typedef struct Fts5Structure Fts5Structure;
typedef struct Fts5StructureLevel Fts5StructureLevel;
typedef struct Fts5StructureSegment Fts5StructureSegment;

struct Fts5Data {
  u8 *p;                          /* Pointer to buffer containing record */
  int n;                          /* Size of record in bytes */
  int nRef;                       /* Ref count */
};

/*
** One object per %_data table.
*/
struct Fts5Index {
  Fts5Config *pConfig;            /* Virtual table configuration */
................................................................................
  sqlite3_blob *pReader;          /* RO incr-blob open on %_data table */
  sqlite3_stmt *pWriter;          /* "INSERT ... %_data VALUES(?,?)" */
  sqlite3_stmt *pDeleter;         /* "DELETE FROM %_data ... id>=? AND id<=?" */
  int nRead;                      /* Total number of blocks read */
};

struct Fts5DoclistIter {
  int bDesc;                      /* True for DESC order, false for ASC */
  u8 *a;
  int n;
  int i;

  /* Output variables. aPoslist==0 at EOF */
  i64 iRowid;
  u8 *aPoslist;
................................................................................
/*
** Each iterator used by external modules is an instance of this type.
*/
struct Fts5IndexIter {
  Fts5Index *pIndex;
  Fts5Structure *pStruct;
  Fts5MultiSegIter *pMulti;
  Fts5DoclistIter *pDoclist;
  Fts5Buffer poslist;             /* Buffer containing current poslist */
};

/*
** The contents of the "structure" record for each index are represented
** using an Fts5Structure record in memory. Which uses instances of the 
** other Fts5StructureXXX types as components.
................................................................................
        pBuf->n = nByte;
      }else{
        int nSpace = nByte + FTS5_DATA_ZERO_PADDING;
        pRet = (Fts5Data*)sqlite3Fts5MallocZero(&rc, nSpace+sizeof(Fts5Data));
        if( pRet ){
          pRet->n = nByte;
          aOut = pRet->p = (u8*)&pRet[1];
          pRet->nRef = 1;
        }
      }

      if( rc==SQLITE_OK ){
        rc = sqlite3_blob_read(p->pReader, aOut, nByte, 0);
      }
      if( rc!=SQLITE_OK ){
................................................................................
}

/*
** Release a reference to data record returned by an earlier call to
** fts5DataRead().
*/
static void fts5DataRelease(Fts5Data *pData){
  if( pData ){
    assert( pData->nRef>0 );
    pData->nRef--;
    if( pData->nRef==0 ) sqlite3_free(pData);
  }
}

static void fts5DataReference(Fts5Data *pData){
  pData->nRef++;
}

/*
** INSERT OR REPLACE a record into the %_data table.
*/
static void fts5DataWrite(Fts5Index *p, i64 iRowid, const u8 *pData, int nData){
  if( p->rc!=SQLITE_OK ) return;
................................................................................
  }

  if( pList ){
    Fts5Data *pLeaf;
    sqlite3Fts5BufferSet(&p->rc, &pIter->term, n, z);
    pLeaf = fts5IdxMalloc(p, sizeof(Fts5Data));
    if( pLeaf==0 ) return;
    pLeaf->nRef = 1;
    pLeaf->p = (u8*)pList;
    pLeaf->n = nList;
    pIter->pLeaf = pLeaf;
    pIter->iLeafOffset = getVarint(pLeaf->p, (u64*)&pIter->iRowid);

    if( flags & FTS5INDEX_QUERY_DESC ){
      pIter->flags |= FTS5_SEGITER_REVERSE;
................................................................................
      }
      fts5AssertMultiIterSetup(p, pIter);

      bUseFrom = 0;
    }while( pIter->bSkipEmpty && fts5MultiIterIsEmpty(p, pIter) );
  }
}






















/*
** Allocate a new Fts5MultiSegIter object.
**
** The new object will be used to iterate through data in structure pStruct.
** If iLevel is -ve, then all data in all segments is merged. Or, if iLevel
** is zero or greater, data from the first nSegment segments on level iLevel
................................................................................
  int flags,                      /* FTS5INDEX_QUERY_XXX flags */
  const u8 *pTerm, int nTerm,     /* Term to seek to (or NULL/0) */
  int iLevel,                     /* Level to iterate (-1 for all) */
  int nSegment,                   /* Number of segments to merge (iLevel>=0) */
  Fts5MultiSegIter **ppOut        /* New object */
){
  int nSeg;                       /* Number of segment-iters in use */
  int nSlot = 0;                  /* Power of two >= nSeg */
  int iIter = 0;                  /* */
  int iSeg;                       /* Used to iterate through segments */
  Fts5StructureLevel *pLvl;
  Fts5MultiSegIter *pNew;

  assert( (pTerm==0 && nTerm==0) || iLevel<0 );

................................................................................
    if( iLevel<0 ){
      assert( pStruct->nSegment==fts5StructureCountSegments(pStruct) );
      nSeg = pStruct->nSegment;
      nSeg += (p->pHash ? 1 : 0);
    }else{
      nSeg = MIN(pStruct->aLevel[iLevel].nSeg, nSegment);
    }
    for(nSlot=2; nSlot<nSeg; nSlot=nSlot*2);
  }

  *ppOut = pNew = fts5IdxMalloc(p, 
      sizeof(Fts5MultiSegIter) +          /* pNew */
      sizeof(Fts5SegIter) * nSlot +       /* pNew->aSeg[] */
      sizeof(Fts5CResult) * nSlot         /* pNew->aFirst[] */
  );
  if( pNew==0 ) return;
  pNew->nSeg = nSlot;
  pNew->aSeg = (Fts5SegIter*)&pNew[1];
  pNew->aFirst = (Fts5CResult*)&pNew->aSeg[nSlot];
  pNew->bRev = (0!=(flags & FTS5INDEX_QUERY_DESC));
  pNew->bSkipEmpty = bSkipEmpty;

  /* Initialize each of the component segment iterators. */
  if( iLevel<0 ){
    Fts5StructureLevel *pEnd = &pStruct->aLevel[pStruct->nLevel];
    if( p->pHash ){
................................................................................
  assert( iIter==nSeg );

  /* If the above was successful, each component iterators now points 
  ** to the first entry in its segment. In this case initialize the 
  ** aFirst[] array. Or, if an error has occurred, free the iterator
  ** object and set the output variable to NULL.  */
  if( p->rc==SQLITE_OK ){
    for(iIter=nSlot-1; iIter>0; iIter--){
      int iEq;
      if( (iEq = fts5MultiIterDoCompare(pNew, iIter)) ){
        fts5SegIterNext(p, &pNew->aSeg[iEq], 0);
        fts5MultiIterAdvanced(p, pNew, iEq, iIter);
      }
    }
    fts5AssertMultiIterSetup(p, pNew);
................................................................................
      fts5MultiIterNext(p, pNew, 0, 0);
    }
  }else{
    fts5MultiIterFree(p, pNew);
    *ppOut = 0;
  }
}





































/*
** Return true if the iterator is at EOF or if an error has occurred. 
** False otherwise.
*/
static int fts5MultiIterEof(Fts5Index *p, Fts5MultiSegIter *pIter){
  return (p->rc || pIter->aSeg[ pIter->aFirst[1].iFirst ].pLeaf==0);
................................................................................

static void fts5DoclistIterNext(Fts5DoclistIter *pIter){
  if( pIter->i<pIter->n ){
    int bDummy;
    if( pIter->i ){
      i64 iDelta;
      pIter->i += getVarint(&pIter->a[pIter->i], (u64*)&iDelta);
      if( pIter->bDesc ){
        pIter->iRowid -= iDelta;
      }else{
        pIter->iRowid += iDelta;
      }
    }else{
      pIter->i += getVarint(&pIter->a[pIter->i], (u64*)&pIter->iRowid);
    }
    pIter->i += fts5GetPoslistSize(
        &pIter->a[pIter->i], &pIter->nPoslist, &bDummy
    );
    pIter->aPoslist = &pIter->a[pIter->i];
................................................................................
  }else{
    pIter->aPoslist = 0;
  }
}

static void fts5DoclistIterInit(
  Fts5Buffer *pBuf, 
  int bDesc, 
  Fts5DoclistIter *pIter
){
  memset(pIter, 0, sizeof(*pIter));
  pIter->a = pBuf->p;
  pIter->n = pBuf->n;
  pIter->bDesc = bDesc;
  fts5DoclistIterNext(pIter);
}

/*
** Append a doclist to buffer pBuf.
*/
static void fts5MergeAppendDocid(
  int *pRc,                       /* IN/OUT: Error code */
  int bDesc,
  Fts5Buffer *pBuf,               /* Buffer to write to */
  i64 *piLastRowid,               /* IN/OUT: Previous rowid written (if any) */
  i64 iRowid                      /* Rowid to append */
){
  if( pBuf->n==0 ){
    fts5BufferAppendVarint(pRc, pBuf, iRowid);
  }else if( bDesc ){
    fts5BufferAppendVarint(pRc, pBuf, *piLastRowid - iRowid);
  }else{
    fts5BufferAppendVarint(pRc, pBuf, iRowid - *piLastRowid);
  }
  *piLastRowid = iRowid;
}

/*
................................................................................
** returning.
**
** If an error occurs, an error code is left in p->rc. If an error has
** already occurred, this function is a no-op.
*/
static void fts5MergePrefixLists(
  Fts5Index *p,                   /* FTS5 backend object */
  int bDesc,
  Fts5Buffer *p1,                 /* First list to merge */
  Fts5Buffer *p2                  /* Second list to merge */
){
  if( p2->n ){
    i64 iLastRowid = 0;
    Fts5DoclistIter i1;
    Fts5DoclistIter i2;
    Fts5Buffer out;
    Fts5Buffer tmp;
    memset(&out, 0, sizeof(out));
    memset(&tmp, 0, sizeof(tmp));

    fts5DoclistIterInit(p1, bDesc, &i1);
    fts5DoclistIterInit(p2, bDesc, &i2);
    while( p->rc==SQLITE_OK && (i1.aPoslist!=0 || i2.aPoslist!=0) ){
      if( i2.aPoslist==0 || (i1.aPoslist && 
           ( (bDesc && i1.iRowid>i2.iRowid) || (!bDesc && i1.iRowid<i2.iRowid) )
      )){
        /* Copy entry from i1 */
        fts5MergeAppendDocid(&p->rc, bDesc, &out, &iLastRowid, i1.iRowid);
        /* WRITEPOSLISTSIZE */
        fts5BufferAppendVarint(&p->rc, &out, i1.nPoslist * 2);
        fts5BufferAppendBlob(&p->rc, &out, i1.nPoslist, i1.aPoslist);
        fts5DoclistIterNext(&i1);
      }
      else if( i1.aPoslist==0 || i2.iRowid!=i1.iRowid ){
        /* Copy entry from i2 */
        fts5MergeAppendDocid(&p->rc, bDesc, &out, &iLastRowid, i2.iRowid);
        /* WRITEPOSLISTSIZE */
        fts5BufferAppendVarint(&p->rc, &out, i2.nPoslist * 2);
        fts5BufferAppendBlob(&p->rc, &out, i2.nPoslist, i2.aPoslist);
        fts5DoclistIterNext(&i2);
      }
      else{
        Fts5PoslistReader r1;
        Fts5PoslistReader r2;
        Fts5PoslistWriter writer;

        memset(&writer, 0, sizeof(writer));

        /* Merge the two position lists. */ 
        fts5MergeAppendDocid(&p->rc, bDesc, &out, &iLastRowid, i2.iRowid);
        fts5BufferZero(&tmp);
        sqlite3Fts5PoslistReaderInit(-1, i1.aPoslist, i1.nPoslist, &r1);
        sqlite3Fts5PoslistReaderInit(-1, i2.aPoslist, i2.nPoslist, &r2);
        while( p->rc==SQLITE_OK && (r1.bEof==0 || r2.bEof==0) ){
          i64 iNew;
          if( r2.bEof || (r1.bEof==0 && r1.iPos<r2.iPos) ){
            iNew = r1.iPos;
................................................................................
  const int nBuf = 32;

  aBuf = (Fts5Buffer*)fts5IdxMalloc(p, sizeof(Fts5Buffer)*nBuf);
  pStruct = fts5StructureRead(p);

  if( aBuf && pStruct ){
    const int flags = FTS5INDEX_QUERY_SCAN;
    Fts5DoclistIter *pDoclist;
    int i;
    i64 iLastRowid = 0;
    Fts5MultiSegIter *p1 = 0;     /* Iterator used to gather data from index */

    Fts5Buffer doclist;

    memset(&doclist, 0, sizeof(doclist));
    for(fts5MultiIterNew(p, pStruct, 1, flags, pToken, nToken, -1, 0, &p1);
        fts5MultiIterEof(p, p1)==0;
        fts5MultiIterNext(p, p1, 0, 0)
    ){
      i64 iRowid = fts5MultiIterRowid(p1);
      int nTerm;
      const u8 *pTerm = fts5MultiIterTerm(p1, &nTerm);
      assert( memcmp(pToken, pTerm, MIN(nToken, nTerm))<=0 );
      if( nTerm<nToken || memcmp(pToken, pTerm, nToken) ) break;

      if( doclist.n>0 
       && ((!bDesc && iRowid<=iLastRowid) || (bDesc && iRowid>=iLastRowid))
      ){

        for(i=0; p->rc==SQLITE_OK && doclist.n; i++){
          assert( i<nBuf );
          if( aBuf[i].n==0 ){
            fts5BufferSwap(&doclist, &aBuf[i]);
            fts5BufferZero(&doclist);
          }else{
            fts5MergePrefixLists(p, bDesc, &doclist, &aBuf[i]);
            fts5BufferZero(&aBuf[i]);
          }
        }
      }
      if( doclist.n==0 ){
        fts5BufferAppendVarint(&p->rc, &doclist, iRowid);
      }else if( bDesc ){
        fts5BufferAppendVarint(&p->rc, &doclist, iLastRowid - iRowid);
      }else{
        fts5BufferAppendVarint(&p->rc, &doclist, iRowid - iLastRowid);
      }
      iLastRowid = iRowid;

      fts5MultiIterPoslist(p, p1, 1, &doclist);
    }

    for(i=0; i<nBuf; i++){
      fts5MergePrefixLists(p, bDesc, &doclist, &aBuf[i]);
      fts5BufferFree(&aBuf[i]);
    }
    fts5MultiIterFree(p, p1);

    pDoclist = (Fts5DoclistIter*)fts5IdxMalloc(p, sizeof(Fts5DoclistIter));
    if( !pDoclist ){
      fts5BufferFree(&doclist);
    }else{
      pIter->pDoclist = pDoclist;
      fts5DoclistIterInit(&doclist, bDesc, pIter->pDoclist);
    }

  }

  fts5StructureRelease(pStruct);
  sqlite3_free(aBuf);
}


................................................................................
}

/*
** Return true if the iterator passed as the only argument is at EOF.
*/
int sqlite3Fts5IterEof(Fts5IndexIter *pIter){
  assert( pIter->pIndex->rc==SQLITE_OK );
  if( pIter->pDoclist ){ 
    return pIter->pDoclist->aPoslist==0; 
  }else{
    return fts5MultiIterEof(pIter->pIndex, pIter->pMulti);
  }
}

/*
** Move to the next matching rowid. 
*/
int sqlite3Fts5IterNext(Fts5IndexIter *pIter){
  assert( pIter->pIndex->rc==SQLITE_OK );
  if( pIter->pDoclist ){
    fts5DoclistIterNext(pIter->pDoclist);
  }else{
    fts5BufferZero(&pIter->poslist);
    fts5MultiIterNext(pIter->pIndex, pIter->pMulti, 0, 0);
  }
  return fts5IndexReturn(pIter->pIndex);
}

/*
** Move to the next matching term/rowid. Used by the fts5vocab module.
*/
int sqlite3Fts5IterNextScan(Fts5IndexIter *pIter){
................................................................................
      pSeg->pLeaf = 0;
    }
  }

  return fts5IndexReturn(pIter->pIndex);
}

/*
** Move the doclist-iter passed as the first argument to the next 
** matching rowid that occurs at or after iMatch. The definition of "at 
** or after" depends on whether this iterator iterates in ascending or 
** descending rowid order.
*/
static void fts5DoclistIterNextFrom(Fts5DoclistIter *p, i64 iMatch){
  do{
    i64 iRowid = p->iRowid;
    if( p->bDesc==0 && iRowid>=iMatch ) break;
    if( p->bDesc!=0 && iRowid<=iMatch ) break;
    fts5DoclistIterNext(p);
  }while( p->aPoslist );
}

/*
** Move to the next matching rowid that occurs at or after iMatch. The
** definition of "at or after" depends on whether this iterator iterates
** in ascending or descending rowid order.
*/
int sqlite3Fts5IterNextFrom(Fts5IndexIter *pIter, i64 iMatch){
  if( pIter->pDoclist ){
    fts5DoclistIterNextFrom(pIter->pDoclist, iMatch);
  }else{
    fts5MultiIterNextFrom(pIter->pIndex, pIter->pMulti, iMatch);
  }
  return fts5IndexReturn(pIter->pIndex);
}

/*
** Return the current rowid.
*/
i64 sqlite3Fts5IterRowid(Fts5IndexIter *pIter){
  if( pIter->pDoclist ){
    return pIter->pDoclist->iRowid;
  }else{
    return fts5MultiIterRowid(pIter->pMulti);
  }
}

/*
** Return the current term.
*/
const char *sqlite3Fts5IterTerm(Fts5IndexIter *pIter, int *pn){
  int n;
................................................................................
*/
int sqlite3Fts5IterPoslist(
  Fts5IndexIter *pIter, 
  const u8 **pp,                  /* OUT: Pointer to position-list data */
  int *pn,                        /* OUT: Size of position-list in bytes */
  i64 *piRowid                    /* OUT: Current rowid */
){
  Fts5DoclistIter *pDoclist = pIter->pDoclist;
  assert( pIter->pIndex->rc==SQLITE_OK );
  if( pDoclist ){
    *pn = pDoclist->nPoslist;
    *pp = pDoclist->aPoslist;
    *piRowid = pDoclist->iRowid;
  }else{
    Fts5MultiSegIter *pMulti = pIter->pMulti;
    Fts5SegIter *pSeg = &pMulti->aSeg[ pMulti->aFirst[1].iFirst ];

    *piRowid = pSeg->iRowid;
    *pn = pSeg->nPos;
    if( pSeg->iLeafOffset+pSeg->nPos <= pSeg->pLeaf->n ){
      *pp = &pSeg->pLeaf->p[pSeg->iLeafOffset];
    }else{
      fts5BufferZero(&pIter->poslist);
      fts5SegiterPoslist(pIter->pIndex, pSeg, &pIter->poslist);
      *pp = pIter->poslist.p;
    }
  }
  return fts5IndexReturn(pIter->pIndex);
}

/*
** This function is similar to sqlite3Fts5IterPoslist(), except that it
** copies the position list into the buffer supplied as the second 
** argument.
*/
int sqlite3Fts5IterPoslistBuffer(Fts5IndexIter *pIter, Fts5Buffer *pBuf){
  Fts5Index *p = pIter->pIndex;
  Fts5DoclistIter *pDoclist = pIter->pDoclist;

  assert( p->rc==SQLITE_OK );
  if( pDoclist ){
    fts5BufferSet(&p->rc, pBuf, pDoclist->nPoslist, pDoclist->aPoslist);
  }else{
    Fts5MultiSegIter *pMulti = pIter->pMulti;
    fts5BufferZero(pBuf);
    fts5MultiIterPoslist(p, pMulti, 0, pBuf);
  }
  return fts5IndexReturn(p);
}

/*
** Close an iterator opened by an earlier call to sqlite3Fts5IndexQuery().
*/
void sqlite3Fts5IterClose(Fts5IndexIter *pIter){
  if( pIter ){
    if( pIter->pDoclist ){
      sqlite3_free(pIter->pDoclist->a);
      sqlite3_free(pIter->pDoclist);
    }else{
      fts5MultiIterFree(pIter->pIndex, pIter->pMulti);
      fts5StructureRelease(pIter->pStruct);
      fts5BufferFree(&pIter->poslist);
    }
    fts5CloseReader(pIter->pIndex);
    sqlite3_free(pIter);
  }
}

/*
** Read the "averages" record into the buffer supplied as the second 
................................................................................
  fts5DebugRowid(&rc, &s, iRowid);
  if( bDlidx ){
    Fts5Data dlidx;
    Fts5DlidxLvl lvl;

    dlidx.p = a;
    dlidx.n = n;
    dlidx.nRef = 2;

    memset(&lvl, 0, sizeof(Fts5DlidxLvl));
    lvl.pData = &dlidx;
    lvl.iLeafPgno = iPgno;

    for(fts5DlidxLvlNext(&lvl); lvl.bEof==0; fts5DlidxLvlNext(&lvl)){
      sqlite3Fts5BufferAppendPrintf(&rc, &s, 

typedef struct Fts5Structure Fts5Structure;
typedef struct Fts5StructureLevel Fts5StructureLevel;
typedef struct Fts5StructureSegment Fts5StructureSegment;

struct Fts5Data {
  u8 *p;                          /* Pointer to buffer containing record */
  int n;                          /* Size of record in bytes */

};

/*
** One object per %_data table.
*/
struct Fts5Index {
  Fts5Config *pConfig;            /* Virtual table configuration */
................................................................................
  sqlite3_blob *pReader;          /* RO incr-blob open on %_data table */
  sqlite3_stmt *pWriter;          /* "INSERT ... %_data VALUES(?,?)" */
  sqlite3_stmt *pDeleter;         /* "DELETE FROM %_data ... id>=? AND id<=?" */
  int nRead;                      /* Total number of blocks read */
};

struct Fts5DoclistIter {

  u8 *a;
  int n;
  int i;

  /* Output variables. aPoslist==0 at EOF */
  i64 iRowid;
  u8 *aPoslist;
................................................................................
/*
** Each iterator used by external modules is an instance of this type.
*/
struct Fts5IndexIter {
  Fts5Index *pIndex;
  Fts5Structure *pStruct;
  Fts5MultiSegIter *pMulti;

  Fts5Buffer poslist;             /* Buffer containing current poslist */
};

/*
** The contents of the "structure" record for each index are represented
** using an Fts5Structure record in memory. Which uses instances of the 
** other Fts5StructureXXX types as components.
................................................................................
        pBuf->n = nByte;
      }else{
        int nSpace = nByte + FTS5_DATA_ZERO_PADDING;
        pRet = (Fts5Data*)sqlite3Fts5MallocZero(&rc, nSpace+sizeof(Fts5Data));
        if( pRet ){
          pRet->n = nByte;
          aOut = pRet->p = (u8*)&pRet[1];

        }
      }

      if( rc==SQLITE_OK ){
        rc = sqlite3_blob_read(p->pReader, aOut, nByte, 0);
      }
      if( rc!=SQLITE_OK ){
................................................................................
}

/*
** Release a reference to data record returned by an earlier call to
** fts5DataRead().
*/
static void fts5DataRelease(Fts5Data *pData){



  sqlite3_free(pData);





}

/*
** INSERT OR REPLACE a record into the %_data table.
*/
static void fts5DataWrite(Fts5Index *p, i64 iRowid, const u8 *pData, int nData){
  if( p->rc!=SQLITE_OK ) return;
................................................................................
  }

  if( pList ){
    Fts5Data *pLeaf;
    sqlite3Fts5BufferSet(&p->rc, &pIter->term, n, z);
    pLeaf = fts5IdxMalloc(p, sizeof(Fts5Data));
    if( pLeaf==0 ) return;

    pLeaf->p = (u8*)pList;
    pLeaf->n = nList;
    pIter->pLeaf = pLeaf;
    pIter->iLeafOffset = getVarint(pLeaf->p, (u64*)&pIter->iRowid);

    if( flags & FTS5INDEX_QUERY_DESC ){
      pIter->flags |= FTS5_SEGITER_REVERSE;
................................................................................
      }
      fts5AssertMultiIterSetup(p, pIter);

      bUseFrom = 0;
    }while( pIter->bSkipEmpty && fts5MultiIterIsEmpty(p, pIter) );
  }
}

static Fts5MultiSegIter *fts5MultiIterAlloc(
  Fts5Index *p,                   /* FTS5 backend to iterate within */
  int nSeg
){
  Fts5MultiSegIter *pNew;
  int nSlot;                      /* Power of two >= nSeg */

  for(nSlot=2; nSlot<nSeg; nSlot=nSlot*2);
  pNew = fts5IdxMalloc(p, 
      sizeof(Fts5MultiSegIter) +          /* pNew */
      sizeof(Fts5SegIter) * nSlot +       /* pNew->aSeg[] */
      sizeof(Fts5CResult) * nSlot         /* pNew->aFirst[] */
  );
  if( pNew ){
    pNew->nSeg = nSlot;
    pNew->aSeg = (Fts5SegIter*)&pNew[1];
    pNew->aFirst = (Fts5CResult*)&pNew->aSeg[nSlot];
  }
  return pNew;
}

/*
** Allocate a new Fts5MultiSegIter object.
**
** The new object will be used to iterate through data in structure pStruct.
** If iLevel is -ve, then all data in all segments is merged. Or, if iLevel
** is zero or greater, data from the first nSegment segments on level iLevel
................................................................................
  int flags,                      /* FTS5INDEX_QUERY_XXX flags */
  const u8 *pTerm, int nTerm,     /* Term to seek to (or NULL/0) */
  int iLevel,                     /* Level to iterate (-1 for all) */
  int nSegment,                   /* Number of segments to merge (iLevel>=0) */
  Fts5MultiSegIter **ppOut        /* New object */
){
  int nSeg;                       /* Number of segment-iters in use */

  int iIter = 0;                  /* */
  int iSeg;                       /* Used to iterate through segments */
  Fts5StructureLevel *pLvl;
  Fts5MultiSegIter *pNew;

  assert( (pTerm==0 && nTerm==0) || iLevel<0 );

................................................................................
    if( iLevel<0 ){
      assert( pStruct->nSegment==fts5StructureCountSegments(pStruct) );
      nSeg = pStruct->nSegment;
      nSeg += (p->pHash ? 1 : 0);
    }else{
      nSeg = MIN(pStruct->aLevel[iLevel].nSeg, nSegment);
    }

  }

  *ppOut = pNew = fts5MultiIterAlloc(p, nSeg);




  if( pNew==0 ) return;



  pNew->bRev = (0!=(flags & FTS5INDEX_QUERY_DESC));
  pNew->bSkipEmpty = bSkipEmpty;

  /* Initialize each of the component segment iterators. */
  if( iLevel<0 ){
    Fts5StructureLevel *pEnd = &pStruct->aLevel[pStruct->nLevel];
    if( p->pHash ){
................................................................................
  assert( iIter==nSeg );

  /* If the above was successful, each component iterators now points 
  ** to the first entry in its segment. In this case initialize the 
  ** aFirst[] array. Or, if an error has occurred, free the iterator
  ** object and set the output variable to NULL.  */
  if( p->rc==SQLITE_OK ){
    for(iIter=pNew->nSeg-1; iIter>0; iIter--){
      int iEq;
      if( (iEq = fts5MultiIterDoCompare(pNew, iIter)) ){
        fts5SegIterNext(p, &pNew->aSeg[iEq], 0);
        fts5MultiIterAdvanced(p, pNew, iEq, iIter);
      }
    }
    fts5AssertMultiIterSetup(p, pNew);
................................................................................
      fts5MultiIterNext(p, pNew, 0, 0);
    }
  }else{
    fts5MultiIterFree(p, pNew);
    *ppOut = 0;
  }
}

/*
** Create an Fts5MultiSegIter that iterates through the doclist provided
** as the second argument.
*/
static void fts5MultiIterNew2(
  Fts5Index *p,                   /* FTS5 backend to iterate within */
  Fts5Data *pData,                /* Doclist to iterate through */
  int bDesc,                      /* True for descending rowid order */
  Fts5MultiSegIter **ppOut        /* New object */
){
  Fts5MultiSegIter *pNew;
  pNew = fts5MultiIterAlloc(p, 2);
  if( pNew ){
    Fts5SegIter *pIter = &pNew->aSeg[1];

    pIter->flags = FTS5_SEGITER_ONETERM;
    if( pData->n>0 ){
      pIter->pLeaf = pData;
      pIter->iLeafOffset = getVarint(pData->p, (u64*)&pIter->iRowid);
      pNew->aFirst[1].iFirst = 1;
      if( bDesc ){
        pNew->bRev = 1;
        pIter->flags |= FTS5_SEGITER_REVERSE;
        fts5SegIterReverseInitPage(p, pIter);
      }else{
        fts5SegIterLoadNPos(p, pIter);
      }
      pData = 0;
    }

    *ppOut = pNew;
  }

  fts5DataRelease(pData);
}

/*
** Return true if the iterator is at EOF or if an error has occurred. 
** False otherwise.
*/
static int fts5MultiIterEof(Fts5Index *p, Fts5MultiSegIter *pIter){
  return (p->rc || pIter->aSeg[ pIter->aFirst[1].iFirst ].pLeaf==0);
................................................................................

static void fts5DoclistIterNext(Fts5DoclistIter *pIter){
  if( pIter->i<pIter->n ){
    int bDummy;
    if( pIter->i ){
      i64 iDelta;
      pIter->i += getVarint(&pIter->a[pIter->i], (u64*)&iDelta);



      pIter->iRowid += iDelta;

    }else{
      pIter->i += getVarint(&pIter->a[pIter->i], (u64*)&pIter->iRowid);
    }
    pIter->i += fts5GetPoslistSize(
        &pIter->a[pIter->i], &pIter->nPoslist, &bDummy
    );
    pIter->aPoslist = &pIter->a[pIter->i];
................................................................................
  }else{
    pIter->aPoslist = 0;
  }
}

static void fts5DoclistIterInit(
  Fts5Buffer *pBuf, 

  Fts5DoclistIter *pIter
){
  memset(pIter, 0, sizeof(*pIter));
  pIter->a = pBuf->p;
  pIter->n = pBuf->n;

  fts5DoclistIterNext(pIter);
}

/*
** Append a doclist to buffer pBuf.
*/
static void fts5MergeAppendDocid(
  int *pRc,                       /* IN/OUT: Error code */

  Fts5Buffer *pBuf,               /* Buffer to write to */
  i64 *piLastRowid,               /* IN/OUT: Previous rowid written (if any) */
  i64 iRowid                      /* Rowid to append */
){
  if( pBuf->n==0 ){
    fts5BufferAppendVarint(pRc, pBuf, iRowid);


  }else{
    fts5BufferAppendVarint(pRc, pBuf, iRowid - *piLastRowid);
  }
  *piLastRowid = iRowid;
}

/*
................................................................................
** returning.
**
** If an error occurs, an error code is left in p->rc. If an error has
** already occurred, this function is a no-op.
*/
static void fts5MergePrefixLists(
  Fts5Index *p,                   /* FTS5 backend object */

  Fts5Buffer *p1,                 /* First list to merge */
  Fts5Buffer *p2                  /* Second list to merge */
){
  if( p2->n ){
    i64 iLastRowid = 0;
    Fts5DoclistIter i1;
    Fts5DoclistIter i2;
    Fts5Buffer out;
    Fts5Buffer tmp;
    memset(&out, 0, sizeof(out));
    memset(&tmp, 0, sizeof(tmp));

    fts5DoclistIterInit(p1, &i1);
    fts5DoclistIterInit(p2, &i2);
    while( p->rc==SQLITE_OK && (i1.aPoslist!=0 || i2.aPoslist!=0) ){
      if( i2.aPoslist==0 || (i1.aPoslist && i1.iRowid<i2.iRowid) ){


        /* Copy entry from i1 */
        fts5MergeAppendDocid(&p->rc, &out, &iLastRowid, i1.iRowid);
        /* WRITEPOSLISTSIZE */
        fts5BufferAppendVarint(&p->rc, &out, i1.nPoslist * 2);
        fts5BufferAppendBlob(&p->rc, &out, i1.nPoslist, i1.aPoslist);
        fts5DoclistIterNext(&i1);
      }
      else if( i1.aPoslist==0 || i2.iRowid!=i1.iRowid ){
        /* Copy entry from i2 */
        fts5MergeAppendDocid(&p->rc, &out, &iLastRowid, i2.iRowid);
        /* WRITEPOSLISTSIZE */
        fts5BufferAppendVarint(&p->rc, &out, i2.nPoslist * 2);
        fts5BufferAppendBlob(&p->rc, &out, i2.nPoslist, i2.aPoslist);
        fts5DoclistIterNext(&i2);
      }
      else{
        Fts5PoslistReader r1;
        Fts5PoslistReader r2;
        Fts5PoslistWriter writer;

        memset(&writer, 0, sizeof(writer));

        /* Merge the two position lists. */ 
        fts5MergeAppendDocid(&p->rc, &out, &iLastRowid, i2.iRowid);
        fts5BufferZero(&tmp);
        sqlite3Fts5PoslistReaderInit(-1, i1.aPoslist, i1.nPoslist, &r1);
        sqlite3Fts5PoslistReaderInit(-1, i2.aPoslist, i2.nPoslist, &r2);
        while( p->rc==SQLITE_OK && (r1.bEof==0 || r2.bEof==0) ){
          i64 iNew;
          if( r2.bEof || (r1.bEof==0 && r1.iPos<r2.iPos) ){
            iNew = r1.iPos;
................................................................................
  const int nBuf = 32;

  aBuf = (Fts5Buffer*)fts5IdxMalloc(p, sizeof(Fts5Buffer)*nBuf);
  pStruct = fts5StructureRead(p);

  if( aBuf && pStruct ){
    const int flags = FTS5INDEX_QUERY_SCAN;

    int i;
    i64 iLastRowid = 0;
    Fts5MultiSegIter *p1 = 0;     /* Iterator used to gather data from index */
    Fts5Data *pData;
    Fts5Buffer doclist;

    memset(&doclist, 0, sizeof(doclist));
    for(fts5MultiIterNew(p, pStruct, 1, flags, pToken, nToken, -1, 0, &p1);
        fts5MultiIterEof(p, p1)==0;
        fts5MultiIterNext(p, p1, 0, 0)
    ){
      i64 iRowid = fts5MultiIterRowid(p1);
      int nTerm;
      const u8 *pTerm = fts5MultiIterTerm(p1, &nTerm);
      assert( memcmp(pToken, pTerm, MIN(nToken, nTerm))<=0 );
      if( nTerm<nToken || memcmp(pToken, pTerm, nToken) ) break;

      if( doclist.n>0 && iRowid<=iLastRowid ){



        for(i=0; p->rc==SQLITE_OK && doclist.n; i++){
          assert( i<nBuf );
          if( aBuf[i].n==0 ){
            fts5BufferSwap(&doclist, &aBuf[i]);
            fts5BufferZero(&doclist);
          }else{
            fts5MergePrefixLists(p, &doclist, &aBuf[i]);
            fts5BufferZero(&aBuf[i]);
          }
        }
      }








      fts5MergeAppendDocid(&p->rc, &doclist, &iLastRowid, iRowid);
      fts5MultiIterPoslist(p, p1, 1, &doclist);
    }

    for(i=0; i<nBuf; i++){
      fts5MergePrefixLists(p, &doclist, &aBuf[i]);
      fts5BufferFree(&aBuf[i]);
    }
    fts5MultiIterFree(p, p1);

    pData = fts5IdxMalloc(p, sizeof(Fts5Data) + doclist.n);
    if( pData ){
      pData->p = (u8*)&pData[1];
      pData->n = doclist.n;
      memcpy(pData->p, doclist.p, doclist.n);
      fts5MultiIterNew2(p, pData, bDesc, &pIter->pMulti);
    }
    fts5BufferFree(&doclist);
  }

  fts5StructureRelease(pStruct);
  sqlite3_free(aBuf);
}


................................................................................
}

/*
** Return true if the iterator passed as the only argument is at EOF.
*/
int sqlite3Fts5IterEof(Fts5IndexIter *pIter){
  assert( pIter->pIndex->rc==SQLITE_OK );



  return fts5MultiIterEof(pIter->pIndex, pIter->pMulti);

}

/*
** Move to the next matching rowid. 
*/
int sqlite3Fts5IterNext(Fts5IndexIter *pIter){
  assert( pIter->pIndex->rc==SQLITE_OK );



  fts5BufferZero(&pIter->poslist);
  fts5MultiIterNext(pIter->pIndex, pIter->pMulti, 0, 0);

  return fts5IndexReturn(pIter->pIndex);
}

/*
** Move to the next matching term/rowid. Used by the fts5vocab module.
*/
int sqlite3Fts5IterNextScan(Fts5IndexIter *pIter){
................................................................................
      pSeg->pLeaf = 0;
    }
  }

  return fts5IndexReturn(pIter->pIndex);
}
















/*
** Move to the next matching rowid that occurs at or after iMatch. The
** definition of "at or after" depends on whether this iterator iterates
** in ascending or descending rowid order.
*/
int sqlite3Fts5IterNextFrom(Fts5IndexIter *pIter, i64 iMatch){



  fts5MultiIterNextFrom(pIter->pIndex, pIter->pMulti, iMatch);

  return fts5IndexReturn(pIter->pIndex);
}

/*
** Return the current rowid.
*/
i64 sqlite3Fts5IterRowid(Fts5IndexIter *pIter){



  return fts5MultiIterRowid(pIter->pMulti);

}

/*
** Return the current term.
*/
const char *sqlite3Fts5IterTerm(Fts5IndexIter *pIter, int *pn){
  int n;
................................................................................
*/
int sqlite3Fts5IterPoslist(
  Fts5IndexIter *pIter, 
  const u8 **pp,                  /* OUT: Pointer to position-list data */
  int *pn,                        /* OUT: Size of position-list in bytes */
  i64 *piRowid                    /* OUT: Current rowid */
){







  Fts5MultiSegIter *pMulti = pIter->pMulti;
  Fts5SegIter *pSeg = &pMulti->aSeg[ pMulti->aFirst[1].iFirst ];
  assert( pIter->pIndex->rc==SQLITE_OK );
  *piRowid = pSeg->iRowid;
  *pn = pSeg->nPos;
  if( pSeg->iLeafOffset+pSeg->nPos <= pSeg->pLeaf->n ){
    *pp = &pSeg->pLeaf->p[pSeg->iLeafOffset];
  }else{
    fts5BufferZero(&pIter->poslist);
    fts5SegiterPoslist(pIter->pIndex, pSeg, &pIter->poslist);
    *pp = pIter->poslist.p;

  }
  return fts5IndexReturn(pIter->pIndex);
}

/*
** This function is similar to sqlite3Fts5IterPoslist(), except that it
** copies the position list into the buffer supplied as the second 
** argument.
*/
int sqlite3Fts5IterPoslistBuffer(Fts5IndexIter *pIter, Fts5Buffer *pBuf){
  Fts5Index *p = pIter->pIndex;
  Fts5MultiSegIter *pMulti = pIter->pMulti;

  assert( p->rc==SQLITE_OK );




  fts5BufferZero(pBuf);
  fts5MultiIterPoslist(p, pMulti, 0, pBuf);

  return fts5IndexReturn(p);
}

/*
** Close an iterator opened by an earlier call to sqlite3Fts5IndexQuery().
*/
void sqlite3Fts5IterClose(Fts5IndexIter *pIter){
  if( pIter ){




    fts5MultiIterFree(pIter->pIndex, pIter->pMulti);
    fts5StructureRelease(pIter->pStruct);
    fts5BufferFree(&pIter->poslist);

    fts5CloseReader(pIter->pIndex);
    sqlite3_free(pIter);
  }
}

/*
** Read the "averages" record into the buffer supplied as the second 
................................................................................
  fts5DebugRowid(&rc, &s, iRowid);
  if( bDlidx ){
    Fts5Data dlidx;
    Fts5DlidxLvl lvl;

    dlidx.p = a;
    dlidx.n = n;


    memset(&lvl, 0, sizeof(Fts5DlidxLvl));
    lvl.pData = &dlidx;
    lvl.iLeafPgno = iPgno;

    for(fts5DlidxLvlNext(&lvl); lvl.bEof==0; fts5DlidxLvlNext(&lvl)){
      sqlite3Fts5BufferAppendPrintf(&rc, &s, 

  } {
    foreach {tn prefix} {
      1  {a*} 2 {ab*} 3 {abc*} 4 {abcd*} 5 {abcde*} 
      6  {f*} 7 {fg*} 8 {fgh*} 9 {fghi*} 10 {fghij*}
      11 {k*} 12 {kl*} 13 {klm*} 14 {klmn*} 15 {klmno*}
      16 {p*} 17 {pq*} 18 {pqr*} 19 {pqrs*} 20 {pqrst*}
      21 {u*} 22 {uv*} 23 {uvw*} 24 {uvwx*} 25 {uvwxy*} 26 {uvwxyz*}
      27 {x*} 
      28 {a f*} 29 {a* f*} 30 {a* fghij*}
    } {
      set res [prefix_query $prefix]
      if {$bAsc} {
        set res [lsort -integer -increasing $res]
      }
      set n [llength $res]

  } {
    foreach {tn prefix} {
      1  {a*} 2 {ab*} 3 {abc*} 4 {abcd*} 5 {abcde*} 
      6  {f*} 7 {fg*} 8 {fgh*} 9 {fghi*} 10 {fghij*}
      11 {k*} 12 {kl*} 13 {klm*} 14 {klmn*} 15 {klmno*}
      16 {p*} 17 {pq*} 18 {pqr*} 19 {pqrs*} 20 {pqrst*}
      21 {u*} 22 {uv*} 23 {uvw*} 24 {uvwx*} 25 {uvwxy*} 26 {uvwxyz*}
      27 {x*}
      28 {a f*} 29 {a* f*} 30 {a* fghij*}
    } {
      set res [prefix_query $prefix]
      if {$bAsc} {
        set res [lsort -integer -increasing $res]
      }
      set n [llength $res]