *pCsr,               /* FTS Cursor handle */
  Fts3Expr *pExpr,                /* Expr. to advance to next matching row */
  int *pRc                        /* IN/OUT: Error code */
){
  if( *pRc==SQLITE_OK ){
    int bDescDoclist = pCsr->bDesc;         /* Used by DOCID_CMP() macro */
    assert( pExpr->bEof==0 );
    pExpr->bStart = 1;

    switch( pExpr->eType ){
      case FTSQUERY_NEAR:
      case FTSQUERY_AND: {
        Fts3Expr *pLeft = pExpr->pLeft;
        Fts3Expr *pRight = pExpr->pRight;
        assert( !pLeft->bDeferred || !pRight->bDeferred );

        if( pLeft->bDeferred ){
          /* LHS is entirely deferred. So we assume it matches every row.
          ** Advance the RHS iterator to find the next row visited. */
          fts3EvalNextRow(pCsr, pRight, pRc);
          pExpr->iDocid = pRight->iDocid;
          pExpr->bEof = pRight->bEof;
        }else if( pRight->bDeferred ){
          /* RHS is entirely deferred. So we assume it matches every row.
          ** Advance the LHS iterator to find the next row visited. */
          fts3EvalNextRow(pCsr, pLeft, pRc);
          pExpr->iDocid = pLeft->iDocid;
          pExpr->bEof = pLeft->bEof;
        }else{
          /* Neither the RHS or LHS are deferred. */
          fts3EvalNextRow(pCsr, pLeft, pRc);
          fts3EvalNextRow(pCsr, pRight, pRc);
          while( !pLeft->bEof && !pRight->bEof && *pRc==SQLITE_OK ){
            sqlite3_int64 iDiff = DOCID_CMP(pLeft->iDocid, pRight->iDocid);
            if( iDiff==0 ) break;
            if( iDiff<0 ){
              fts3EvalNextRow(pCsr, pLeft, pRc);
            }else{
              fts3EvalNextRow(pCsr, pRight, pRc);
            }
          }
          pExpr->iDocid = pLeft->iDocid;
          pExpr->bEof = (pLeft->bEof || pRight->bEof);
        }
        break;
      }
  
      case FTSQUERY_OR: {
        Fts3Expr *pLeft = pExpr->pLeft;
        Fts3Expr *pRight = pExpr->pRight;
        sqlite3_int64 iCmp = DOCID_CMP(pLeft->iDocid, pRight->iDocid);

        assert( pLeft->bStart || pLeft->iDocid==pRight->iDocid );
        assert( pRight->bStart || pLeft->iDocid==pRight->iDocid );

        if( pRight->bEof || (pLeft->bEof==0 && iCmp<0) ){
          fts3EvalNextRow(pCsr, pLeft, pRc);
        }else if( pLeft->bEof || (pRight->bEof==0 && iCmp>0) ){
          fts3EvalNextRow(pCsr, pRight, pRc);
        }else{
          fts3EvalNextRow(pCsr, pLeft, pRc);
          fts3EvalNextRow(pCsr, pRight, pRc);
        }

        pExpr->bEof = (pLeft->bEof && pRight->bEof);
        iCmp = DOCID_CMP(pLeft->iDocid, pRight->iDocid);
        if( pRight->bEof || (pLeft->bEof==0 &&  iCmp<0) ){
          pExpr->iDocid = pLeft->iDocid;
        }else{
          pExpr->iDocid = pRight->iDocid;
        }

        break;
      }

      case FTSQUERY_NOT: {
        Fts3Expr *pLeft = pExpr->pLeft;
        Fts3Expr *pRight = pExpr->pRight;

        if( pRight->bStart==0 ){
          fts3EvalNextRow(pCsr, pRight, pRc);
          assert( *pRc!=SQLITE_OK || pRight->bStart );
        }

        fts3EvalNextRow(pCsr, pLeft, pRc);
        if( pLeft->bEof==0 ){
          while( !*pRc 
              && !pRight->bEof 
              && DOCID_CMP(pLeft->iDocid, pRight->iDocid)>0 
          ){
            fts3EvalNextRow(pCsr, pRight, pRc);
          }
        }
        pExpr->iDocid = pLeft->iDocid;
        pExpr->bEof = pLeft->bEof;
        break;
      }

      default: {
        Fts3Phrase *pPhrase = pExpr->pPhrase;
        fts3EvalInvalidatePoslist(pPhrase);
        *pRc = fts3EvalPhraseNext(pCsr, pPhrase, &pExpr->bEof);
        pExpr->iDocid = pPhrase->doclist.iDocid;
        break;
      }
    }
  }
}

/*
** If *pRc is not SQLITE_OK, or if pExpr is not the root node of a NEAR
** cluster, then this function returns 1 immediately.
**
** Otherwise, it checks if the current row really does match the NEAR 
** expression, using the data currently stored in the position lists 
** (Fts3Expr->pPhrase.doclist.pList/nList) for each phrase in the expression. 
**
** If the current row is a match, the position list associated with each
** phrase in the NEAR expression is edited in place to contain only those
** phrase instances sufficiently close to their peers to satisfy all NEAR
** constraints. In this case it returns 1. If the NEAR expression does not 
** match the current row, 0 is returned. The position lists may or may not
** be edited if 0 is returned.
*/
static int fts3EvalNearTest(Fts3Expr *pExpr, int *pRc){
  int res = 1;

  /* The following block runs if pExpr is the root of a NEAR query.
  ** For example, the query:
  **
  **         "w" NEAR "x" NEAR "y" NEAR "z"

  **                     |        |
  **                +--NEAR--+   "y"
  **                |        |
  **               "w"      "x"
  **
  ** The right-hand child of a NEAR node is always a phrase. The 
  ** left-hand child may be either a phrase or a NEAR node. There are
  ** no exceptions to this.
  ** no exceptions to this - it's the way the parser in fts3_expr.c works.
  */
  if( *pRc==SQLITE_OK 
   && pExpr->eType==FTSQUERY_NEAR 
   && pExpr->bEof==0
   && (pExpr->pParent==0 || pExpr->pParent->eType!=FTSQUERY_NEAR)
  ){
    Fts3Expr *p; 

    }else{
      char *aPoslist = p->pPhrase->doclist.pList;
      int nToken = p->pPhrase->nToken;

      for(p=p->pParent;res && p && p->eType==FTSQUERY_NEAR; p=p->pParent){
        Fts3Phrase *pPhrase = p->pRight->pPhrase;
        int nNear = p->nNear;
        res = fts3EvalNearTrim2(nNear, aTmp, &aPoslist, &nToken, pPhrase);
        res = fts3EvalNearTrim(nNear, aTmp, &aPoslist, &nToken, pPhrase);
      }
  
      aPoslist = pExpr->pRight->pPhrase->doclist.pList;
      nToken = pExpr->pRight->pPhrase->nToken;
      for(p=pExpr->pLeft; p && res; p=p->pLeft){
        int nNear = p->pParent->nNear;
        Fts3Phrase *pPhrase = (
            p->eType==FTSQUERY_NEAR ? p->pRight->pPhrase : p->pPhrase
        );
        res = fts3EvalNearTrim2(nNear, aTmp, &aPoslist, &nToken, pPhrase);
        res = fts3EvalNearTrim(nNear, aTmp, &aPoslist, &nToken, pPhrase);
      }
    }

    sqlite3_free(aTmp);
  }

  return res;
}

/*
** This macro is used by the fts3EvalNext() function. The two arguments are
** This function is a helper function for fts3EvalTestDeferredAndNear().
** 64-bit docid values. If the current query is "ORDER BY docid ASC", then
** the macro returns (i1 - i2). Or if it is "ORDER BY docid DESC", then
** it returns (i2 - i1). This allows the same code to be used for merging
** Assuming no error occurs or has occurred, It returns non-zero if the
** doclists in ascending or descending order.
*/
#define DOCID_CMP(i1, i2) ((pCsr->bDesc?-1:1) * (i1-i2))

** expression passed as the second argument matches the row that pCsr 
static void fts3EvalNext(
  Fts3Cursor *pCsr, 
  Fts3Expr *pExpr, 
  int *pRc
){
  if( *pRc==SQLITE_OK ){
    assert( pExpr->bEof==0 );
    pExpr->bStart = 1;

** currently points to, or zero if it does not.
    switch( pExpr->eType ){
      case FTSQUERY_NEAR:
      case FTSQUERY_AND: {
        Fts3Expr *pLeft = pExpr->pLeft;
        Fts3Expr *pRight = pExpr->pRight;
        assert( !pLeft->bDeferred || !pRight->bDeferred );
        if( pLeft->bDeferred ){
          fts3EvalNext(pCsr, pRight, pRc);
          pExpr->iDocid = pRight->iDocid;
          pExpr->bEof = pRight->bEof;
        }else if( pRight->bDeferred ){
          fts3EvalNext(pCsr, pLeft, pRc);
          pExpr->iDocid = pLeft->iDocid;
          pExpr->bEof = pLeft->bEof;
        }else{
          fts3EvalNext(pCsr, pLeft, pRc);
          fts3EvalNext(pCsr, pRight, pRc);

**
          while( !pLeft->bEof && !pRight->bEof && *pRc==SQLITE_OK ){
            sqlite3_int64 iDiff = DOCID_CMP(pLeft->iDocid, pRight->iDocid);
            if( iDiff==0 ) break;
            if( iDiff<0 ){
              fts3EvalNext(pCsr, pLeft, pRc);
            }else{
              fts3EvalNext(pCsr, pRight, pRc);
            }
          }

** If *pRc is not SQLITE_OK when this function is called, it is a no-op.
          pExpr->iDocid = pLeft->iDocid;
          pExpr->bEof = (pLeft->bEof || pRight->bEof);
        }
        break;
      }
  
** If an error occurs during execution of this function, *pRc is set to 
      case FTSQUERY_OR: {
        Fts3Expr *pLeft = pExpr->pLeft;
        Fts3Expr *pRight = pExpr->pRight;
        sqlite3_int64 iCmp = DOCID_CMP(pLeft->iDocid, pRight->iDocid);

** the appropriate SQLite error code. In this case the returned value is 
        assert( pLeft->bStart || pLeft->iDocid==pRight->iDocid );
        assert( pRight->bStart || pLeft->iDocid==pRight->iDocid );

** undefined.
        if( pRight->bEof || (pLeft->bEof==0 && iCmp<0) ){
          fts3EvalNext(pCsr, pLeft, pRc);
        }else if( pLeft->bEof || (pRight->bEof==0 && iCmp>0) ){
          fts3EvalNext(pCsr, pRight, pRc);
        }else{
          fts3EvalNext(pCsr, pLeft, pRc);
          fts3EvalNext(pCsr, pRight, pRc);
        }

*/
        pExpr->bEof = (pLeft->bEof && pRight->bEof);
        iCmp = DOCID_CMP(pLeft->iDocid, pRight->iDocid);
        if( pRight->bEof || (pLeft->bEof==0 &&  iCmp<0) ){
          pExpr->iDocid = pLeft->iDocid;
        }else{
          pExpr->iDocid = pRight->iDocid;
        }

static int fts3EvalTestExpr(
        break;
      }

  Fts3Cursor *pCsr,               /* FTS cursor handle */
      case FTSQUERY_NOT: {
        Fts3Expr *pLeft = pExpr->pLeft;
        Fts3Expr *pRight = pExpr->pRight;

  Fts3Expr *pExpr,                /* Expr to test. May or may not be root. */
        if( pRight->bStart==0 ){
          fts3EvalNext(pCsr, pRight, pRc);
          assert( *pRc!=SQLITE_OK || pRight->bStart );
        }

  int *pRc                        /* IN/OUT: Error code */
        fts3EvalNext(pCsr, pLeft, pRc);
        if( pLeft->bEof==0 ){
          while( !*pRc 
              && !pRight->bEof 
              && DOCID_CMP(pLeft->iDocid, pRight->iDocid)>0 
          ){
){
            fts3EvalNext(pCsr, pRight, pRc);
          }
        }
        pExpr->iDocid = pLeft->iDocid;
        pExpr->bEof = pLeft->bEof;
        break;
      }

      default: {
        Fts3Phrase *pPhrase = pExpr->pPhrase;
        fts3EvalZeroPoslist(pPhrase);
        *pRc = fts3EvalPhraseNext(pCsr, pPhrase, &pExpr->bEof);
        pExpr->iDocid = pPhrase->doclist.iDocid;
        break;
      }
    }
  }
}

static int fts3EvalDeferredTest(Fts3Cursor *pCsr, Fts3Expr *pExpr, int *pRc){
  int bHit = 1;
  int bHit = 1;                   /* Return value */
  if( *pRc==SQLITE_OK ){
    switch( pExpr->eType ){
      case FTSQUERY_NEAR:
      case FTSQUERY_AND:
        bHit = (
            fts3EvalDeferredTest(pCsr, pExpr->pLeft, pRc)
         && fts3EvalDeferredTest(pCsr, pExpr->pRight, pRc)
            fts3EvalTestExpr(pCsr, pExpr->pLeft, pRc)
         && fts3EvalTestExpr(pCsr, pExpr->pRight, pRc)
         && fts3EvalNearTest(pExpr, pRc)
        );

        /* If the NEAR expression does not match any rows, zero the doclist for 
        ** all phrases involved in the NEAR. This is because the snippet(),
        ** offsets() and matchinfo() functions are not supposed to recognize 
        ** any instances of phrases that are part of unmatched NEAR queries. 

        if( bHit==0 
         && pExpr->eType==FTSQUERY_NEAR 
         && (pExpr->pParent==0 || pExpr->pParent->eType!=FTSQUERY_NEAR)
        ){
          Fts3Expr *p;
          for(p=pExpr; p->pPhrase==0; p=p->pLeft){
            if( p->pRight->iDocid==pCsr->iPrevId ){
              fts3EvalZeroPoslist(p->pRight->pPhrase);
              fts3EvalInvalidatePoslist(p->pRight->pPhrase);
            }
          }
          if( p->iDocid==pCsr->iPrevId ){
            fts3EvalZeroPoslist(p->pPhrase);
            fts3EvalInvalidatePoslist(p->pPhrase);
          }
        }

        break;

      case FTSQUERY_OR: {
        int bHit1 = fts3EvalDeferredTest(pCsr, pExpr->pLeft, pRc);
        int bHit2 = fts3EvalDeferredTest(pCsr, pExpr->pRight, pRc);
        int bHit1 = fts3EvalTestExpr(pCsr, pExpr->pLeft, pRc);
        int bHit2 = fts3EvalTestExpr(pCsr, pExpr->pRight, pRc);
        bHit = bHit1 || bHit2;
        break;
      }

      case FTSQUERY_NOT:
        bHit = (
            fts3EvalDeferredTest(pCsr, pExpr->pLeft, pRc)
         && !fts3EvalDeferredTest(pCsr, pExpr->pRight, pRc)
            fts3EvalTestExpr(pCsr, pExpr->pLeft, pRc)
         && !fts3EvalTestExpr(pCsr, pExpr->pRight, pRc)
        );
        break;

      default: {
        if( pCsr->pDeferred 
         && (pExpr->iDocid==pCsr->iPrevId || pExpr->bDeferred)
        ){
          Fts3Phrase *pPhrase = pExpr->pPhrase;
          assert( pExpr->bDeferred || pPhrase->doclist.bFreeList==0 );
          if( pExpr->bDeferred ){
            fts3EvalZeroPoslist(pPhrase);
            fts3EvalInvalidatePoslist(pPhrase);
          }
          *pRc = fts3EvalDeferredPhrase(pCsr, pPhrase);
          bHit = (pPhrase->doclist.pList!=0);
          pExpr->iDocid = pCsr->iPrevId;
        }else{
          bHit = (pExpr->bEof==0 && pExpr->iDocid==pCsr->iPrevId);
        }
        break;
      }
    }
  }
  return bHit;
}

/*
** This function is called as the second part of each xNext operation when
** iterating through the results of a full-text query. At this point the
** cursor points to a row that matches the query expression, with the
** following caveats:
**
**   * Up until this point, "NEAR" operators in the expression have been
**     treated as "AND".
**
**   * Deferred tokens have not yet been considered.
**
** If *pRc is not SQLITE_OK when this function is called, it immediately
** returns 0. Otherwise, it tests whether or not after considering NEAR
** operators and deferred tokens the current row is still a match for the
** Return 1 if both of the following are true:
** expression. It returns 1 if both of the following are true:
**
**   1. *pRc is SQLITE_OK when this function returns, and
**
**   2. After scanning the current FTS table row for the deferred tokens,
**      it is determined that the row does not match the query.
**      it is determined that the row does *not* match the query.
**
** Or, if no error occurs and it seems the current row does match the FTS
** query, return 0.
*/
static int fts3EvalLoadDeferred(Fts3Cursor *pCsr, int *pRc){
static int fts3EvalTestDeferredAndNear(Fts3Cursor *pCsr, int *pRc){
  int rc = *pRc;
  int bMiss = 0;
  if( rc==SQLITE_OK ){

    /* If there are one or more deferred tokens, load the current row into
    ** memory and scan it to determine the position list for each deferred
    ** token. Then, see if this row is really a match, considering deferred
    ** tokens and NEAR operators (neither of which were taken into account
    ** earlier, by fts3EvalNextRow()). 
    */
    if( pCsr->pDeferred ){
      rc = fts3CursorSeek(0, pCsr);
      if( rc==SQLITE_OK ){
        rc = sqlite3Fts3CacheDeferredDoclists(pCsr);
      }
    }
    bMiss = (0==fts3EvalDeferredTest(pCsr, pCsr->pExpr, &rc));
    bMiss = (0==fts3EvalTestExpr(pCsr, pCsr->pExpr, &rc));

    /* Free the position-lists accumulated for each deferred token above. */
    sqlite3Fts3FreeDeferredDoclists(pCsr);
    *pRc = rc;
  }
  return (rc==SQLITE_OK && bMiss);
}

/*
** Advance to the next document that matches the FTS expression in
** Fts3Cursor.pExpr.
*/
int sqlite3Fts3EvalNext(Fts3Cursor *pCsr){
static int fts3EvalNext(Fts3Cursor *pCsr){
  int rc = SQLITE_OK;             /* Return Code */
  Fts3Expr *pExpr = pCsr->pExpr;
  assert( pCsr->isEof==0 );
  if( pExpr==0 ){
    pCsr->isEof = 1;
  }else{
    do {
      if( pCsr->isRequireSeek==0 ){
        sqlite3_reset(pCsr->pStmt);
      }
      assert( sqlite3_data_count(pCsr->pStmt)==0 );
      fts3EvalNext(pCsr, pExpr, &rc);
      fts3EvalNextRow(pCsr, pExpr, &rc);
      pCsr->isEof = pExpr->bEof;
      pCsr->isRequireSeek = 1;
      pCsr->isMatchinfoNeeded = 1;
      pCsr->iPrevId = pExpr->iDocid;
    }while( pCsr->isEof==0 && fts3EvalLoadDeferred(pCsr, &rc) );
    }while( pCsr->isEof==0 && fts3EvalTestDeferredAndNear(pCsr, &rc) );
  }
  return rc;
}

/*
** Restart interation for expression pExpr so that the next call to
** sqlite3Fts3EvalNext() visits the first row. Do not allow incremental 
** fts3EvalNext() visits the first row. Do not allow incremental 
** loading or merging of phrase doclists for this iteration.
**
** If *pRc is other than SQLITE_OK when this function is called, it is
** a no-op. If an error occurs within this function, *pRc is set to an
** SQLite error code before returning.
*/
static void fts3EvalRestart(
  Fts3Cursor *pCsr,
  Fts3Expr *pExpr,
  int *pRc
){
  if( pExpr && *pRc==SQLITE_OK ){
    Fts3Phrase *pPhrase = pExpr->pPhrase;

    if( pPhrase ){
      fts3EvalZeroPoslist(pPhrase);
      fts3EvalInvalidatePoslist(pPhrase);
      if( pPhrase->bIncr ){
        assert( pPhrase->nToken==1 );
        assert( pPhrase->aToken[0].pSegcsr );
        sqlite3Fts3MsrIncrRestart(pPhrase->aToken[0].pSegcsr);
        *pRc = fts3EvalPhraseStart(pCsr, 0, pPhrase);
      }

      do {
        /* Ensure the %_content statement is reset. */
        if( pCsr->isRequireSeek==0 ) sqlite3_reset(pCsr->pStmt);
        assert( sqlite3_data_count(pCsr->pStmt)==0 );

        /* Advance to the next document */
        fts3EvalNext(pCsr, pRoot, &rc);
        fts3EvalNextRow(pCsr, pRoot, &rc);
        pCsr->isEof = pRoot->bEof;
        pCsr->isRequireSeek = 1;
        pCsr->isMatchinfoNeeded = 1;
        pCsr->iPrevId = pRoot->iDocid;
      }while( pCsr->isEof==0 
           && pRoot->eType==FTSQUERY_NEAR 
           && fts3EvalLoadDeferred(pCsr, &rc) 
           && fts3EvalTestDeferredAndNear(pCsr, &rc) 
      );

      if( rc==SQLITE_OK && pCsr->isEof==0 ){
        fts3EvalUpdateCounts(pRoot);
      }
    }

      ** order. For this reason, even though it seems more defensive, the 
      ** do loop can not be written:
      **
      **   do {...} while( pRoot->iDocid<iDocid && rc==SQLITE_OK );
      */
      fts3EvalRestart(pCsr, pRoot, &rc);
      do {
        fts3EvalNext(pCsr, pRoot, &rc);
        fts3EvalNextRow(pCsr, pRoot, &rc);
        assert( pRoot->bEof==0 );
      }while( pRoot->iDocid!=iDocid && rc==SQLITE_OK );
      fts3EvalLoadDeferred(pCsr, &rc);
      fts3EvalTestDeferredAndNear(pCsr, &rc);
    }
  }
  return rc;
}

/*
** This function is used by the matchinfo() module to query a phrase 

**   * the contents of pPhrase->doclist, and
**   * any Fts3MultiSegReader objects held by phrase tokens.
*/
void sqlite3Fts3EvalPhraseCleanup(Fts3Phrase *pPhrase){
  if( pPhrase ){
    int i;
    sqlite3_free(pPhrase->doclist.aAll);
    fts3EvalZeroPoslist(pPhrase);
    fts3EvalInvalidatePoslist(pPhrase);
    memset(&pPhrase->doclist, 0, sizeof(Fts3Doclist));
    for(i=0; i<pPhrase->nToken; i++){
      fts3SegReaderCursorFree(pPhrase->aToken[i].pSegcsr);
      pPhrase->aToken[i].pSegcsr = 0;
    }
  }
}

#if !SQLITE_CORE
/*
** Initialize API pointer table, if required.
*/
int sqlite3_extension_init(
  sqlite3 *db, 
  char **pzErrMsg,
  const sqlite3_api_routines *pApi
){
  SQLITE_EXTENSION_INIT2(pApi)
  return sqlite3Fts3Init(db);
}
#endif

#endif

  int nTerm,                      /* Size of zTerm in bytes */
  int isPrefix,                   /* True for a prefix search */
  Fts3MultiSegReader **ppSegcsr   /* OUT: Allocated seg-reader cursor */
);

void sqlite3Fts3EvalPhraseCleanup(Fts3Phrase *);

int sqlite3Fts3EvalStart(Fts3Cursor *, Fts3Expr *, int);
int sqlite3Fts3EvalNext(Fts3Cursor *pCsr);

int sqlite3Fts3MsrIncrStart(
    Fts3Table*, Fts3MultiSegReader*, int, const char*, int);
int sqlite3Fts3MsrIncrNext(
    Fts3Table *, Fts3MultiSegReader *, sqlite3_int64 *, char **, int *);
char *sqlite3Fts3EvalPhrasePoslist(Fts3Cursor *, Fts3Expr *, int iCol); 
int sqlite3Fts3MsrOvfl(Fts3Cursor *, Fts3MultiSegReader *, int *);
int sqlite3Fts3MsrIncrRestart(Fts3MultiSegReader *pCsr);

  do_execsql_test $tn$title.4 "
    SELECT docid, mit(matchinfo($tbl, 'x')) FROM $tbl 
    WHERE $tbl MATCH '$match' ORDER BY docid ASC
  " $matchinfo_asc
}

#    fts3_make_deferrable TABLE TOKEN
#    fts3_make_deferrable TABLE TOKEN ?NROW?
#
proc fts3_make_deferrable {tbl token} {
proc fts3_make_deferrable {tbl token {nRow 0}} {

  set stmt [sqlite3_prepare db "SELECT * FROM $tbl" -1 dummy]
  set name [sqlite3_column_name $stmt 0]
  sqlite3_finalize $stmt

  if {$nRow==0} {
  set nRow [db one "SELECT count(*) FROM $tbl"]
    set nRow [db one "SELECT count(*) FROM $tbl"]
  }
  set pgsz [db one "PRAGMA page_size"]
  execsql BEGIN
  for {set i 0} {$i < ($nRow * $pgsz * 1.2)/100} {incr i} {
    set doc [string repeat "$token " 100]
    execsql "INSERT INTO $tbl ($name) VALUES(\$doc)"
  }
  execsql "INSERT INTO $tbl ($name) VALUES('aaaaaaa ${token}aaaaa')"

  do_fts3query_test 6.$tn.2 t1 {b:G AND c:I}
  do_fts3query_test 6.$tn.3 t1 {b:G NEAR c:I}
  do_fts3query_test 6.$tn.4 t1 {a:C OR b:G OR c:K OR d:C}
  do_fts3query_test 6.$tn.5 t1 {a:G OR b:G}

  catchsql { COMMIT }
}

foreach {tn create} {
  1    "fts4(x)"
  2    "fts4(x, order=DESC)"
} {
  execsql [subst {
    DROP TABLE IF EXISTS t1;
    CREATE VIRTUAL TABLE t1 USING $create;
  }]

  foreach {x} {
    "F E N O T K X V A X I E X A P G Q V H U"
    "R V A E T C V Q N I E L O N U G J K L U"
    "U Y I G W M V F J L X I D C H F P J Q B"
    "S G D Z X R P G S S Y B K A S G A I L L"
    "L S I C H T Z S R Q P R N K J X L F M J"
    "C C C D P X B Z C M A D A C X S B T X V"
    "W Y J M D R G V R K B X S A W R I T N C"
    "P K L W T M S P O Y Y V V O E H Q A I R"
    "C D Y I C Z F H J C O Y A Q F L S B D K"
    "P G S C Y C Y V I M B D S Z D D Y W I E"
    "Z K Z U E E S F Y X T U A L W O U J C Q"
    "P A T Z S W L P L Q V Y Y I P W U X S S"
    "I U I H U O F Z F R H R F T N D X A G M"
    "N A B M S H K X S O Y D T X S B R Y H Z"
    "L U D A S K I L S V Z J P U B E B Y H M"
  } {
    execsql { INSERT INTO t1 VALUES($x) }
  }

  # Add extra documents to the database such that token "B" will be considered
  # deferrable if considering the other tokens means that 2 or fewer documents
  # will be loaded into memory.
  #
  fts3_make_deferrable t1 B 2

  # B is not deferred in either of the first two tests below, since filtering
  # on "M" or "D" returns 10 documents or so. But filtering on "M * D" only
  # returns 2, so B is deferred in this case.
  #
  do_fts3query_test 7.$tn.1             t1 {"M B"}
  do_fts3query_test 7.$tn.2             t1 {"B D"}
  do_fts3query_test 7.$tn.3 -deferred B t1 {"M B D"}
}

set sqlite_fts3_enable_parentheses $sfep
finish_test