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

/* utility functions */


typedef struct StringBuffer {
  int len;      /* length, not including null terminator */
  int alloced;  /* Space allocated for s[] */ 
  char *s;      /* Content of the string */
} StringBuffer;



static void initStringBuffer(StringBuffer *sb){
  sb->len = 0;
  sb->alloced = 100;
  sb->s = malloc(100);
  sb->s[0] = '\0';
}

static void nappend(StringBuffer *sb, const char *zFrom, int nFrom){
  if( sb->len + nFrom >= sb->alloced ){
    sb->alloced = sb->len + nFrom + 100;
    sb->s = realloc(sb->s, sb->alloced+1);
    if( sb->s==0 ){
      initStringBuffer(sb);
      return;
    }
  }
  memcpy(sb->s + sb->len, zFrom, nFrom);
  sb->len += nFrom;
  sb->s[sb->len] = 0;
}
static void append(StringBuffer *sb, const char *zFrom){
  nappend(sb, zFrom, strlen(zFrom));
}

/* Helper functions for certain common memory-allocation idioms:
**
** data_dup() - malloc+memcpy to duplicate a buffer
** data_replace() - realloc+memcpy to dup a buffer over an existing buffer
** data_append() - realloc+memcpy to append data to an existing buffer
** data_append2() - shorthand for calling data_append() twice.

*/
/* TODO(shess) There is a "block of binary data on the heap" construct
** in here which could be shared with (at least) the StringBuffer and
** DocList constructs.


*/
static void data_replace(char **ppTarget, int *pnTarget,
                         const char *pSource, int nSource){
  *ppTarget = realloc(*ppTarget, nSource);
  memcpy(*ppTarget, pSource, nSource);
  *pnTarget = nSource;



}

static void data_dup(char **ppTarget, int *pnTarget,
                     const char *pSource, int nSource){
  *ppTarget = malloc(nSource);
  memcpy(*ppTarget, pSource, nSource);
  *pnTarget = nSource;




}

static void data_append(char **ppTarget, int *pnTarget,
                        const char *pSource, int nSource){
  *ppTarget = realloc(*ppTarget, *pnTarget+nSource);
  memcpy(*ppTarget+*pnTarget, pSource, nSource);
  *pnTarget += nSource;




}

static void data_append2(char **ppTarget, int *pnTarget,
                         const char *pSource1, int nSource1,
                         const char *pSource2, int nSource2){
  *ppTarget = realloc(*ppTarget, *pnTarget+nSource1+nSource2);
  memcpy(*ppTarget+*pnTarget, pSource1, nSource1);
  memcpy(*ppTarget+*pnTarget+nSource1, pSource2, nSource2);
  *pnTarget += nSource1+nSource2;
}


/* 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. */
................................................................................
 sqlite_int64 i;
 int ret = getVarint(p, &i);
 *pi = (int) i;
 assert( *pi==i );
 return ret;
}

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

/*
** By default, only positions and not offsets are stored in the doclists.
** To change this so that offsets are stored too, compile with
**
**          -DDL_DEFAULT=DL_POSITIONS_OFFSETS
**
** If DL_DEFAULT is set to DL_DOCIDS, your table can only be inserted
** into (no deletes or updates).
*/
#ifndef DL_DEFAULT
# define DL_DEFAULT DL_POSITIONS
#endif

typedef struct DocList {
  char *pData;
  int nData;
  DocListType iType;
  int iLastColumn;    /* the last column written */
  int iLastPos;       /* the last position written */
  int iLastOffset;    /* the last start offset written */
} DocList;

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

/* TODO(shess) I think it might be time to refactor the doclist
** manipulation.  Broadly put, there are four fairly discrete clients,
** tokenization, insert-time segment merging, query-time segment
** merging and query-time analysis.  The breakdown I think might be
** reasonable would be:
**
** DocListReader - Wraps const char *pData, int nData.
**   Used to traverse doclists
** DocListWriter - Starts empty, can add complete doclist elements.
**   Used in merging doclists.
** DocBuilder - Used when tokenizing documents.
*/

static void docListCoreInit(DocList *d, DocListType iType,
                            char *pData, int nData){
  d->nData = nData;
  d->pData = pData;
  d->iType = iType;
  d->iLastColumn = 0;
  d->iLastPos = d->iLastOffset = 0;
}

/* Initialize a new DocList pointing to static data.  Don't call
** docListDestroy() to release, just free(d) (if you originally
** malloced d).
*/
static void docListStaticInit(DocList *d, DocListType iType,
                              const char *pData, int nData){
  docListCoreInit(d, iType, (char *)pData, nData);
}

/* Initialize a new DocList to hold a copy of the given data. */
static void docListInit(DocList *d, DocListType iType,
                        const char *pData, int nData){
  char *p = 0;
  if( nData>0 ){
    p = malloc(nData);
    memcpy(p, pData, nData);
  }
  docListCoreInit(d, iType, p, nData);
}

/* Create a new dynamically-allocated DocList. */
static DocList *docListNew(DocListType iType){
  DocList *d = (DocList *) malloc(sizeof(DocList));
  docListInit(d, iType, 0, 0);
  return d;
}

static void docListDestroy(DocList *d){
  free(d->pData);
#ifndef NDEBUG
  memset(d, 0x55, sizeof(*d));
#endif
}

static void docListDelete(DocList *d){
  docListDestroy(d);
  free(d);
}

static char *docListEnd(DocList *d){
  return d->pData + d->nData;
}

/* Append a varint to a DocList's data. */
static void appendVarint(DocList *d, sqlite_int64 i){
  char c[VARINT_MAX];
  int n = putVarint(c, i);
  d->pData = realloc(d->pData, d->nData + n);
  memcpy(d->pData + d->nData, c, n);
  d->nData += n;
}

static void docListAddDocid(DocList *d, sqlite_int64 iDocid){
  appendVarint(d, iDocid);
  if( d->iType>=DL_POSITIONS ){
    appendVarint(d, POS_END);  /* initially empty position list */
    d->iLastColumn = 0;
    d->iLastPos = d->iLastOffset = 0;
  }
}

/* helper function for docListAddPos and docListAddPosOffset */
static void addPos(DocList *d, int iColumn, int iPos){
  assert( d->nData>0 );
  --d->nData;  /* remove previous terminator */
  if( iColumn!=d->iLastColumn ){
    assert( iColumn>d->iLastColumn );
    appendVarint(d, POS_COLUMN);
    appendVarint(d, iColumn);
    d->iLastColumn = iColumn;
    d->iLastPos = d->iLastOffset = 0;
  }
  assert( iPos>=d->iLastPos );
  appendVarint(d, iPos-d->iLastPos+POS_BASE);
  d->iLastPos = iPos;
}

/* Add a position to the last position list in a doclist. */
static void docListAddPos(DocList *d, int iColumn, int iPos){
  assert( d->iType==DL_POSITIONS );
  addPos(d, iColumn, iPos);
  appendVarint(d, POS_END);  /* add new terminator */
}

/*
** Add a position and starting and ending offsets to a doclist.
**
** If the doclist is setup to handle only positions, then insert
** the position only and ignore the offsets.
*/
static void docListAddPosOffset(
  DocList *d,             /* Doclist under construction */
  int iColumn,            /* Column the inserted term is part of */
  int iPos,               /* Position of the inserted term */
  int iStartOffset,       /* Starting offset of inserted term */
  int iEndOffset          /* Ending offset of inserted term */
){
  assert( d->iType>=DL_POSITIONS );
  addPos(d, iColumn, iPos);
  if( d->iType==DL_POSITIONS_OFFSETS ){
    assert( iStartOffset>=d->iLastOffset );
    appendVarint(d, iStartOffset-d->iLastOffset);
    d->iLastOffset = iStartOffset;
    assert( iEndOffset>=iStartOffset );
    appendVarint(d, iEndOffset-iStartOffset);
  }
  appendVarint(d, POS_END);  /* add new terminator */
}

/*
** A DocListReader object is a cursor into a doclist.  Initialize
** the cursor to the beginning of the doclist by calling readerInit().
** Then use routines
**
**      peekDocid()
**      readDocid()
**      readPosition()
**      skipPositionList()
**      and so forth...
**
** to read information out of the doclist.  When we reach the end
** of the doclist, atEnd() returns TRUE.
*/
typedef struct DocListReader {
  DocList *pDoclist;  /* The document list we are stepping through */
  char *p;            /* Pointer to next unread byte in the doclist */
  int iLastColumn;
  int iLastPos;  /* the last position read, or -1 when not in a position list */
} DocListReader;

/*
** Initialize the DocListReader r to point to the beginning of pDoclist.
*/
static void readerInit(DocListReader *r, DocList *pDoclist){
  r->pDoclist = pDoclist;
  if( pDoclist!=NULL ){
    r->p = pDoclist->pData;
  }
  r->iLastColumn = -1;
  r->iLastPos = -1;
}

/*
** Return TRUE if we have reached then end of pReader and there is
** nothing else left to read.
*/
static int atEnd(DocListReader *pReader){
  return pReader->pDoclist==0 || (pReader->p >= docListEnd(pReader->pDoclist));
}

/* Peek at the next docid without advancing the read pointer. 
*/
static sqlite_int64 peekDocid(DocListReader *pReader){
  sqlite_int64 ret;
  assert( !atEnd(pReader) );
  assert( pReader->iLastPos==-1 );
  getVarint(pReader->p, &ret);
  return ret;
}

/* Read the next docid.   See also nextDocid().
*/
static sqlite_int64 readDocid(DocListReader *pReader){
  sqlite_int64 ret;
  assert( !atEnd(pReader) );
  assert( pReader->iLastPos==-1 );
  pReader->p += getVarint(pReader->p, &ret);
  if( pReader->pDoclist->iType>=DL_POSITIONS ){
    pReader->iLastColumn = 0;
    pReader->iLastPos = 0;
  }
  return ret;
}

/* Read the next position and column index from a position list.
 * Returns the position, or -1 at the end of the list. */
static int readPosition(DocListReader *pReader, int *iColumn){
  int i;
  int iType = pReader->pDoclist->iType;

  if( pReader->iLastPos==-1 ){
    return -1;
  }
  assert( !atEnd(pReader) );

  if( iType<DL_POSITIONS ){
    return -1;
  }
  pReader->p += getVarint32(pReader->p, &i);
  if( i==POS_END ){
    pReader->iLastColumn = pReader->iLastPos = -1;
    *iColumn = -1;
    return -1;
  }
  if( i==POS_COLUMN ){
    pReader->p += getVarint32(pReader->p, &pReader->iLastColumn);
    pReader->iLastPos = 0;
    pReader->p += getVarint32(pReader->p, &i);
    assert( i>=POS_BASE );
  }
  pReader->iLastPos += ((int) i)-POS_BASE;
  if( iType>=DL_POSITIONS_OFFSETS ){
    /* Skip over offsets, ignoring them for now. */
    int iStart, iEnd;
    pReader->p += getVarint32(pReader->p, &iStart);
    pReader->p += getVarint32(pReader->p, &iEnd);
  }
  *iColumn = pReader->iLastColumn;
  return pReader->iLastPos;
}

/* Skip past the end of a position list. */
static void skipPositionList(DocListReader *pReader){
  DocList *p = pReader->pDoclist;
  if( p && p->iType>=DL_POSITIONS ){
    int iColumn;
    while( readPosition(pReader, &iColumn)!=-1 ){}
  }
}

/* Skip over a docid, including its position list if the doclist has
 * positions. */
static void skipDocument(DocListReader *pReader){
  readDocid(pReader);
  skipPositionList(pReader);
}

/* Skip past all docids which are less than [iDocid].  Returns 1 if a docid
 * matching [iDocid] was found.  */
static int skipToDocid(DocListReader *pReader, sqlite_int64 iDocid){
  sqlite_int64 d = 0;
  while( !atEnd(pReader) && (d=peekDocid(pReader))<iDocid ){
    skipDocument(pReader);
  }
  return !atEnd(pReader) && d==iDocid;
}

#ifdef SQLITE_DEBUG
/*
** This routine is used for debugging purpose only.
**
** Write the content of a doclist to standard output.
*/
static void printDoclist(DocList *p){
  DocListReader r;
  const char *zSep = "";

  readerInit(&r, p);
  while( !atEnd(&r) ){
    sqlite_int64 docid = readDocid(&r);
    if( docid==0 ){
      skipPositionList(&r);
      continue;
    }
    printf("%s%lld", zSep, docid);
    zSep =  ",";
    if( p->iType>=DL_POSITIONS ){
      int iPos, iCol;
      const char *zDiv = "";
      printf("(");
      while( (iPos = readPosition(&r, &iCol))>=0 ){
        printf("%s%d:%d", zDiv, iCol, iPos);
        zDiv = ":";
      }
      printf(")");
    }
  }
  printf("\n");
  fflush(stdout);
}
#endif /* SQLITE_DEBUG */

/* Trim the given doclist to contain only positions in column
 * [iRestrictColumn]. */
static void docListRestrictColumn(DocList *in, int iRestrictColumn){
  DocListReader r;
  DocList out;

  assert( in->iType>=DL_POSITIONS );
  readerInit(&r, in);
  docListInit(&out, DL_POSITIONS, NULL, 0);

  while( !atEnd(&r) ){
    sqlite_int64 iDocid = readDocid(&r);
    int iPos, iColumn;

    docListAddDocid(&out, iDocid);
    while( (iPos = readPosition(&r, &iColumn)) != -1 ){
      if( iColumn==iRestrictColumn ){
        docListAddPos(&out, iColumn, iPos);
      }
    }
  }

  docListDestroy(in);
  *in = out;
}

/* Trim the given doclist by discarding any docids without any remaining
 * positions. */
static void docListDiscardEmpty(DocList *in) {
  DocListReader r;
  DocList out;

  /* TODO: It would be nice to implement this operation in place; that
   * could save a significant amount of memory in queries with long doclists. */
  assert( in->iType>=DL_POSITIONS );
  readerInit(&r, in);
  docListInit(&out, DL_POSITIONS, NULL, 0);

  while( !atEnd(&r) ){
    sqlite_int64 iDocid = readDocid(&r);
    int match = 0;
    int iPos, iColumn;
    while( (iPos = readPosition(&r, &iColumn)) != -1 ){
      if( !match ){
        docListAddDocid(&out, iDocid);
        match = 1;
      }
      docListAddPos(&out, iColumn, iPos);
    }
  }

  docListDestroy(in);
  *in = out;
}

/* Efficiently merge left and right into out, with duplicated docids
** from right overwriting those in left (left is effectively older
** than right).  The previous code had a memmove() which introduced an
** O(N^2) into merges, while this code should be O(N).
*/
static void docListMerge(DocList *out, DocList *left, DocList *right){
  DocListReader leftReader, rightReader;
  int iData = 0;
#ifndef NDEBUG
  /* Track these to make certain that every byte is processed. */
  int nLeftProcessed = 0, nRightProcessed = 0;
#endif

  assert( left->iType==right->iType );

  /* Handle edge cases. */
  /* TODO(shess) Consider simply forbidding edge cases, in the
  ** interests of saving copies.
  */
  if( left->nData==0 ){
    docListInit(out, right->iType, right->pData, right->nData);
    return;
  }else if(right->nData==0 ){
    docListInit(out, left->iType, left->pData, left->nData);
    return;
  }
  docListInit(out, left->iType, 0, 0);

  /* At this time, the sum of the space of the inputs is a strict
  ** upper bound.  *out can end up smaller if elements of *right
  ** overwrite elements of *left, but never larger.
  */
  out->nData = left->nData+right->nData;
  out->pData = malloc(out->nData);

  readerInit(&leftReader, left);
  readerInit(&rightReader, right);

  while( !atEnd(&leftReader) && !atEnd(&rightReader) ){
    sqlite_int64 iLeftDocid = peekDocid(&leftReader);
    sqlite_int64 iRightDocid = peekDocid(&rightReader);
    const char *pStart, *pEnd;

    if( iLeftDocid<iRightDocid ){
      /* Copy from *left where less than iRightDocid. */
      pStart = leftReader.p;
      skipToDocid(&leftReader, iRightDocid);
      pEnd = leftReader.p;
#ifndef NDEBUG
      nLeftProcessed += pEnd-pStart;
#endif
    }else{
      /* Copy from *right where less than iLeftDocid, plus the element
      ** matching iLeftDocid, if present.  Also drop the matching
      ** element from *left.
      */
      pStart = rightReader.p;
      if( skipToDocid(&rightReader, iLeftDocid) ){
#ifndef NDEBUG
        const char *pLeftStart = leftReader.p;
#endif
        skipDocument(&leftReader);
        skipDocument(&rightReader);
#ifndef NDEBUG
        nLeftProcessed += leftReader.p-pLeftStart;
#endif
      }
      pEnd = rightReader.p;
#ifndef NDEBUG
      nRightProcessed += pEnd-pStart;
#endif
    }
    assert( pEnd>pStart );
    assert( iData+pEnd-pStart<=out->nData );
    memcpy(out->pData+iData, pStart, pEnd-pStart);
    iData += pEnd-pStart;
  }

  if( !atEnd(&leftReader) ){
    int n = left->nData-(leftReader.p-left->pData);
    assert( atEnd(&rightReader) );
    memcpy(out->pData+iData, leftReader.p, n);
    iData += n;
#ifndef NDEBUG
    nLeftProcessed += n;
#endif
  }else if( !atEnd(&rightReader) ){
    int n = right->nData-(rightReader.p-right->pData);
    memcpy(out->pData+iData, rightReader.p, n);
    iData += n;
#ifndef NDEBUG
    nRightProcessed += n;
#endif
  }
  out->nData = iData;
  out->pData = realloc(out->pData, out->nData);

  assert( nLeftProcessed==left->nData );
  assert( nRightProcessed==right->nData );
}

/*
** Read the next docid off of pIn.  Return 0 if we reach the end.
*
* TODO: This assumes that docids are never 0, but they may actually be 0 since
* users can choose docids when inserting into a full-text table.  Fix this.
*/
static sqlite_int64 nextDocid(DocListReader *pIn){
  skipPositionList(pIn);
  return atEnd(pIn) ? 0 : readDocid(pIn);
}

/*
** pLeft and pRight are two DocListReaders that are pointing to
** positions lists of the same document: iDocid. 
**
** If there are no instances in pLeft or pRight where the position
** of pLeft is one less than the position of pRight, then this
** routine adds nothing to pOut.
**
** If there are one or more instances where positions from pLeft
** are exactly one less than positions from pRight, then add a new
** document record to pOut.  If pOut wants to hold positions, then
** include the positions from pRight that are one more than a
** position in pLeft.  In other words:  pRight.iPos==pLeft.iPos+1.
**
** pLeft and pRight are left pointing at the next document record.
*/
static void mergePosList(
  DocListReader *pLeft,    /* Left position list */
  DocListReader *pRight,   /* Right position list */
  sqlite_int64 iDocid,     /* The docid from pLeft and pRight */
  DocList *pOut            /* Write the merged document record here */
){
  int iLeftCol, iLeftPos = readPosition(pLeft, &iLeftCol);
  int iRightCol, iRightPos = readPosition(pRight, &iRightCol);
  int match = 0;

  /* Loop until we've reached the end of both position lists. */
  while( iLeftPos!=-1 && iRightPos!=-1 ){
    if( iLeftCol==iRightCol && iLeftPos+1==iRightPos ){
      if( !match ){
        docListAddDocid(pOut, iDocid);
        match = 1;
      }
      if( pOut->iType>=DL_POSITIONS ){
        docListAddPos(pOut, iRightCol, iRightPos);
      }
      iLeftPos = readPosition(pLeft, &iLeftCol);
      iRightPos = readPosition(pRight, &iRightCol);
    }else if( iRightCol<iLeftCol ||
              (iRightCol==iLeftCol && iRightPos<iLeftPos+1) ){
      iRightPos = readPosition(pRight, &iRightCol);
    }else{
      iLeftPos = readPosition(pLeft, &iLeftCol);
    }
  }
  if( iLeftPos>=0 ) skipPositionList(pLeft);
  if( iRightPos>=0 ) skipPositionList(pRight);
}

/* We have two doclists:  pLeft and pRight.










































































































































































































































** Write the phrase intersection of these two doclists into pOut.
**
** A phrase intersection means that two documents only match
** if pLeft.iPos+1==pRight.iPos.
**
** The output pOut may or may not contain positions.  If pOut
** does contain positions, they are the positions of pRight.
*/
static void docListPhraseMerge(
  DocList *pLeft,    /* Doclist resulting from the words on the left */
  DocList *pRight,   /* Doclist for the next word to the right */
  DocList *pOut      /* Write the combined doclist here */
){
  DocListReader left, right;
  sqlite_int64 docidLeft, docidRight;

  readerInit(&left, pLeft);
  readerInit(&right, pRight);
  docidLeft = nextDocid(&left);
  docidRight = nextDocid(&right);

  while( docidLeft>0 && docidRight>0 ){
    if( docidLeft<docidRight ){
      docidLeft = nextDocid(&left);
    }else if( docidRight<docidLeft ){
      docidRight = nextDocid(&right);
    }else{
      mergePosList(&left, &right, docidLeft, pOut);
      docidLeft = nextDocid(&left);
      docidRight = nextDocid(&right);
    }
  }
}

/* We have two doclists:  pLeft and pRight.
** Write the intersection of these two doclists into pOut.
** Only docids are matched.  Position information is ignored.
**
** The output pOut never holds positions.
*/
static void docListAndMerge(
  DocList *pLeft,    /* Doclist resulting from the words on the left */
  DocList *pRight,   /* Doclist for the next word to the right */
  DocList *pOut      /* Write the combined doclist here */
){
  DocListReader left, right;
  sqlite_int64 docidLeft, docidRight;

  assert( pOut->iType<DL_POSITIONS );

  readerInit(&left, pLeft);
  readerInit(&right, pRight);
  docidLeft = nextDocid(&left);
  docidRight = nextDocid(&right);

  while( docidLeft>0 && docidRight>0 ){
    if( docidLeft<docidRight ){
      docidLeft = nextDocid(&left);
    }else if( docidRight<docidLeft ){
      docidRight = nextDocid(&right);
    }else{
      docListAddDocid(pOut, docidLeft);
      docidLeft = nextDocid(&left);
      docidRight = nextDocid(&right);
    }
  }
}

/* We have two doclists:  pLeft and pRight.
** Write the union of these two doclists into pOut.
** Only docids are matched.  Position information is ignored.
**
** The output pOut never holds positions.
*/
static void docListOrMerge(
  DocList *pLeft,    /* Doclist resulting from the words on the left */
  DocList *pRight,   /* Doclist for the next word to the right */
  DocList *pOut      /* Write the combined doclist here */
){
  DocListReader left, right;
  sqlite_int64 docidLeft, docidRight, priorLeft;

  readerInit(&left, pLeft);
  readerInit(&right, pRight);
  docidLeft = nextDocid(&left);
  docidRight = nextDocid(&right);

  while( docidLeft>0 && docidRight>0 ){
    if( docidLeft<=docidRight ){
      docListAddDocid(pOut, docidLeft);
    }else{
      docListAddDocid(pOut, docidRight);
    }
    priorLeft = docidLeft;
    if( docidLeft<=docidRight ){
      docidLeft = nextDocid(&left);
    }
    if( docidRight>0 && docidRight<=priorLeft ){
      docidRight = nextDocid(&right);
    }
  }
  while( docidLeft>0 ){
    docListAddDocid(pOut, docidLeft);
    docidLeft = nextDocid(&left);
  }
  while( docidRight>0 ){
    docListAddDocid(pOut, docidRight);
    docidRight = nextDocid(&right);
  }
}

/* We have two doclists:  pLeft and pRight.
** Write into pOut all documents that occur in pLeft but not
** in pRight.
**
** Only docids are matched.  Position information is ignored.
**
** The output pOut never holds positions.
*/
static void docListExceptMerge(
  DocList *pLeft,    /* Doclist resulting from the words on the left */
  DocList *pRight,   /* Doclist for the next word to the right */
  DocList *pOut      /* Write the combined doclist here */
){
  DocListReader left, right;
  sqlite_int64 docidLeft, docidRight, priorLeft;

  readerInit(&left, pLeft);
  readerInit(&right, pRight);
  docidLeft = nextDocid(&left);
  docidRight = nextDocid(&right);

  while( docidLeft>0 && docidRight>0 ){
    priorLeft = docidLeft;
    if( docidLeft<docidRight ){
      docListAddDocid(pOut, docidLeft);
    }
    if( docidLeft<=docidRight ){
      docidLeft = nextDocid(&left);
    }
    if( docidRight>0 && docidRight<=priorLeft ){
      docidRight = nextDocid(&right);
    }
  }
  while( docidLeft>0 ){
    docListAddDocid(pOut, docidLeft);
    docidLeft = nextDocid(&left);
  }








}

static char *string_dup_n(const char *s, int n){
  char *str = malloc(n + 1);
  memcpy(str, s, n);
  str[n] = '\0';
  return str;
................................................................................
  /* SEGDIR_SPAN */
  "select min(start_block), max(end_block) from %_segdir "
  " where level = ? and start_block <> 0",
  /* SEGDIR_DELETE */ "delete from %_segdir where level = ?",
  /* SEGDIR_SELECT_ALL */ "select root from %_segdir order by level desc, idx",
};

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

/*
** 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.
*/
................................................................................
  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 */
  Query q;                         /* Parsed query string */
  Snippet snippet;                 /* Cached snippet for the current row */
  int iColumn;                     /* Column being searched */
  DocListReader result;  /* used when iCursorType == QUERY_FULLTEXT */ 

} fulltext_cursor;

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

static const sqlite3_module fulltextModule;   /* forward declaration */

/* Append a list of strings separated by commas to a StringBuffer. */
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]);
  }
}

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

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

/* Return a dynamically generated statement of the form
 *   update %_content set [col_0] = ?, [col_1] = ?, ...
 *                    where rowid = ?
 */
static const char *contentUpdateStatement(fulltext_vtab *v){
................................................................................
    if( i>0 ){
      append(&sb, ", ");
    }
    append(&sb, v->azContentColumn[i]);
    append(&sb, " = ?");
  }
  append(&sb, " where rowid = ?");
  return sb.s;
}

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

  initStringBuffer(&schema);
  append(&schema, "CREATE TABLE %_content(");
  appendList(&schema, spec.nColumn, spec.azContentColumn);
  append(&schema, ")");
  rc = sql_exec(db, spec.zName, schema.s);
  free(schema.s);
  if( rc!=SQLITE_OK ) goto out;

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

  rc = sql_exec(db, spec.zName,
                "create table %_segdir("
................................................................................
    struct snippetMatch *pMatch = &p->aMatch[i];
    zBuf[0] = ' ';
    sprintf(&zBuf[cnt>0], "%d %d %d %d", pMatch->iCol,
        pMatch->iTerm, pMatch->iStart, pMatch->nByte);
    append(&sb, zBuf);
    cnt++;
  }
  p->zOffset = sb.s;
  p->nOffset = sb.len;
}

/*
** 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.
**
................................................................................
    if( isspace(zDoc[iBreak+i]) ){
      return iBreak + i + 1;
    }
  }
  return iBreak;
}

/*
** If the StringBuffer does not end in white space, add a single
** space character to the end.
*/
static void appendWhiteSpace(StringBuffer *p){
  if( p->len==0 ) return;
  if( isspace(p->s[p->len-1]) ) return;
  append(p, " ");
}

/*
** Remove white space from teh end of the StringBuffer
*/
static void trimWhiteSpace(StringBuffer *p){
  while( p->len>0 && isspace(p->s[p->len-1]) ){
    p->len--;
  }
}



/*
** 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 */
................................................................................
    tailOffset = iEnd;
  }
  trimWhiteSpace(&sb);
  if( tailEllipsis ){
    appendWhiteSpace(&sb);
    append(&sb, zEllipsis);
  }
  pCursor->snippet.zSnippet = sb.s;
  pCursor->snippet.nSnippet = sb.len;  
}


/*
** 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;
  TRACE(("FTS2 Close %p\n", c));
  sqlite3_finalize(c->pStmt);
  queryClear(&c->q);
  snippetClear(&c->snippet);
  if( c->result.pDoclist!=NULL ){
    docListDelete(c->result.pDoclist);

  }
  free(c);
  return SQLITE_OK;
}

static int fulltextNext(sqlite3_vtab_cursor *pCursor){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  sqlite_int64 iDocid;
  int rc;

  TRACE(("FTS2 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);
................................................................................
        c->eof = 1;
        return rc;
    }
  } else {  /* full-text query */
    rc = sqlite3_reset(c->pStmt);
    if( rc!=SQLITE_OK ) return rc;

    iDocid = nextDocid(&c->result);
    if( iDocid==0 ){
      c->eof = 1;
      return SQLITE_OK;
    }
    rc = sqlite3_bind_int64(c->pStmt, 1, iDocid);

    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;
    }
................................................................................


/* 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, DocList *out);


/* Return a DocList corresponding to the query term *pTerm.  If *pTerm
** is the first term of a phrase query, go ahead and evaluate the phrase
** query and return the doclist for the entire phrase query.
**
** The result is stored in pTerm->doclist.

*/
static int docListOfTerm(
  fulltext_vtab *v,     /* The full text index */
  int iColumn,          /* column to restrict to.  No restrition if >=nColumn */
  QueryTerm *pQTerm,    /* Term we are looking for, or 1st term of a phrase */
  DocList **ppResult    /* Write the result here */
){
  DocList *pLeft, *pRight, *pNew;

  int i, rc;

  pLeft = docListNew(DL_POSITIONS);




  rc = termSelect(v, iColumn, pQTerm->pTerm, pQTerm->nTerm, pLeft);

  if( rc ) return rc;
  for(i=1; i<=pQTerm->nPhrase; i++){
    pRight = docListNew(DL_POSITIONS);

    rc = termSelect(v, iColumn, pQTerm[i].pTerm, pQTerm[i].nTerm, pRight);

    if( rc ){
      docListDelete(pLeft);

      return rc;
    }


    pNew = docListNew(i<pQTerm->nPhrase ? DL_POSITIONS : DL_DOCIDS);
    docListPhraseMerge(pLeft, pRight, pNew);
    docListDelete(pLeft);
    docListDelete(pRight);


    pLeft = pNew;
  }
  *ppResult = pLeft;
  return SQLITE_OK;
}

/* Add a new term pTerm[0..nTerm-1] to the query *q.
*/
static void queryAdd(Query *q, const char *pTerm, int nTerm){
  QueryTerm *t;
................................................................................
** 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[] */
  DocList **pResult,     /* Write the result doclist here */
  Query *pQuery          /* Put parsed query string here */
){
  int i, iNext, rc;
  DocList *pLeft = NULL;
  DocList *pRight, *pNew, *pOr;
  int nNot = 0;
  QueryTerm *aTerm;




  rc = parseQuery(v, zInput, nInput, iColumn, pQuery);
  if( rc!=SQLITE_OK ) return rc;

  /* Merge AND terms. */

  aTerm = pQuery->pTerms;
  for(i = 0; i<pQuery->nTerms; i=iNext){
    if( aTerm[i].isNot ){
      /* Handle all NOT terms in a separate pass */
      nNot++;
      iNext = i + aTerm[i].nPhrase+1;
      continue;
    }
    iNext = i + aTerm[i].nPhrase + 1;
    rc = docListOfTerm(v, aTerm[i].iColumn, &aTerm[i], &pRight);
    if( rc ){

      queryClear(pQuery);
      return rc;
    }
    while( iNext<pQuery->nTerms && aTerm[iNext].isOr ){
      rc = docListOfTerm(v, aTerm[iNext].iColumn, &aTerm[iNext], &pOr);
      iNext += aTerm[iNext].nPhrase + 1;
      if( rc ){


        queryClear(pQuery);
        return rc;
      }
      pNew = docListNew(DL_DOCIDS);
      docListOrMerge(pRight, pOr, pNew);
      docListDelete(pRight);
      docListDelete(pOr);
      pRight = pNew;
    }
    if( pLeft==0 ){
      pLeft = pRight;
    }else{
      pNew = docListNew(DL_DOCIDS);
      docListAndMerge(pLeft, pRight, pNew);
      docListDelete(pRight);
      docListDelete(pLeft);
      pLeft = pNew;
    }
  }

  if( nNot && pLeft==0 ){
    /* We do not yet know how to handle a query of only NOT terms */
    return SQLITE_ERROR;
  }

  /* Do the EXCEPT terms */
  for(i=0; i<pQuery->nTerms;  i += aTerm[i].nPhrase + 1){
    if( !aTerm[i].isNot ) continue;
    rc = docListOfTerm(v, aTerm[i].iColumn, &aTerm[i], &pRight);
    if( rc ){
      queryClear(pQuery);
      docListDelete(pLeft);
      return rc;
    }
    pNew = docListNew(DL_DOCIDS);
    docListExceptMerge(pLeft, pRight, pNew);
    docListDelete(pRight);
    docListDelete(pLeft);
    pLeft = pNew;
  }

  *pResult = pLeft;
  return rc;
}

/*
** This is the xFilter interface for the virtual table.  See
** the virtual table xFilter method documentation for additional
** information.
................................................................................
      rc = sqlite3_bind_int64(c->pStmt, 1, sqlite3_value_int64(argv[0]));
      if( rc!=SQLITE_OK ) goto out;
      break;

    default:   /* full-text search */
    {
      const char *zQuery = (const char *)sqlite3_value_text(argv[0]);
      DocList *pResult;
      assert( idxNum<=QUERY_FULLTEXT+v->nColumn);
      assert( argc==1 );
      queryClear(&c->q);

      rc = fulltextQuery(v, idxNum-QUERY_FULLTEXT, zQuery, -1, &pResult, &c->q);
      if( rc!=SQLITE_OK ) goto out;
      readerInit(&c->result, pResult);



      break;
    }
  }

  rc = fulltextNext(pCursor);

out:
................................................................................
  if( rc!=SQLITE_OK ) return rc;

  pCursor->pTokenizer = pTokenizer;
  while( SQLITE_OK==pTokenizer->pModule->xNext(pCursor,
                                               &pToken, &nTokenBytes,
                                               &iStartOffset, &iEndOffset,
                                               &iPosition) ){
    DocList *p;

    /* Positions can't be negative; we use -1 as a terminator internally. */
    if( iPosition<0 ){
      pTokenizer->pModule->xClose(pCursor);
      return SQLITE_ERROR;
    }

    p = fts2HashFind(terms, pToken, nTokenBytes);
    if( p==NULL ){
      p = docListNew(DL_DEFAULT);
      docListAddDocid(p, iDocid);
      fts2HashInsert(terms, pToken, nTokenBytes, p);
    }
    if( iColumn>=0 ){
      docListAddPosOffset(p, iColumn, iPosition, iStartOffset, iEndOffset);
    }
  }

  /* 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*
................................................................................
# 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 {
  char *pTerm;               /* Leftmost term in block's subtree. */
  int nTerm;

  char *pData;
  int nData;

  struct InteriorBlock *next;
} InteriorBlock;

static InteriorBlock *interiorBlockNew(int iHeight, sqlite_int64 iChildBlock,
                                       const char *pTerm, int nTerm){
  InteriorBlock *block = calloc(1, sizeof(InteriorBlock));
  char c[VARINT_MAX+VARINT_MAX];
  int n;

  data_dup(&block->pTerm, &block->nTerm, pTerm, nTerm);


  n = putVarint(c, iHeight);
  n += putVarint(c+n, iChildBlock);
  data_dup(&block->pData, &block->nData, c, n);


  return block;
}

typedef struct InteriorWriter {
  int iHeight;                   /* from 0 at leaves. */
  InteriorBlock *first, *last;
................................................................................
  int n = putVarint(c, nTerm);

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

  if( pWriter->last->nData+n+nTerm>INTERIOR_MAX ){
    /* Overflow to a new block. */
    pWriter->last->next = interiorBlockNew(pWriter->iHeight, iChildBlock,
                                           pTerm, nTerm);
    pWriter->last = pWriter->last->next;
  }else{
    InteriorBlock *last = pWriter->last;
    data_append2(&last->pData, &last->nData, c, n, pTerm, nTerm);
  }
}

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

  while( block!=NULL ){
    InteriorBlock *b = block;
    block = block->next;
    free(b->pData);
    free(b->pTerm);
    free(b);
  }
#ifndef NDEBUG
  memset(pWriter, 0x55, sizeof(pWriter));
#endif
  return SQLITE_OK;
}
................................................................................
                                  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->nData<ROOT_MAX ){
    *ppRootInfo = block->pData;
    *pnRootInfo = block->nData;
    return SQLITE_OK;
  }

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

  pWriter->parentWriter = malloc(sizeof(*pWriter->parentWriter));
  interiorWriterInit(pWriter->iHeight+1,
                     block->pTerm, block->nTerm,
                     iBlockid, pWriter->parentWriter);

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

    interiorWriterAppend(pWriter->parentWriter,
                         block->pTerm, block->nTerm, iBlockid);
  }

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

................................................................................

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

  char *pTerm;                    /* previous encoded term */
  int nTerm;

  char *pData;                    /* encoding buffer */
  int nData;

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

static void leafWriterInit(int iLevel, int idx, LeafWriter *pWriter){



  memset(pWriter, 0, sizeof(*pWriter));
  pWriter->iLevel = iLevel;
  pWriter->idx = idx;



  /* Start out with a reasonably sized block, though it can grow. */
  pWriter->pData = malloc(LEAF_MAX);

  pWriter->nData = putVarint(pWriter->pData, 0);

}















































/* 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){

  sqlite_int64 iBlockid = 0;
  const char *pStartingTerm;
  int nStartingTerm, rc, n;

  /* Must have the leading varint(0) flag, plus at least some data. */


  assert( pWriter->nData>2 );




  rc = block_insert(v, pWriter->pData, pWriter->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 = getVarint32(pWriter->pData+1, &nStartingTerm);
  pStartingTerm = pWriter->pData+1+n;
  assert( pWriter->nData>1+n+nStartingTerm );

  if( pWriter->has_parent ){
    interiorWriterAppend(&pWriter->parentWriter,
                         pStartingTerm, nStartingTerm, iBlockid);
  }else{
    interiorWriterInit(1, pStartingTerm, nStartingTerm, iBlockid,
                       &pWriter->parentWriter);
................................................................................
  if( pWriter->iEndBlockid==0 ){
    pWriter->iEndBlockid = pWriter->iStartBlockid = iBlockid;
  }else{
    pWriter->iEndBlockid++;
    assert( iBlockid==pWriter->iEndBlockid );
  }







  /* Re-initialize the output buffer. */
  pWriter->nData = putVarint(pWriter->pData, 0);
  pWriter->nTerm = 0;


  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 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->nData<ROOT_MAX ){
    *ppRootInfo = pWriter->pData;
    *pnRootInfo = pWriter->nData;
    *piEndBlockid = 0;
    return SQLITE_OK;
  }

  /* Flush remaining leaf data. */
  if( pWriter->nData>1 ){
    int rc = leafWriterInternalFlush(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
................................................................................
                                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 leafWriterFlush(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;

................................................................................
  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);
  free(pWriter->pTerm);
  free(pWriter->pData);
}

/* Push pTerm[nTerm] along with the doclist data to the leaf layer of
** %_segments.
*/
static int leafWriterStep(fulltext_vtab *v, LeafWriter *pWriter,
                          const char *pTerm, int nTerm, DocList *doclist){
  char c[VARINT_MAX+VARINT_MAX];
  int rc, n;

  /* Flush existing data if this item won't fit well. */
  if( pWriter->nData>1 &&
      (doclist->nData+nTerm>STANDALONE_MIN ||
       pWriter->nData+doclist->nData+nTerm>LEAF_MAX) ){
    rc = leafWriterInternalFlush(v, pWriter);
    if( rc!=SQLITE_OK ) return rc;
  }

  if( pWriter->nTerm==0 ){
    /* Encode the entire leading term as:
    **  varint(nTerm)
    **  char pTerm[nTerm]
    */
    n = putVarint(c, nTerm);
    assert( pWriter->nData==1 );
    data_append2(&pWriter->pData, &pWriter->nData,
                 c, n, pTerm, nTerm);
  }else{
    /* Delta-encode the term as:
    **  varint(nPrefix)
    **  varint(nSuffix)
    **  char pTermSuffix[nSuffix]
    */

    int nPrefix = 0;

    while( nPrefix<nTerm && nPrefix<pWriter->nTerm &&
           pTerm[nPrefix]==pWriter->pTerm[nPrefix] ){
      nPrefix++;
    }

    n = putVarint(c, nPrefix);
    n += putVarint(c+n, nTerm-nPrefix);


    data_append2(&pWriter->pData, &pWriter->nData,
                 c, n, pTerm+nPrefix, nTerm-nPrefix);
  }
  data_replace(&pWriter->pTerm, &pWriter->nTerm, pTerm, nTerm);























  /* Encode the doclist as:
  **  varint(nDoclist)
  **  char pDoclist[nDoclist]
  */
  n = putVarint(c, doclist->nData);
  data_append2(&pWriter->pData, &pWriter->nData,
               c, n, doclist->pData, doclist->nData);

  /* Flush standalone blocks right out */
  if( doclist->nData+nTerm>STANDALONE_MIN ){




















































































    rc = leafWriterInternalFlush(v, pWriter);
    if( rc!=SQLITE_OK ) return rc;
  }





























































  return SQLITE_OK;
}


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

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

static void leafReaderDestroy(LeafReader *pReader){
  free(pReader->pTerm);
#ifndef NDEBUG
  memset(pReader, 0x55, sizeof(pReader));
#endif
}

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

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

/* Access the doclist data for the current term. */
static int leafReaderDataBytes(LeafReader *pReader){
  int nData;
  assert( pReader->nTerm>0 );
  getVarint32(pReader->pData, &nData);
  return nData;
}
static const char *leafReaderData(LeafReader *pReader){
  int n, nData;
  assert( pReader->nTerm>0 );
  n = getVarint32(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' );

  memset(pReader, '\0', sizeof(pReader));

  /* Read the first term, skipping the header byte. */
  n = getVarint32(pData+1, &nTerm);

  data_dup(&pReader->pTerm, &pReader->nTerm, 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;
}

................................................................................
  if( !leafReaderAtEnd(pReader) ){
    /* Construct the new term using a prefix from the old term plus a
    ** suffix from the leaf data.
    */
    n = getVarint32(pReader->pData, &nPrefix);
    n += getVarint32(pReader->pData+n, &nSuffix);
    assert( n+nSuffix<pReader->nData );
    pReader->nTerm = nPrefix;
    data_append(&pReader->pTerm, &pReader->nTerm, pReader->pData+n, nSuffix);

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

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

  c = memcmp(pReader->pTerm, pTerm, n);
  if( c!=0 ) return c;
  return pReader->nTerm - 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. */
  char *pRootData;          /* root data for inline. */
} LeavesReader;

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

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

static void leavesReaderDestroy(LeavesReader *pReader){
  leafReaderDestroy(&pReader->leafReader);
  if( pReader->pRootData!=0 ) free(pReader->pRootData);
#ifndef NDEBUG
  memset(pReader, 0x55, sizeof(pReader));
#endif
}

/* Initialize pReader with the given root data (if iStartBlockid==0
** the leaf data was entirely contained in the root), or from the
................................................................................
                            sqlite_int64 iStartBlockid,
                            sqlite_int64 iEndBlockid,
                            const char *pRootData, int nRootData,
                            LeavesReader *pReader){
  memset(pReader, 0, sizeof(*pReader));
  pReader->idx = idx;


  if( iStartBlockid==0 ){
    /* Entire leaf level fit in root data. */
    int n;
    data_dup(&pReader->pRootData, &n, pRootData, nRootData);

    leafReaderInit(pReader->pRootData, nRootData, &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;
................................................................................
*/
static int leavesReaderStep(fulltext_vtab *v, LeavesReader *pReader){
  assert( !leavesReaderAtEnd(pReader) );
  leafReaderStep(&pReader->leafReader);

  if( leafReaderAtEnd(&pReader->leafReader) ){
    int rc;
    if( pReader->pRootData ){
      pReader->eof = 1;
      return SQLITE_OK;
    }
    rc = sql_step_leaf_statement(v, pReader->idx, &pReader->pStmt);
    if( rc!=SQLITE_ROW ){
      pReader->eof = 1;
      return rc==SQLITE_DONE ? SQLITE_OK : rc;
................................................................................
  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) I have a version of this that merges the doclists
** pairwise, and is thus much faster, but is also more intricate.  So
** I'll throw that in as a standalone change.  N-way merge would be
** even faster.
*/
static int leavesReadersMerge(fulltext_vtab *v,
                              LeavesReader *pReaders, int nReaders,
                              LeafWriter *pWriter){

  const char *pTerm = leavesReaderTerm(pReaders);
  int i, rc, nTerm = leavesReaderTermBytes(pReaders);
  DocList doclist;

  /* No need to merge, insert directly. */
  if( nReaders==1 ){
    docListStaticInit(&doclist, DL_DEFAULT,
                      leavesReaderData(pReaders),
                      leavesReaderDataBytes(pReaders));
  }else{
    docListInit(&doclist, DL_DEFAULT,
                leavesReaderData(pReaders),
                leavesReaderDataBytes(pReaders));

    for(i=1; i<nReaders; i++){
      DocList new, merged;
      docListStaticInit(&new, DL_DEFAULT,
                        leavesReaderData(pReaders+i),
                        leavesReaderDataBytes(pReaders+i));
      docListMerge(&merged, &doclist, &new);
      docListDestroy(&doclist);
      doclist = merged;
    }
  }

  /* Insert the new doclist */
  rc = leafWriterStep(v, pWriter, pTerm, nTerm, &doclist);
  if( nReaders>1 ) docListDestroy(&doclist);
  return rc;
}

/* 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
................................................................................
    }
  }

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

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

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

 err:
................................................................................
}

/* Read pData[nData] as a leaf node, and if the doclist for
** pTerm[nTerm] is present, merge it over *out (any duplicate doclists
** read from pData will overwrite those in *out).
*/
static int loadSegmentLeaf(fulltext_vtab *v, const char *pData, int nData,
                           const char *pTerm, int nTerm, DocList *out){
  LeafReader reader;
  assert( nData>1 );
  assert( *pData=='\0' );

  leafReaderInit(pData, nData, &reader);
  while( !leafReaderAtEnd(&reader) ){
    int c = leafReaderTermCmp(&reader, pTerm, nTerm);
    if( c==0 ){
      DocList new, doclist;






      docListStaticInit(&new, DL_DEFAULT,
                        leafReaderData(&reader), leafReaderDataBytes(&reader));

      docListMerge(&doclist, out, &new);
      docListDestroy(out);
      *out = doclist;

    }
    if( c>=0 ) break;
    leafReaderStep(&reader);
  }
  leafReaderDestroy(&reader);
  return SQLITE_OK;
}
................................................................................

/* Traverse the tree represented by pData[nData] looking for
** pTerm[nTerm], merging its doclist over *out if found (any duplicate
** doclists read from the segment rooted at pData will overwrite those
** in *out).
*/
static int loadSegment(fulltext_vtab *v, const char *pData, int nData,
                       const char *pTerm, int nTerm, DocList *out){
  int rc;
  sqlite3_stmt *s = NULL;

  assert( nData>1 );

  /* Process data as an interior node until we reach a leaf. */
  while( *pData!='\0' ){
................................................................................
  return SQLITE_OK;
}

/* 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, DocList *out){

  DocList doclist;
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  docListInit(&doclist, DL_DEFAULT, 0, 0);

  /* Traverse the segments from oldest to newest so that newer doclist
  ** elements for given docids overwrite older elements.
  */
  while( (rc=sql_step_statement(v, SEGDIR_SELECT_ALL_STMT, &s))==SQLITE_ROW ){
    rc = loadSegment(v, sqlite3_column_blob(s, 0), sqlite3_column_bytes(s, 0),
                     pTerm, nTerm, &doclist);
    if( rc!=SQLITE_OK ) goto err;
  }
  if( rc==SQLITE_DONE ){
    *out = doclist;

    /* 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 ){   /* querying a single column */
      docListRestrictColumn(out, iColumn);
    }
    docListDiscardEmpty(out);
    return SQLITE_OK;
  }

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

/****************************************************************/
/* Used to hold hashtable data for sorting. */
typedef struct TermData {
  const char *pTerm;
  int nTerm;
  DocList *pDoclist;
} 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;
................................................................................
** LeafWriter.
*/
static int writeZeroSegment(fulltext_vtab *v, fts2Hash *pTerms){
  fts2HashElem *e;
  int idx, rc, i, n;
  TermData *pData;
  LeafWriter writer;


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

  n = fts2HashCount(pTerms);
  pData = malloc(n*sizeof(TermData));

  for(i = 0, e = fts2HashFirst(pTerms); e; i++, e = fts2HashNext(e)){
    assert( i<n );
    pData[i].pTerm = fts2HashKey(e);
    pData[i].nTerm = fts2HashKeysize(e);
    pData[i].pDoclist = fts2HashData(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);




  leafWriterInit(0, idx, &writer);

  for(i=0; i<n; i++){




    rc = leafWriterStep(v, &writer,
                        pData[i].pTerm, pData[i].nTerm, pData[i].pDoclist);

    if( rc!=SQLITE_OK ) goto err;
  }
  rc = leafWriterFlush(v, &writer);

 err:
  free(pData);
  leafWriterDestroy(&writer);
  return rc;
}

................................................................................
    rc = index_insert(v, ppArg[1], &ppArg[2], pRowid, &terms);
  }

  if( rc==SQLITE_OK ) rc = writeZeroSegment(v, &terms);

  /* clean up */
  for(e=fts2HashFirst(&terms); e; e=fts2HashNext(e)){
    DocList *p = fts2HashData(e);
    docListDelete(p);
  }
  fts2HashClear(&terms);

  return rc;
}

/*

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

typedef enum DocListType {

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



/*
** By default, only positions and not offsets are stored in the doclists.
** To change this so that offsets are stored too, compile with
























**




**          -DDL_DEFAULT=DL_POSITIONS_OFFSETS
**



** If DL_DEFAULT is set to DL_DOCIDS, your table can only be inserted
** into (no deletes or updates).
*/





#ifndef DL_DEFAULT
# define DL_DEFAULT DL_POSITIONS
#endif







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 */

/* 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. */
................................................................................
 sqlite_int64 i;
 int ret = getVarint(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.
** dataBufferExpand - expand capacity without adding data.
** dataBufferAppend - append data.
** dataBufferAppend2 - append two pieces of data at once.
** dataBufferAppendLenData - append a varint-encoded length plus data.
** 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 : malloc(nCapacity);
}
static void dataBufferReset(DataBuffer *pBuffer){
  pBuffer->nData = 0;
}
static void dataBufferDestroy(DataBuffer *pBuffer){
  if( pBuffer->pData!=NULL ) free(pBuffer->pData);
#ifndef NDEBUG
  memset(pBuffer, 0x55, sizeof(*pBuffer));
#endif
}
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 = 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 dataBufferAppendLenData(DataBuffer *pBuffer,
                                    const char *pSource, int nSource){
  char c[VARINT_MAX];
  int n = putVarint(c, nSource);
  dataBufferAppend2(pBuffer, c, n, pSource, nSource);
}
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 &&
    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 = getVarint(pReader->pData, &iDummy);
  assert( !dlrAtEnd(pReader) );
  return pReader->pData+n;
}
static int dlrPosDataLen(DLReader *pReader){
  sqlite_int64 iDummy;
  int n = getVarint(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 ){
    int iDummy, n = getVarint(pReader->pData, &pReader->iDocid);
    if( pReader->iType>=DL_POSITIONS ){
      assert( n<pReader->nData );
      while( 1 ){
        n += getVarint32(pReader->pData+n, &iDummy);
        assert( n<=pReader->nData );
        if( iDummy==POS_END ) break;
        if( iDummy==POS_COLUMN ){
          n += getVarint32(pReader->pData+n, &iDummy);
          assert( n<pReader->nData );
        }else if( pReader->iType==DL_POSITIONS_OFFSETS ){
          n += getVarint32(pReader->pData+n, &iDummy);
          n += getVarint32(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){
#ifndef NDEBUG
  memset(pReader, 0x55, sizeof(pReader));
#endif
}

#ifndef NDEBUG
/* Verify that the doclist can be validly decoded.  Also returns the
** last docid found because it's convenient in other assertions for
** DLWriter.
*/
static int docListValidate(DocListType iType, const char *pData, int nData,
                           sqlite_int64 *pLastDocid){
  int has_prevDocid = 0;
  sqlite_int64 iPrevDocid;
  assert( pData!=0 );
  assert( nData!=0 );
  while( nData!=0 ){
    int n;
    sqlite_int64 iDocid;
    n = getVarint(pData, &iDocid);
    assert( !has_prevDocid || iPrevDocid<iDocid );
    has_prevDocid = 1;
    iPrevDocid = iDocid;
    if( iType>DL_DOCIDS ){
      int iDummy;
      while( 1 ){
        n += getVarint32(pData+n, &iDummy);
        if( iDummy==POS_END ) break;
        if( iDummy==POS_COLUMN ){
          n += getVarint32(pData+n, &iDummy);
        }else if( iType>DL_POSITIONS ){
          n += getVarint32(pData+n, &iDummy);
          n += getVarint32(pData+n, &iDummy);
        }
        assert( n<=nData );
      }
    }
    assert( n<=nData );
    pData += n;
    nData -= n;
  }
  assert( has_prevDocid );
  if( pLastDocid ) *pLastDocid = iPrevDocid;
  return 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.
** dlwAdd - construct doclist element and append to buffer.
*/
/* TODO(shess) Modify to handle delta-encoding docids.  This should be
** fairly simple.  The changes to dlwAdd() are obvious.  dlwAppend()
** would need to decode the leading docid, rencode as a delta, and
** copy the rest of the data (which would already be delta-encoded).
** Note that this will require a change to pass the trailing docid.
*/
typedef struct DLWriter {
  DocListType iType;
  DataBuffer *b;
#ifndef NDEBUG
  int has_prevDocid;
  sqlite_int64 iPrevDocid;
#endif
} DLWriter;

static void dlwInit(DLWriter *pWriter, DocListType iType, DataBuffer *b){
  pWriter->b = b;
  pWriter->iType = iType;
#ifndef NDEBUG
  pWriter->has_prevDocid = 0;
  pWriter->iPrevDocid = 0;
#endif
}
static void dlwDestroy(DLWriter *pWriter){
#ifndef NDEBUG
  memset(pWriter, 0x55, sizeof(pWriter));
#endif
}
static void dlwAppend(DLWriter *pWriter,
                      const char *pData, int nData){
#ifndef NDEBUG
  sqlite_int64 iDocid;
  int n;
  n = getVarint(pData, &iDocid);
  assert( n<=nData );
  assert( !pWriter->has_prevDocid || pWriter->iPrevDocid<iDocid );
  assert( n<nData || pWriter->iType>DL_DOCIDS );
  assert( docListValidate(pWriter->iType, pData, nData, &iDocid) );
  pWriter->has_prevDocid = 1;
  pWriter->iPrevDocid = iDocid;
#endif
  dataBufferAppend(pWriter->b, pData, nData);
}
static void dlwAdd(DLWriter *pWriter, sqlite_int64 iDocid,
                   const char *pPosList, int nPosList){
  char c[VARINT_MAX];
  int n = putVarint(c, iDocid);

  assert( !pWriter->has_prevDocid || pWriter->iPrevDocid<iDocid );
  assert( pPosList==0 || pWriter->iType>DL_DOCIDS );

  dataBufferAppend(pWriter->b, c, n);

  if( pWriter->iType>DL_DOCIDS ){
    n = putVarint(c, 0);
    if( nPosList>0 ){
      dataBufferAppend2(pWriter->b, pPosList, nPosList, c, n);
    }else{
      dataBufferAppend(pWriter->b, c, n);
    }
  }
#ifndef NDEBUG
  pWriter->has_prevDocid = 1;
  pWriter->iPrevDocid = iDocid;
#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 = getVarint32(pReader->pData, &i);
  if( i==POS_COLUMN ){
    n += getVarint32(pReader->pData+n, &pReader->iColumn);
    pReader->iPosition = 0;
    pReader->iStartOffset = 0;
    n += getVarint32(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 += getVarint32(pReader->pData+n, &i);
    pReader->iStartOffset += i;
    n += getVarint32(pReader->pData+n, &i);
    pReader->iEndOffset = pReader->iStartOffset+i;
  }
  assert( n<=pReader->nData );
  pReader->pData += n;
  pReader->nData -= n;
}

static void plrInit(PLReader *pReader, DocListType iType,
                    const char *pData, int nData){
  pReader->pData = pData;
  pReader->nData = nData;
  pReader->iType = iType;
  pReader->iColumn = 0;
  pReader->iPosition = 0;
  pReader->iStartOffset = 0;
  pReader->iEndOffset = 0;
  plrStep(pReader);
}
static void plrDestroy(PLReader *pReader){
#ifndef NDEBUG
  memset(pReader, 0x55, sizeof(pReader));
#endif
}

/*******************************************************************/
/* PLWriter is used in constructing a document's position list.  As a
** convenience, if iType is DL_DOCIDS, PLWriter becomes a no-op.
**
** plwInit - init for writing a document's poslist.
** plwReset - reset the writer for a new document.
** plwDestroy - clear a writer.
** plwNew - malloc storage and initialize it.
** plwDelete - clear and free storage.
** plwDlwAdd - append the docid and poslist to a doclist writer.
** plwAdd - append position and offset information.
*/
/* TODO(shess) PLWriter is used in two ways.  fulltextUpdate() uses it
** in construction of a new doclist.  docListTrim() and mergePosList()
** use it when trimming.  In the former case, it wants to own the
** DataBuffer, in the latter it's possible it could encode into a
** pre-existing DataBuffer.
*/
typedef struct PLWriter {
  DataBuffer b;

  sqlite_int64 iDocid;
  DocListType iType;
  int iColumn;    /* the last column written */
  int iPos;       /* the last position written */
  int iOffset;    /* the last start offset written */
} PLWriter;

static void plwDlwAdd(PLWriter *pWriter, DLWriter *dlWriter){
  dlwAdd(dlWriter, pWriter->iDocid, pWriter->b.pData, pWriter->b.nData);
}
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;

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

  if( iColumn!=pWriter->iColumn ){
    n += putVarint(c+n, POS_COLUMN);
    n += putVarint(c+n, iColumn);
    pWriter->iColumn = iColumn;
    pWriter->iPos = 0;
    pWriter->iOffset = 0;
  }
  assert( iPos>=pWriter->iPos );
  n += putVarint(c+n, POS_BASE+(iPos-pWriter->iPos));
  pWriter->iPos = iPos;
  if( pWriter->iType==DL_POSITIONS_OFFSETS ){
    assert( iStartOffset>=pWriter->iOffset );
    n += putVarint(c+n, iStartOffset-pWriter->iOffset);
    pWriter->iOffset = iStartOffset;
    assert( iEndOffset>=iStartOffset );
    n += putVarint(c+n, iEndOffset-iStartOffset);
  }
  dataBufferAppend(&pWriter->b, c, n);
}
static void plwReset(PLWriter *pWriter,
                     sqlite_int64 iDocid, DocListType iType){
  dataBufferReset(&pWriter->b);
  pWriter->iDocid = iDocid;
  pWriter->iType = iType;
  pWriter->iColumn = 0;
  pWriter->iPos = 0;
  pWriter->iOffset = 0;
}
static void plwInit(PLWriter *pWriter, sqlite_int64 iDocid, DocListType iType){
  dataBufferInit(&pWriter->b, 0);
  plwReset(pWriter, iDocid, iType);
}
static PLWriter *plwNew(sqlite_int64 iDocid, DocListType iType){
  PLWriter *pWriter = malloc(sizeof(PLWriter));
  plwInit(pWriter, iDocid, iType);
  return pWriter;
}
static void plwDestroy(PLWriter *pWriter){
  dataBufferDestroy(&pWriter->b);
#ifndef NDEBUG
  memset(pWriter, 0x55, sizeof(pWriter));
#endif
}
static void plwDelete(PLWriter *pWriter){
  plwDestroy(pWriter);
  free(pWriter);
}


/* 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 iColimn is -1.  Elements with no
** matching columns are dropped.  The output is an iOutType doclist.
*/
static void docListTrim(DocListType iType, const char *pData, int nData,
                        int iColumn, DocListType iOutType, DataBuffer *out){
  DLReader dlReader;
  DLWriter dlWriter;
  PLWriter plWriter;

  assert( iOutType<=iType );

  dlrInit(&dlReader, iType, pData, nData);
  dlwInit(&dlWriter, iOutType, out);
  plwInit(&plWriter, 0, iOutType);

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

    plrInit(&plReader, dlReader.iType,
            dlrPosData(&dlReader), dlrPosDataLen(&dlReader));
    plwReset(&plWriter, dlrDocid(&dlReader), iOutType);

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

    plrDestroy(&plReader);
    dlrStep(&dlReader);
  }
  plwDestroy(&plWriter);
  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;

  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);
      pStart = dlrDocData(readers[0].pReader);
      nStart = dlrDocDataBytes(readers[0].pReader);
    }
    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);
  dlwDestroy(&writer);
}

/* pLeft and pRight are DLReaders positioned to the same docid.
**
** If there are no instances in pLeft or pRight where the position
** of pLeft is one less than the position of pRight, then this
** routine adds nothing to pOut.
**
** If there are one or more instances where positions from pLeft
** are exactly one less than positions from pRight, then add a new
** document record to pOut.  If pOut wants to hold positions, then
** include the positions from pRight that are one more than a
** position in pLeft.  In other words:  pRight.iPos==pLeft.iPos+1.
*/
static void mergePosList(DLReader *pLeft, DLReader *pRight, DLWriter *pOut){
  PLReader left, right;
  PLWriter writer;
  int match = 0;

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

  plrInit(&left, pLeft->iType, dlrPosData(pLeft), dlrPosDataLen(pLeft));
  plrInit(&right, pRight->iType, dlrPosData(pRight), dlrPosDataLen(pRight));
  plwInit(&writer, dlrDocid(pLeft), pOut->iType);

  while( !plrAtEnd(&left) && !plrAtEnd(&right) ){
    if( plrColumn(&left)<plrColumn(&right) ){
      plrStep(&left);
    }else if( plrColumn(&left)>plrColumn(&right) ){
      plrStep(&right);
    }else if( plrPosition(&left)+1<plrPosition(&right) ){
      plrStep(&left);
    }else if( plrPosition(&left)+1>plrPosition(&right) ){
      plrStep(&right);
    }else{
      match = 1;
      plwAdd(&writer, plrColumn(&right), plrPosition(&right), 0, 0);
      plrStep(&left);
      plrStep(&right);
    }
  }

  /* TODO(shess) We could remember the output position, encode the
  ** docid, then encode the poslist directly into the output.  If no
  ** match, we back out to the stored output position.  This would
  ** also reduce the malloc count.
  */
  if( match ) plwDlwAdd(&writer, pOut);

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

/* We have two doclists with positions:  pLeft and pRight.
** Write the phrase intersection of these two doclists into pOut.
**
** A phrase intersection means that two documents only match
** if pLeft.iPos+1==pRight.iPos.
**
** 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,
  DocListType iType,
  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{
      mergePosList(&left, &right, &writer);
      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), 0, 0);
      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 ){
    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) || dlrDocid(&left)<dlrDocid(&right) ){
      dlwAdd(&writer, dlrDocid(&left), 0, 0);
      dlrStep(&left);
    }else if( dlrAtEnd(&left) || dlrDocid(&right)<dlrDocid(&left) ){
      dlwAdd(&writer, dlrDocid(&right), 0, 0);
      dlrStep(&right);
    }else{
      dlwAdd(&writer, dlrDocid(&left), 0, 0);
      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), 0, 0);
    }
    dlrStep(&left);
  }

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

static char *string_dup_n(const char *s, int n){
  char *str = malloc(n + 1);
  memcpy(str, s, n);
  str[n] = '\0';
  return str;
................................................................................
  /* SEGDIR_SPAN */
  "select min(start_block), max(end_block) from %_segdir "
  " where level = ? and start_block <> 0",
  /* SEGDIR_DELETE */ "delete from %_segdir where level = ?",
  /* SEGDIR_SELECT_ALL */ "select root from %_segdir order by level desc, idx",
};






/*
** 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.
*/
................................................................................
  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 */
  Query q;                         /* Parsed 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 struct fulltext_vtab *cursor_vtab(fulltext_cursor *c){
  return (fulltext_vtab *) c->base.pVtab;
}

static const sqlite3_module fulltextModule;   /* forward declaration */










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

................................................................................
  initStringBuffer(&sb);
  append(&sb, "insert into %_content (rowid, ");
  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
 *   update %_content set [col_0] = ?, [col_1] = ?, ...
 *                    where rowid = ?
 */
static const char *contentUpdateStatement(fulltext_vtab *v){
................................................................................
    if( i>0 ){
      append(&sb, ", ");
    }
    append(&sb, v->azContentColumn[i]);
    append(&sb, " = ?");
  }
  append(&sb, " where rowid = ?");
  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,
................................................................................
  rc = parseSpec(&spec, argc, argv, pzErr);
  if( rc!=SQLITE_OK ) return rc;

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

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

  rc = sql_exec(db, spec.zName,
                "create table %_segdir("
................................................................................
    struct snippetMatch *pMatch = &p->aMatch[i];
    zBuf[0] = ' ';
    sprintf(&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.
**
................................................................................
    if( 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 */
................................................................................
    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;
  TRACE(("FTS2 Close %p\n", c));
  sqlite3_finalize(c->pStmt);
  queryClear(&c->q);
  snippetClear(&c->snippet);
  if( c->result.nData!=0 ){
    dlrDestroy(&c->reader);
    dataBufferDestroy(&c->result);
  }
  free(c);
  return SQLITE_OK;
}

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

  int rc;

  TRACE(("FTS2 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);
................................................................................
        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;
    }
................................................................................


/* 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,
                      DocListType iType, DataBuffer *out);

/* Return a DocList corresponding to the query term *pTerm.  If *pTerm
** is the first term of a phrase query, go ahead and evaluate the phrase
** query and return the doclist for the entire phrase query.
**
** The resulting DL_DOCIDS doclist is stored in pResult, which is
** overwritten.
*/
static int docListOfTerm(
  fulltext_vtab *v,   /* The full text index */
  int iColumn,        /* column to restrict to.  No restriction if >=nColumn */
  QueryTerm *pQTerm,  /* Term we are looking for, or 1st term of a phrase */
  DataBuffer *pResult /* Write the result here */
){

  DataBuffer left, right, new;
  int i, rc;


  /* No phrase search if no position info. */
  assert( pQTerm->nPhrase==0 || DL_DEFAULT!=DL_DOCIDS );

  dataBufferInit(&left, 0);
  rc = termSelect(v, iColumn, pQTerm->pTerm, pQTerm->nTerm,
                  0<pQTerm->nPhrase ? DL_POSITIONS : DL_DOCIDS, &left);
  if( rc ) return rc;
  for(i=1; i<=pQTerm->nPhrase && left.nData>0; i++){

    dataBufferInit(&right, 0);
    rc = termSelect(v, iColumn, pQTerm[i].pTerm, pQTerm[i].nTerm,
                    DL_POSITIONS, &right);
    if( rc ){

      dataBufferDestroy(&left);
      return rc;
    }
    dataBufferInit(&new, 0);
    docListPhraseMerge(left.pData, left.nData, right.pData, right.nData,
                       i<pQTerm->nPhrase ? DL_POSITIONS : DL_DOCIDS, &new);



    dataBufferDestroy(&left);
    dataBufferDestroy(&right);
    left = new;
  }
  *pResult = left;
  return SQLITE_OK;
}

/* Add a new term pTerm[0..nTerm-1] to the query *q.
*/
static void queryAdd(Query *q, const char *pTerm, int nTerm){
  QueryTerm *t;
................................................................................
** 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 */
  Query *pQuery          /* Put parsed query string here */
){
  int i, iNext, rc;
  DataBuffer left, right, or, new;

  int nNot = 0;
  QueryTerm *aTerm;

  /* TODO(shess) I think that the queryClear() calls below are not
  ** necessary, because fulltextClose() already clears the query.
  */
  rc = parseQuery(v, zInput, nInput, iColumn, pQuery);
  if( rc!=SQLITE_OK ) return rc;

  /* Merge AND terms. */
  /* TODO(shess) I think we can early-exit if( i>nNot && left.nData==0 ). */
  aTerm = pQuery->pTerms;
  for(i = 0; i<pQuery->nTerms; i=iNext){
    if( aTerm[i].isNot ){
      /* Handle all NOT terms in a separate pass */
      nNot++;
      iNext = i + aTerm[i].nPhrase+1;
      continue;
    }
    iNext = i + aTerm[i].nPhrase + 1;
    rc = docListOfTerm(v, aTerm[i].iColumn, &aTerm[i], &right);
    if( rc ){
      if( i!=nNot ) dataBufferDestroy(&left);
      queryClear(pQuery);
      return rc;
    }
    while( iNext<pQuery->nTerms && aTerm[iNext].isOr ){
      rc = docListOfTerm(v, aTerm[iNext].iColumn, &aTerm[iNext], &or);
      iNext += aTerm[iNext].nPhrase + 1;
      if( rc ){
        if( i!=nNot ) dataBufferDestroy(&left);
        dataBufferDestroy(&right);
        queryClear(pQuery);
        return rc;
      }
      dataBufferInit(&new, 0);
      docListOrMerge(right.pData, right.nData, or.pData, or.nData, &new);
      dataBufferDestroy(&right);
      dataBufferDestroy(&or);
      right = new;
    }
    if( i==nNot ){           /* first term processed. */
      left = right;
    }else{
      dataBufferInit(&new, 0);
      docListAndMerge(left.pData, left.nData, right.pData, right.nData, &new);
      dataBufferDestroy(&right);
      dataBufferDestroy(&left);
      left = new;
    }
  }

  if( nNot==pQuery->nTerms ){
    /* We do not yet know how to handle a query of only NOT terms */
    return SQLITE_ERROR;
  }

  /* Do the EXCEPT terms */
  for(i=0; i<pQuery->nTerms;  i += aTerm[i].nPhrase + 1){
    if( !aTerm[i].isNot ) continue;
    rc = docListOfTerm(v, aTerm[i].iColumn, &aTerm[i], &right);
    if( rc ){
      queryClear(pQuery);
      dataBufferDestroy(&left);
      return rc;
    }
    dataBufferInit(&new, 0);
    docListExceptMerge(left.pData, left.nData, right.pData, right.nData, &new);
    dataBufferDestroy(&right);
    dataBufferDestroy(&left);
    left = new;
  }

  *pResult = left;
  return rc;
}

/*
** This is the xFilter interface for the virtual table.  See
** the virtual table xFilter method documentation for additional
** information.
................................................................................
      rc = sqlite3_bind_int64(c->pStmt, 1, sqlite3_value_int64(argv[0]));
      if( rc!=SQLITE_OK ) goto out;
      break;

    default:   /* full-text search */
    {
      const char *zQuery = (const char *)sqlite3_value_text(argv[0]);

      assert( idxNum<=QUERY_FULLTEXT+v->nColumn);
      assert( argc==1 );
      queryClear(&c->q);
      dataBufferInit(&c->result, 0);
      rc = fulltextQuery(v, idxNum-QUERY_FULLTEXT, zQuery, -1, &c->result, &c->q);
      if( rc!=SQLITE_OK ) return rc;

      if( c->result.nData!=0 ){
        dlrInit(&c->reader, DL_DOCIDS, c->result.pData, c->result.nData);
      }
      break;
    }
  }

  rc = fulltextNext(pCursor);

out:
................................................................................
  if( rc!=SQLITE_OK ) return rc;

  pCursor->pTokenizer = pTokenizer;
  while( SQLITE_OK==pTokenizer->pModule->xNext(pCursor,
                                               &pToken, &nTokenBytes,
                                               &iStartOffset, &iEndOffset,
                                               &iPosition) ){
    PLWriter *p;

    /* Positions can't be negative; we use -1 as a terminator internally. */
    if( iPosition<0 ){
      pTokenizer->pModule->xClose(pCursor);
      return SQLITE_ERROR;
    }

    p = fts2HashFind(terms, pToken, nTokenBytes);
    if( p==NULL ){
      p = plwNew(iDocid, DL_DEFAULT);

      fts2HashInsert(terms, pToken, nTokenBytes, p);
    }
    if( iColumn>=0 ){
      plwAdd(p, iColumn, iPosition, iStartOffset, iEndOffset);
    }
  }

  /* 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*
................................................................................
# 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 = calloc(1, sizeof(InteriorBlock));
  char c[VARINT_MAX+VARINT_MAX];
  int n;

  dataBufferInit(&block->term, 0);
  dataBufferReplace(&block->term, pTerm, nTerm);

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

  return block;
}

typedef struct InteriorWriter {
  int iHeight;                   /* from 0 at leaves. */
  InteriorBlock *first, *last;
................................................................................
  int n = putVarint(c, nTerm);

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

  if( pWriter->last->data.nData+n+nTerm>INTERIOR_MAX ){
    /* Overflow to a new block. */
    pWriter->last->next = interiorBlockNew(pWriter->iHeight, iChildBlock,
                                           pTerm, nTerm);
    pWriter->last = pWriter->last->next;
  }else{

    dataBufferAppend2(&pWriter->last->data, c, n, pTerm, nTerm);
  }
}

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

  while( block!=NULL ){
    InteriorBlock *b = block;
    block = block->next;
    dataBufferDestroy(&b->term);
    dataBufferDestroy(&b->data);
    free(b);
  }
#ifndef NDEBUG
  memset(pWriter, 0x55, sizeof(pWriter));
#endif
  return SQLITE_OK;
}
................................................................................
                                  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.
  */
  rc = block_insert(v, block->data.pData, block->data.nData, &iBlockid);
  if( rc!=SQLITE_OK ) return rc;
  *piEndBlockid = iBlockid;

  pWriter->parentWriter = 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){
    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);
}

................................................................................

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 */


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

static void leafWriterInit(int iLevel, int idx, LeafWriter *pWriter){
  char c[VARINT_MAX];
  int n;

  memset(pWriter, 0, sizeof(*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);
  n = putVarint(c, 0);
  dataBufferReplace(&pWriter->data, c, n);
}

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

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

  /* Must lead with a varint(0) */
  n = getVarint32(pData, &iDummy);
  assert( iDummy==0 );
  if( nData==n ) return 1;
  pData += n;
  nData -= n;

  /* Leading term length and data must fit in buffer. */
  n = getVarint32(pData, &iDummy);
  assert( n+iDummy<nData );
  pData += n+iDummy;
  nData -= n+iDummy;

  /* Leading term's doclist length and data must fit. */
  n = getVarint32(pData, &iDummy);
  assert( n+iDummy<=nData );
  assert( docListValidate(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 = getVarint32(pData, &iDummy);
    n += getVarint32(pData+n, &iDummy);
    assert( n+iDummy<nData );
    pData += n+iDummy;
    nData -= n+iDummy;

    n = getVarint32(pData, &iDummy);
    assert( n+iDummy<=nData );
    assert( docListValidate(DL_DEFAULT, pData+n, iDummy, NULL) );
    pData += n+iDummy;
    nData -= n+iDummy;
  }
  return 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( leafNodeValidate(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 = getVarint32(pWriter->data.pData+iData+1, &nStartingTerm);
  pStartingTerm = pWriter->data.pData+iData+1+n;
  assert( pWriter->data.nData>iData+1+n+nStartingTerm );

  if( pWriter->has_parent ){
    interiorWriterAppend(&pWriter->parentWriter,
                         pStartingTerm, nStartingTerm, iBlockid);
  }else{
    interiorWriterInit(1, pStartingTerm, nStartingTerm, iBlockid,
                       &pWriter->parentWriter);
................................................................................
  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. */
  pWriter->data.nData = putVarint(pWriter->data.pData, 0);

  dataBufferReset(&pWriter->term);

  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 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>1 ){
    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
................................................................................
                                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;

................................................................................
  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. */
static void leafWriterEncodeTerm(LeafWriter *pWriter,


                                 const char *pTerm, int nTerm){




  if( pWriter->term.nData==0 ){







    /* Encode the entire leading term as:
    **  varint(nTerm)
    **  char pTerm[nTerm]
    */

    assert( pWriter->data.nData==1 );

    dataBufferAppendLenData(&pWriter->data, pTerm, nTerm);
  }else{
    /* Delta-encode the term as:
    **  varint(nPrefix)
    **  varint(nSuffix)
    **  char pTermSuffix[nSuffix]
    */
    char c[VARINT_MAX+VARINT_MAX];
    int n, nPrefix = 0;

    while( nPrefix<nTerm && nPrefix<pWriter->term.nData &&
           pTerm[nPrefix]==pWriter->term.pData[nPrefix] ){
      nPrefix++;
    }

    n = putVarint(c, nPrefix);
    n += putVarint(c+n, nTerm-nPrefix);
    dataBufferAppend2(&pWriter->data, c, n, pTerm+nPrefix, nTerm-nPrefix);
  }

  dataBufferReplace(&pWriter->term, pTerm, nTerm);
}


/* 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.  That implies refactoring
** leafWriterStep() and leafWriterStepMerge() to share more code.
*/
static int leafWriterStep(fulltext_vtab *v, LeafWriter *pWriter,
                          const char *pTerm, int nTerm,
                          const char *pData, int nData){
  int rc;

  /* Flush existing data if this item won't fit well. */
  if( pWriter->data.nData>1 &&
      (nData+nTerm>STANDALONE_MIN ||
       pWriter->data.nData+nData+nTerm>LEAF_MAX) ){
    rc = leafWriterFlush(v, pWriter);
    if( rc!=SQLITE_OK ) return rc;
  }

  leafWriterEncodeTerm(pWriter, pTerm, nTerm);

  /* Encode the doclist as:
  **  varint(nDoclist)
  **  char pDoclist[nDoclist]
  */
  dataBufferAppendLenData(&pWriter->data, pData, nData);



  /* Flush standalone blocks right out */
  if( nData+nTerm>STANDALONE_MIN ){
    rc = leafWriterFlush(v, pWriter);
    if( rc!=SQLITE_OK ) return rc;
  }

  return SQLITE_OK;
}

/* 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 = putVarint(c, 0);
  n += putVarint(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;

  assert( leafNodeValidate(pWriter->data.pData, pWriter->data.nData) );
  leafWriterEncodeTerm(pWriter, pTerm, nTerm);

  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 = putVarint(c, nData);
  dataBufferAppend(&pWriter->data, c, n);

  docListMerge(&pWriter->data, pReaders, nReaders);
  assert( docListValidate(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 = putVarint(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>1 ){
      rc = leafWriterInternalFlush(v, pWriter, 0, iTermData);
      if( rc!=SQLITE_OK ) return rc;
    }

    /* 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. */
    pWriter->data.nData = putVarint(pWriter->data.pData, 0);
    dataBufferReset(&pWriter->term);
    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;

    /* Rebuild header using the current term */
    n = putVarint(pWriter->data.pData, 0);
    n += putVarint(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( leafNodeValidate(pWriter->data.pData, pWriter->data.nData) );

  return SQLITE_OK;
}


/****************************************************************/
/* 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);
#ifndef NDEBUG
  memset(pReader, 0x55, sizeof(pReader));
#endif
}

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 );
  getVarint32(pReader->pData, &nData);
  return nData;
}
static const char *leafReaderData(LeafReader *pReader){
  int n, nData;
  assert( pReader->term.nData>0 );
  n = getVarint32(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' );

  memset(pReader, '\0', sizeof(pReader));

  /* Read the first term, skipping the header byte. */
  n = getVarint32(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;
}

................................................................................
  if( !leafReaderAtEnd(pReader) ){
    /* Construct the new term using a prefix from the old term plus a
    ** suffix from the leaf data.
    */
    n = getVarint32(pReader->pData, &nPrefix);
    n += getVarint32(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. */
static int leafReaderTermCmp(LeafReader *pReader,
                             const char *pTerm, int nTerm){
  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;
  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 int leavesReaderAtEnd(LeavesReader *pReader){
  return pReader->eof;
}

static void leavesReaderDestroy(LeavesReader *pReader){
  leafReaderDestroy(&pReader->leafReader);
  dataBufferDestroy(&pReader->rootData);
#ifndef NDEBUG
  memset(pReader, 0x55, sizeof(pReader));
#endif
}

/* Initialize pReader with the given root data (if iStartBlockid==0
** the leaf data was entirely contained in the root), or from the
................................................................................
                            sqlite_int64 iStartBlockid,
                            sqlite_int64 iEndBlockid,
                            const char *pRootData, int nRootData,
                            LeavesReader *pReader){
  memset(pReader, 0, sizeof(*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;
................................................................................
*/
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 = sql_step_leaf_statement(v, pReader->idx, &pReader->pStmt);
    if( rc!=SQLITE_ROW ){
      pReader->eof = 1;
      return rc==SQLITE_DONE ? SQLITE_OK : rc;
................................................................................
  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
................................................................................
    }
  }

  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:
................................................................................
}

/* Read pData[nData] as a leaf node, and if the doclist for
** pTerm[nTerm] is present, merge it over *out (any duplicate doclists
** read from pData will overwrite those in *out).
*/
static int loadSegmentLeaf(fulltext_vtab *v, const char *pData, int nData,
                           const char *pTerm, int nTerm, DataBuffer *out){
  LeafReader reader;
  assert( nData>1 );
  assert( *pData=='\0' );

  leafReaderInit(pData, nData, &reader);
  while( !leafReaderAtEnd(&reader) ){
    int c = leafReaderTermCmp(&reader, pTerm, nTerm);
    if( c==0 ){
      if( out->nData==0 ){
        dataBufferReplace(out,
                          leafReaderData(&reader), leafReaderDataBytes(&reader));
      }else{
        DLReader readers[2];
        DataBuffer result;
        dlrInit(&readers[0], DL_DEFAULT, out->pData, out->nData);
        dlrInit(&readers[1], DL_DEFAULT,
                leafReaderData(&reader), leafReaderDataBytes(&reader));
        dataBufferInit(&result, out->nData+leafReaderDataBytes(&reader));
        docListMerge(&result, readers, 2);
        dataBufferDestroy(out);
        *out = result;
      }
    }
    if( c>=0 ) break;
    leafReaderStep(&reader);
  }
  leafReaderDestroy(&reader);
  return SQLITE_OK;
}
................................................................................

/* Traverse the tree represented by pData[nData] looking for
** pTerm[nTerm], merging its doclist over *out if found (any duplicate
** doclists read from the segment rooted at pData will overwrite those
** in *out).
*/
static int loadSegment(fulltext_vtab *v, const char *pData, int nData,
                       const char *pTerm, int nTerm, DataBuffer *out){
  int rc;
  sqlite3_stmt *s = NULL;

  assert( nData>1 );

  /* Process data as an interior node until we reach a leaf. */
  while( *pData!='\0' ){
................................................................................
  return SQLITE_OK;
}

/* 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,
                      DocListType iType, DataBuffer *out){
  DataBuffer doclist;
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  dataBufferInit(&doclist, 0);

  /* Traverse the segments from oldest to newest so that newer doclist
  ** elements for given docids overwrite older elements.
  */
  while( (rc=sql_step_statement(v, SEGDIR_SELECT_ALL_STMT, &s))==SQLITE_ROW ){
    rc = loadSegment(v, sqlite3_column_blob(s, 0), sqlite3_column_bytes(s, 0),
                     pTerm, nTerm, &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;
  PLWriter *pWriter;
} 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;
................................................................................
** LeafWriter.
*/
static int writeZeroSegment(fulltext_vtab *v, fts2Hash *pTerms){
  fts2HashElem *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 = fts2HashCount(pTerms);
  pData = malloc(n*sizeof(TermData));

  for(i = 0, e = fts2HashFirst(pTerms); e; i++, e = fts2HashNext(e)){
    assert( i<n );
    pData[i].pTerm = fts2HashKey(e);
    pData[i].nTerm = fts2HashKeysize(e);
    pData[i].pWriter = fts2HashData(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++){
    DLWriter dlw;
    dataBufferReset(&dl);
    dlwInit(&dlw, DL_DEFAULT, &dl);
    plwDlwAdd(pData[i].pWriter, &dlw);
    rc = leafWriterStep(v, &writer,
                        pData[i].pTerm, pData[i].nTerm, dl.pData, dl.nData);
    dlwDestroy(&dlw);
    if( rc!=SQLITE_OK ) goto err;
  }
  rc = leafWriterFinalize(v, &writer);

 err:
  free(pData);
  leafWriterDestroy(&writer);
  return rc;
}

................................................................................
    rc = index_insert(v, ppArg[1], &ppArg[2], pRowid, &terms);
  }

  if( rc==SQLITE_OK ) rc = writeZeroSegment(v, &terms);

  /* clean up */
  for(e=fts2HashFirst(&terms); e; e=fts2HashNext(e)){
    plwDelete(fts2HashData(e));

  }
  fts2HashClear(&terms);

  return rc;
}

/*