};

/*
** An instance of the following type is used to iterate through the contents
** of a doclist-index record.
**
** pData:
**   A reference to the dlidx record.






*/
struct Fts5DlidxIter {
  Fts5Data *pData;              /* Data for doclist index, if any */
  int iOff;                     /* Current offset into pDlidx */
  int bRowidValid;              /* iRowid is valid */
  int bEof;                     /* At EOF already */


  /* Output variables */
  int iLeafPgno;                /* Page number of current leaf page */
  int bZero;                    /* True if current leaf has no rowids */
  i64 iRowid;                   /* If bZero==0, first rowid on leaf */
};


/*
** An Fts5BtreeIter object is used to iterate through all entries in the
** b-tree hierarchy belonging to a single fts5 segment. In this case the
** "b-tree hierarchy" is all b-tree nodes except leaves. Each entry in the
................................................................................
** Free any memory allocated by the iterator object.
*/
static void fts5NodeIterFree(Fts5NodeIter *pIter){
  fts5BufferFree(&pIter->term);
}

/*
** Return non-zero if EOF is reached.





*/




























static int fts5DlidxIterNext(Fts5DlidxIter *pIter, int bRev){
  if( bRev ){








    i64 iVal;























    int iOff = pIter->iOff;
    int iLimit;





    u8 *a = pIter->pData->p;



    /* Currently iOff points to the first byte of a varint. This block 
    ** decrements iOff until it points to the first byte of the previous 
    ** varint. Taking care not to read any memory locations that occur
    ** before the buffer in memory.  */
    iLimit = (iOff>9 ? iOff-9 : 0);
    for(iOff--; iOff>iLimit; iOff--){
      if( (a[iOff-1] & 0x80)==0 ) break;
    }
    pIter->iOff = iOff;

    if( iOff<=0 ){
      pIter->bEof = 1;
      return 1;
    }

    getVarint(&a[iOff], (u64*)&iVal);
    if( iVal==0 ){
      pIter->bZero = 1;
    }else if( iOff==0 ){
      pIter->iRowid = iVal;
    }else{
      pIter->iRowid += iVal;
    }
    pIter->iLeafPgno--;
  }else{
    i64 iVal;
    if( pIter->iOff>=pIter->pData->n ){
      pIter->bEof = 1;
      return 1;
    }
    pIter->iOff += getVarint(&pIter->pData->p[pIter->iOff], (u64*)&iVal);
    if( iVal==0 ){
      pIter->bZero = 1;
    }else{
      pIter->bZero = 0;
      if( pIter->bRowidValid ){
        pIter->iRowid -= iVal;
      }else{
        pIter->bRowidValid = 1;
        pIter->iRowid = iVal;
      }
    }


    pIter->iLeafPgno++;
  }
  return 0;
}

static void fts5DlidxIterLast(Fts5DlidxIter *pIter){
  while( 0==fts5DlidxIterNext(pIter, 0) );
  assert( pIter->iOff==pIter->pData->n && pIter->bEof==1 );
  pIter->bEof = 0;
}

static int fts5DlidxIterEof(Fts5Index *p, Fts5DlidxIter *pIter){
  return (p->rc!=SQLITE_OK || pIter->bEof);
}

static void fts5DlidxIterInit(
  Fts5Index *p,                   /* Fts5 Backend to iterate within */
  int bRev,                       /* True for ORDER BY ASC */
  int iIdx, int iSegid,           /* Segment iSegid within index iIdx */
  int iLeafPgno,                  /* Leaf page number to load dlidx for */
................................................................................
      return;
    }
  }else{
    memset(pIter, 0, sizeof(Fts5DlidxIter));
  }

  pIter->pData = pDlidx;

  pIter->iLeafPgno = iLeafPgno;
  if( bRev==0 ){
    fts5DlidxIterNext(pIter, 0);
  }else{
    fts5DlidxIterLast(pIter);
  }
}

/*
** Free a doclist-index iterator object allocated by fts5DlidxIterInit().
................................................................................
        pIter->iLeafOffset = iOff = pIter->aRowidOffset[pIter->iRowidOffset];
        iOff += getVarint32(&a[iOff], nPos);
        iOff += nPos;
        getVarint(&a[iOff], (u64*)&iDelta);
        pIter->iRowid += iDelta;
      }else{
        fts5SegIterReverseNewPage(p, pIter);
#if 0
        fts5DataRelease(pIter->pLeaf);
        pIter->pLeaf = 0;
        while( p->rc==SQLITE_OK && pIter->iLeafPgno>pIter->iTermLeafPgno ){
          Fts5Data *pNew;
          pIter->iLeafPgno--;
          pNew = fts5DataRead(p, FTS5_SEGMENT_ROWID(
                pIter->iIdx, pIter->pSeg->iSegid, 0, pIter->iLeafPgno
          ));
          if( pNew ){
            if( pIter->iLeafPgno==pIter->iTermLeafPgno ){
              if( pIter->iTermLeafOffset<pNew->n ){
                pIter->pLeaf = pNew;
                pIter->iLeafOffset = pIter->iTermLeafOffset;
              }
            }else{
              int iRowidOff, dummy;
              fts5LeafHeader(pNew, &iRowidOff, &dummy);
              if( iRowidOff ){
                pIter->pLeaf = pNew;
                pIter->iLeafOffset = iRowidOff;
              }
            }

            if( pIter->pLeaf ){
              u8 *a = &pIter->pLeaf->p[pIter->iLeafOffset];
              pIter->iLeafOffset += getVarint(a, (u64*)&pIter->iRowid);
              break;
            }else{
              fts5DataRelease(pNew);
            }
          }
        }

        if( pIter->pLeaf ){
          fts5SegIterReverseInitPage(p, pIter);
        }
#endif
      }
    }else{
      Fts5Data *pLeaf = pIter->pLeaf;
      int iOff;
      int bNewTerm = 0;
      int nKeep = 0;

................................................................................
  int iOff = pIter->iLeafOffset;  /* Byte offset within current leaf */
  Fts5Data *pLast = 0;
  int pgnoLast = 0;

  /* Move to the page that contains the last rowid in this doclist. */
  pLeaf = pIter->pLeaf;






  while( iOff<pLeaf->n ){
    int nPos;
    i64 iDelta;

    /* Position list size in bytes */
    iOff += getVarint32(&pLeaf->p[iOff], nPos);
    iOff += nPos;
    if( iOff>=pLeaf->n ) break;

    /* Rowid delta. Or, if 0x00, the end of doclist marker. */
    nPos = getVarint(&pLeaf->p[iOff], (u64*)&iDelta);
    if( iDelta==0 ) break;
    iOff += nPos;
  }

  if( iOff>=pLeaf->n ){
    Fts5StructureSegment *pSeg = pIter->pSeg;
    i64 iAbs = FTS5_SEGMENT_ROWID(iIdx, pSeg->iSegid, 0, pIter->iLeafPgno);
    i64 iLast = FTS5_SEGMENT_ROWID(iIdx, pSeg->iSegid, 0, pSeg->pgnoLast);

    /* The last rowid in the doclist may not be on the current page. Search
    ** forward to find the page containing the last rowid.  */
    for(iAbs++; p->rc==SQLITE_OK && iAbs<=iLast; iAbs++){
      Fts5Data *pNew = fts5DataRead(p, iAbs);
      if( pNew ){
        int iRowid, iTerm;
        fts5LeafHeader(pNew, &iRowid, &iTerm);
        if( iRowid ){
          Fts5Data *pTmp = pLast;
          pLast = pNew;
          pNew = pTmp;
          pgnoLast = iAbs & (((i64)1 << FTS5_DATA_PAGE_B) - 1);
        }
        if( iTerm ){
          iAbs = iLast;
        }
        fts5DataRelease(pNew);

      }
    }
  }

  /* If pLast is NULL at this point, then the last rowid for this doclist
  ** lies on the page currently indicated by the iterator. In this case 
  ** iLastOff is set to the value that pIter->iLeafOffset will take when
................................................................................
    pIter->iLeafPgno = pgnoLast;
    fts5LeafHeader(pLast, &iOff, &dummy);
    iOff += getVarint(&pLast->p[iOff], (u64*)&pIter->iRowid);
    pIter->iLeafOffset = iOff;
  }

  fts5SegIterReverseInitPage(p, pIter);
  pIter->flags |= FTS5_SEGITER_REVERSE;
}

/*
** Iterator pIter currently points to the first rowid of a doclist within
** index iIdx. There is a doclist-index associated with the final term on
** the current page. If the current term is the last term on the page, 
** load the doclist-index from disk and initialize an iterator at 
................................................................................
      pIter->pLeaf = 0;
    }
  }

  if( bGe==0 ){
    pIter->flags |= FTS5_SEGITER_ONETERM;
    if( pIter->pLeaf ){



      if( bDlidx ){
        fts5SegIterLoadDlidx(p, iIdx, pIter);
      }
      if( flags & FTS5INDEX_QUERY_ASC ){
        fts5SegIterReverse(p, iIdx, pIter);
      }
    }
................................................................................
  Fts5Index *p,                   /* FTS5 backend object */
  Fts5SegIter *pIter,             /* Iterator to advance */
  i64 iMatch                      /* Advance iterator at least this far */
){
  int bRev = (pIter->flags & FTS5_SEGITER_REVERSE);
  Fts5DlidxIter *pDlidx = pIter->pDlidx;
  int iLeafPgno = pIter->iLeafPgno;


  assert( pIter->flags & FTS5_SEGITER_ONETERM );
  assert( pIter->pDlidx );
  assert( pIter->pLeaf );


  if( bRev==0 ){
    while( fts5DlidxIterEof(p, pDlidx)==0 && iMatch<pDlidx->iRowid ){
      if( pDlidx->bZero==0 ) iLeafPgno = pDlidx->iLeafPgno;
      fts5DlidxIterNext(pDlidx, 0);
    }
    assert( iLeafPgno>=pIter->iLeafPgno || p->rc );
    if( iLeafPgno>pIter->iLeafPgno ){
      fts5SegIterGotoPage(p, pIter, iLeafPgno);

    }
  }else if( 0 ){

    while( fts5DlidxIterEof(p, pDlidx)==0 && iMatch>pDlidx->iRowid ){
      fts5DlidxIterNext(pDlidx, 0);

      if( pDlidx->bZero==0 ) iLeafPgno = pDlidx->iLeafPgno;
    }
    assert( iLeafPgno<=pIter->iLeafPgno || p->rc );

    if( iLeafPgno<pIter->iLeafPgno ){
      fts5SegIterGotoPage(p, pIter, iLeafPgno);



    }
  }

  while( 1 ){
    fts5SegIterNext(p, pIter);
    if( pIter->pLeaf==0 ) break;
    if( bRev==0 && pIter->iRowid<=iMatch ) break;
    if( bRev!=0 && pIter->iRowid>=iMatch ) break;

  }
}

/*
** Move the iterator to the next entry. 
**
** If an error occurs, an error code is left in Fts5Index.rc. It is not 
................................................................................
      pLvl->pData = 0;
    }
  }
  sqlite3_free(pIter->aLvl);
  fts5BufferFree(&pIter->term);
}














































static void fts5IndexIntegrityCheckSegment(
  Fts5Index *p,                   /* FTS5 backend object */
  int iIdx,                       /* Index that pSeg is a part of */
  Fts5StructureSegment *pSeg      /* Segment to check internal consistency */
){
  Fts5BtreeIter iter;             /* Used to iterate through b-tree hierarchy */
................................................................................
      if( res<0 ){
        p->rc = FTS5_CORRUPT;
      }
    }
    fts5DataRelease(pLeaf);
    if( p->rc ) break;


    /* Now check that the iter.nEmpty leaves following the current leaf
    ** (a) exist and (b) contain no terms. */
    for(i=1; p->rc==SQLITE_OK && i<=iter.nEmpty; i++){
      pLeaf = fts5DataRead(p, iRow+i);
      if( pLeaf && 0!=fts5GetU16(&pLeaf->p[2]) ){
        p->rc = FTS5_CORRUPT;
      }
      fts5DataRelease(pLeaf);
    }

    /* If there is a doclist-index, check that it looks right. */
    if( iter.bDlidx ){
      Fts5DlidxIter *pDlidx = 0;  /* For iterating through doclist index */
      int nEntry = 0;
      int iSegid = pSeg->iSegid;
      int bRev = 0;


      for(fts5DlidxIterInit(p, bRev, iIdx, iSegid, iter.iLeaf, &pDlidx);
          fts5DlidxIterEof(p, pDlidx)==0;
          fts5DlidxIterNext(pDlidx, bRev)
      ){



        i64 iKey = FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, pDlidx->iLeafPgno);
        pLeaf = fts5DataRead(p, iKey);
        if( pLeaf ){
          int iRowidOff = fts5GetU16(&pLeaf->p[0]);
          if( pDlidx->bZero ){
            if( iRowidOff!=0 ) p->rc = FTS5_CORRUPT;
          }else{










            i64 iRowid;

            getVarint(&pLeaf->p[iRowidOff], (u64*)&iRowid);
            if( iRowid!=pDlidx->iRowid ) p->rc = FTS5_CORRUPT;
          }
          fts5DataRelease(pLeaf);
        }
        nEntry++;
      }

      /* Check that the doclist-index was the right length */
      if( p->rc==SQLITE_OK && nEntry!=iter.nEmpty && nEntry!=iter.nEmpty+1 ){





        p->rc = FTS5_CORRUPT;

      }


      fts5DlidxIterFree(pDlidx);

    }
  }

  if( p->rc==SQLITE_OK && iter.iLeaf!=pSeg->pgnoLast ){
    p->rc = FTS5_CORRUPT;
  }

};

/*
** An instance of the following type is used to iterate through the contents
** of a doclist-index record.
**
** pData:
**   Record containing the doclist-index data.
**
** bEof:
**   Set to true once iterator has reached EOF.
**
** iOff:
**   Set to the current offset within record pData.
*/
struct Fts5DlidxIter {
  Fts5Data *pData;              /* Data for doclist index, if any */
  int iOff;                     /* Current offset into pDlidx */

  int bEof;                     /* At EOF already */
  int iFirstOff;                /* Used by reverse iterators only */

  /* Output variables */
  int iLeafPgno;                /* Page number of current leaf page */

  i64 iRowid;                   /* First rowid on leaf iLeafPgno */
};


/*
** An Fts5BtreeIter object is used to iterate through all entries in the
** b-tree hierarchy belonging to a single fts5 segment. In this case the
** "b-tree hierarchy" is all b-tree nodes except leaves. Each entry in the
................................................................................
** Free any memory allocated by the iterator object.
*/
static void fts5NodeIterFree(Fts5NodeIter *pIter){
  fts5BufferFree(&pIter->term);
}

/*
** The iterator passed as the first argument has the following fields set
** as follows. This function sets up the rest of the iterator so that it
** points to the first rowid in the doclist-index.
**
**   pData: pointer to doclist-index record, 
**   iLeafPgno: page number that this doclist-index is associated with.
*/
static int fts5DlidxIterFirst(Fts5DlidxIter *pIter){
  Fts5Data *pData = pIter->pData;
  int i;

  assert( pIter->pData );
  assert( pIter->iLeafPgno>0 );

  /* Count the number of leading 0x00 bytes. Then set iLeafPgno. */
  for(i=0; i<pData->n; i++){ 
    if( pData->p[i] ) break;
  }
  pIter->iLeafPgno += (i+1);
  pIter->iOff = i;

  /* Unless we are already at the end of the doclist-index, load the first
  ** rowid value.  */
  if( pIter->iOff<pData->n ){
    pIter->iOff += getVarint(&pData->p[pIter->iOff], (u64*)&pIter->iRowid);
  }else{
    pIter->bEof = 1;
  }
  pIter->iFirstOff = pIter->iOff;
  return pIter->bEof;
}

/*
** Advance the iterator passed as the only argument.
*/
static int fts5DlidxIterNext(Fts5DlidxIter *pIter){

  Fts5Data *pData = pIter->pData;
  int iOff;

  for(iOff=pIter->iOff; iOff<pData->n; iOff++){
    if( pData->p[iOff] ) break; 
  }

  if( iOff<pData->n ){
    i64 iVal;
    pIter->iLeafPgno += (iOff - pIter->iOff) + 1;
    iOff += getVarint(&pData->p[iOff], (u64*)&iVal);
    pIter->iRowid -= iVal;
    pIter->iOff = iOff;
  }else{
    pIter->bEof = 1;
  }

  return pIter->bEof;
}

static int fts5DlidxIterEof(Fts5Index *p, Fts5DlidxIter *pIter){
  return (p->rc!=SQLITE_OK || pIter->bEof);
}

static void fts5DlidxIterLast(Fts5DlidxIter *pIter){
  if( fts5DlidxIterFirst(pIter)==0 ){
    while( 0==fts5DlidxIterNext(pIter) );
    pIter->bEof = 0;
  }
}

static int fts5DlidxIterPrev(Fts5DlidxIter *pIter){
  int iOff = pIter->iOff;


  assert( pIter->bEof==0 );
  if( iOff<=pIter->iFirstOff ){
    pIter->bEof = 1;
  }else{
    u8 *a = pIter->pData->p;
    i64 iVal;
    int iLimit;

    /* Currently iOff points to the first byte of a varint. This block 
    ** decrements iOff until it points to the first byte of the previous 
    ** varint. Taking care not to read any memory locations that occur
    ** before the buffer in memory.  */
    iLimit = (iOff>9 ? iOff-9 : 0);
    for(iOff--; iOff>iLimit; iOff--){
      if( (a[iOff-1] & 0x80)==0 ) break;
    }







    getVarint(&a[iOff], (u64*)&iVal);





    pIter->iRowid += iVal;

    pIter->iLeafPgno--;


















    while( a[iOff-1]==0x00 ){
      iOff--;
      pIter->iLeafPgno--;
    }






    pIter->iOff = iOff;
  }


  return pIter->bEof;
}

static void fts5DlidxIterInit(
  Fts5Index *p,                   /* Fts5 Backend to iterate within */
  int bRev,                       /* True for ORDER BY ASC */
  int iIdx, int iSegid,           /* Segment iSegid within index iIdx */
  int iLeafPgno,                  /* Leaf page number to load dlidx for */
................................................................................
      return;
    }
  }else{
    memset(pIter, 0, sizeof(Fts5DlidxIter));
  }

  pIter->pData = pDlidx;

  pIter->iLeafPgno = iLeafPgno;
  if( bRev==0 ){
    fts5DlidxIterFirst(pIter);
  }else{
    fts5DlidxIterLast(pIter);
  }
}

/*
** Free a doclist-index iterator object allocated by fts5DlidxIterInit().
................................................................................
        pIter->iLeafOffset = iOff = pIter->aRowidOffset[pIter->iRowidOffset];
        iOff += getVarint32(&a[iOff], nPos);
        iOff += nPos;
        getVarint(&a[iOff], (u64*)&iDelta);
        pIter->iRowid += iDelta;
      }else{
        fts5SegIterReverseNewPage(p, pIter);






































      }
    }else{
      Fts5Data *pLeaf = pIter->pLeaf;
      int iOff;
      int bNewTerm = 0;
      int nKeep = 0;

................................................................................
  int iOff = pIter->iLeafOffset;  /* Byte offset within current leaf */
  Fts5Data *pLast = 0;
  int pgnoLast = 0;

  /* Move to the page that contains the last rowid in this doclist. */
  pLeaf = pIter->pLeaf;

  if( pIter->pDlidx ){
    int iSegid = pIter->pSeg->iSegid;
    pgnoLast = pIter->pDlidx->iLeafPgno;
    pLast = fts5DataRead(p, FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, pgnoLast));
  }else{
    while( iOff<pLeaf->n ){
      int nPos;
      i64 iDelta;

      /* Position list size in bytes */
      iOff += getVarint32(&pLeaf->p[iOff], nPos);
      iOff += nPos;
      if( iOff>=pLeaf->n ) break;

      /* Rowid delta. Or, if 0x00, the end of doclist marker. */
      nPos = getVarint(&pLeaf->p[iOff], (u64*)&iDelta);
      if( iDelta==0 ) break;
      iOff += nPos;
    }

    if( iOff>=pLeaf->n ){
      Fts5StructureSegment *pSeg = pIter->pSeg;
      i64 iAbs = FTS5_SEGMENT_ROWID(iIdx, pSeg->iSegid, 0, pIter->iLeafPgno);
      i64 iLast = FTS5_SEGMENT_ROWID(iIdx, pSeg->iSegid, 0, pSeg->pgnoLast);

      /* The last rowid in the doclist may not be on the current page. Search
       ** forward to find the page containing the last rowid.  */
      for(iAbs++; p->rc==SQLITE_OK && iAbs<=iLast; iAbs++){
        Fts5Data *pNew = fts5DataRead(p, iAbs);
        if( pNew ){
          int iRowid, iTerm;
          fts5LeafHeader(pNew, &iRowid, &iTerm);
          if( iRowid ){
            Fts5Data *pTmp = pLast;
            pLast = pNew;
            pNew = pTmp;
            pgnoLast = iAbs & (((i64)1 << FTS5_DATA_PAGE_B) - 1);
          }
          if( iTerm ){
            iAbs = iLast;
          }
          fts5DataRelease(pNew);
        }
      }
    }
  }

  /* If pLast is NULL at this point, then the last rowid for this doclist
  ** lies on the page currently indicated by the iterator. In this case 
  ** iLastOff is set to the value that pIter->iLeafOffset will take when
................................................................................
    pIter->iLeafPgno = pgnoLast;
    fts5LeafHeader(pLast, &iOff, &dummy);
    iOff += getVarint(&pLast->p[iOff], (u64*)&pIter->iRowid);
    pIter->iLeafOffset = iOff;
  }

  fts5SegIterReverseInitPage(p, pIter);

}

/*
** Iterator pIter currently points to the first rowid of a doclist within
** index iIdx. There is a doclist-index associated with the final term on
** the current page. If the current term is the last term on the page, 
** load the doclist-index from disk and initialize an iterator at 
................................................................................
      pIter->pLeaf = 0;
    }
  }

  if( bGe==0 ){
    pIter->flags |= FTS5_SEGITER_ONETERM;
    if( pIter->pLeaf ){
      if( flags & FTS5INDEX_QUERY_ASC ){
        pIter->flags |= FTS5_SEGITER_REVERSE;
      }
      if( bDlidx ){
        fts5SegIterLoadDlidx(p, iIdx, pIter);
      }
      if( flags & FTS5INDEX_QUERY_ASC ){
        fts5SegIterReverse(p, iIdx, pIter);
      }
    }
................................................................................
  Fts5Index *p,                   /* FTS5 backend object */
  Fts5SegIter *pIter,             /* Iterator to advance */
  i64 iMatch                      /* Advance iterator at least this far */
){
  int bRev = (pIter->flags & FTS5_SEGITER_REVERSE);
  Fts5DlidxIter *pDlidx = pIter->pDlidx;
  int iLeafPgno = pIter->iLeafPgno;
  int bMove = 1;

  assert( pIter->flags & FTS5_SEGITER_ONETERM );
  assert( pIter->pDlidx );
  assert( pIter->pLeaf );


  if( bRev==0 ){
    while( fts5DlidxIterEof(p, pDlidx)==0 && iMatch<pDlidx->iRowid ){
      iLeafPgno = pDlidx->iLeafPgno;
      fts5DlidxIterNext(pDlidx);
    }
    assert( iLeafPgno>=pIter->iLeafPgno || p->rc );
    if( iLeafPgno>pIter->iLeafPgno ){
      fts5SegIterGotoPage(p, pIter, iLeafPgno);
      bMove = 0;
    }
  }else{
    assert( iMatch>pIter->iRowid );
    while( fts5DlidxIterEof(p, pDlidx)==0 && iMatch>pDlidx->iRowid ){
      fts5DlidxIterPrev(pDlidx);
    }
    iLeafPgno = pDlidx->iLeafPgno;

    assert( fts5DlidxIterEof(p, pDlidx) || iLeafPgno<=pIter->iLeafPgno );

    if( iLeafPgno<pIter->iLeafPgno ){

      pIter->iLeafPgno = iLeafPgno+1;
      fts5SegIterReverseNewPage(p, pIter);
      bMove = 0;
    }
  }

  while( 1 ){
    if( bMove ) fts5SegIterNext(p, pIter);
    if( pIter->pLeaf==0 ) break;
    if( bRev==0 && pIter->iRowid<=iMatch ) break;
    if( bRev!=0 && pIter->iRowid>=iMatch ) break;
    bMove = 1;
  }
}

/*
** Move the iterator to the next entry. 
**
** If an error occurs, an error code is left in Fts5Index.rc. It is not 
................................................................................
      pLvl->pData = 0;
    }
  }
  sqlite3_free(pIter->aLvl);
  fts5BufferFree(&pIter->term);
}

/*
** This function is purely an internal test. It does not contribute to 
** FTS functionality, or even the integrity-check, in any way.
**
** Instead, it tests that the same set of pgno/rowid combinations are 
** visited regardless of whether the doclist-index identified by parameters
** iIdx/iSegid/iLeaf is iterated in forwards or reverse order.
*/
#ifdef SQLITE_DEBUG
static void fts5DlidxIterTestReverse(
  Fts5Index *p, 
  int iIdx,                       /* Index to load doclist-index from */
  int iSegid,                     /* Segment id to load from */
  int iLeaf                       /* Load doclist-index for this leaf */
){
  Fts5DlidxIter *pDlidx = 0;
  i64 cksum1 = 13;
  i64 cksum2 = 13;

  for(fts5DlidxIterInit(p, 0, iIdx, iSegid, iLeaf, &pDlidx);
      fts5DlidxIterEof(p, pDlidx)==0;
      fts5DlidxIterNext(pDlidx)
  ){
    cksum1 = (cksum1 ^ ( (i64)(pDlidx->iLeafPgno) << 32 ));
    cksum1 = (cksum1 ^ pDlidx->iRowid);
  }
  fts5DlidxIterFree(pDlidx);
  pDlidx = 0;

  for(fts5DlidxIterInit(p, 1, iIdx, iSegid, iLeaf, &pDlidx);
      fts5DlidxIterEof(p, pDlidx)==0;
      fts5DlidxIterPrev(pDlidx)
  ){
    cksum2 = (cksum2 ^ ( (i64)(pDlidx->iLeafPgno) << 32 ));
    cksum2 = (cksum2 ^ pDlidx->iRowid);
  }
  fts5DlidxIterFree(pDlidx);
  pDlidx = 0;

  if( p->rc==SQLITE_OK && cksum1!=cksum2 ) p->rc = FTS5_CORRUPT; 
}
#else
# define fts5DlidxIterTestReverse(w,x,y,z)
#endif

static void fts5IndexIntegrityCheckSegment(
  Fts5Index *p,                   /* FTS5 backend object */
  int iIdx,                       /* Index that pSeg is a part of */
  Fts5StructureSegment *pSeg      /* Segment to check internal consistency */
){
  Fts5BtreeIter iter;             /* Used to iterate through b-tree hierarchy */
................................................................................
      if( res<0 ){
        p->rc = FTS5_CORRUPT;
      }
    }
    fts5DataRelease(pLeaf);
    if( p->rc ) break;


    /* Now check that the iter.nEmpty leaves following the current leaf
    ** (a) exist and (b) contain no terms. */
    for(i=1; p->rc==SQLITE_OK && i<=iter.nEmpty; i++){
      pLeaf = fts5DataRead(p, iRow+i);
      if( pLeaf && 0!=fts5GetU16(&pLeaf->p[2]) ){
        p->rc = FTS5_CORRUPT;
      }
      fts5DataRelease(pLeaf);
    }

    /* If there is a doclist-index, check that it looks right. */
    if( iter.bDlidx ){
      Fts5DlidxIter *pDlidx = 0;  /* For iterating through doclist index */
      int iPrevLeaf = iter.iLeaf;
      int iSegid = pSeg->iSegid;
      int iPg;
      i64 iKey;

      for(fts5DlidxIterInit(p, 0, iIdx, iSegid, iter.iLeaf, &pDlidx);
          fts5DlidxIterEof(p, pDlidx)==0;
          fts5DlidxIterNext(pDlidx)
      ){

        /* Check any rowid-less pages that occur before the current leaf. */
        for(iPg=iPrevLeaf+1; iPg<pDlidx->iLeafPgno; iPg++){
          iKey = FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, iPg);
          pLeaf = fts5DataRead(p, iKey);
          if( pLeaf ){


            if( fts5GetU16(&pLeaf->p[0])!=0 ) p->rc = FTS5_CORRUPT;

            fts5DataRelease(pLeaf);
          }
        }
        iPrevLeaf = pDlidx->iLeafPgno;

        /* Check that the leaf page indicated by the iterator really does
        ** contain the rowid suggested by the same. */
        iKey = FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, pDlidx->iLeafPgno);
        pLeaf = fts5DataRead(p, iKey);
        if( pLeaf ){
          i64 iRowid;
          int iRowidOff = fts5GetU16(&pLeaf->p[0]);
          getVarint(&pLeaf->p[iRowidOff], (u64*)&iRowid);
          if( iRowid!=pDlidx->iRowid ) p->rc = FTS5_CORRUPT;

          fts5DataRelease(pLeaf);
        }


      }



      for(iPg=iPrevLeaf+1; iPg<=(iter.iLeaf + iter.nEmpty); iPg++){
        iKey = FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, iPg);
        pLeaf = fts5DataRead(p, iKey);
        if( pLeaf ){
          if( fts5GetU16(&pLeaf->p[0])!=0 ) p->rc = FTS5_CORRUPT;
          fts5DataRelease(pLeaf);
        }
      }

      fts5DlidxIterFree(pDlidx);
      fts5DlidxIterTestReverse(p, iIdx, iSegid, iter.iLeaf);
    }
  }

  if( p->rc==SQLITE_OK && iter.iLeaf!=pSeg->pgnoLast ){
    p->rc = FTS5_CORRUPT;
  }

do_execsql_test 6.2 {
  INSERT INTO t1(t1) VALUES('integrity-check') 
}

#-------------------------------------------------------------------------
#
reset_db

do_execsql_test 7.0 {
  CREATE VIRTUAL TABLE t1 USING fts5(x,y,z);
  INSERT INTO t1(t1) VALUES('pgsz=32');
}

proc doc {} {
  set v [list aaa aab abc abcde b c d dd ddd dddd ddddd]
................................................................................
      puts "[lrange $lvl 0 1] $seg"
    }
  }
}

for {set i 1} {$i <= 10} {incr i} {
  do_test 7.$i {
    for {set j 0} {$j < 100} {incr j} {
      set x [doc]
      set y [doc]
      set z [doc]
      set rowid [expr int(rand() * 100)]
      execsql { REPLACE INTO t1(rowid,x,y,z) VALUES($rowid, $x, $y, $z) }
    }
    execsql { INSERT INTO t1(t1) VALUES('integrity-check'); }

do_execsql_test 6.2 {
  INSERT INTO t1(t1) VALUES('integrity-check') 
}

#-------------------------------------------------------------------------
#
reset_db
expr srand(0)
do_execsql_test 7.0 {
  CREATE VIRTUAL TABLE t1 USING fts5(x,y,z);
  INSERT INTO t1(t1) VALUES('pgsz=32');
}

proc doc {} {
  set v [list aaa aab abc abcde b c d dd ddd dddd ddddd]
................................................................................
      puts "[lrange $lvl 0 1] $seg"
    }
  }
}

for {set i 1} {$i <= 10} {incr i} {
  do_test 7.$i {
    for {set j 0} {$j < 10} {incr j} {
      set x [doc]
      set y [doc]
      set z [doc]
      set rowid [expr int(rand() * 100)]
      execsql { REPLACE INTO t1(rowid,x,y,z) VALUES($rowid, $x, $y, $z) }
    }
    execsql { INSERT INTO t1(t1) VALUES('integrity-check'); }

  1 {a b} {[N $x -- {a}] && [N $x -- {b}]}
} {
  do_execsql_test 5.$tn {SELECT fts5_expr_tcl($expr, 'N $x')} [list $tclexpr]
}

#-------------------------------------------------------------------------
#




foreach {bAsc sql} {
  0 {SELECT rowid FROM xx WHERE xx MATCH $expr}
  1 {SELECT rowid FROM xx WHERE xx MATCH $expr ORDER BY rowid ASC}
} {
  foreach {tn expr} {
    0.1 x
    1 { NEAR(r c) }

  1 {a b} {[N $x -- {a}] && [N $x -- {b}]}
} {
  do_execsql_test 5.$tn {SELECT fts5_expr_tcl($expr, 'N $x')} [list $tclexpr]
}

#-------------------------------------------------------------------------
#
do_execsql_test 6.integrity {
  INSERT INTO xx(xx) VALUES('integrity-check');
}
#db eval {SELECT rowid, fts5_decode(rowid, block) aS r FROM xx_data} {puts $r}
foreach {bAsc sql} {
  0 {SELECT rowid FROM xx WHERE xx MATCH $expr}
  1 {SELECT rowid FROM xx WHERE xx MATCH $expr ORDER BY rowid ASC}
} {
  foreach {tn expr} {
    0.1 x
    1 { NEAR(r c) }

do_execsql_test 1.3 {
  INSERT INTO t1(t1) VALUES('integrity-check');
}

proc reads {} {
  db one {SELECT t1 FROM t1 WHERE t1 MATCH '*reads'}
}







do_test 1.4 {
  set nRead [reads]
  execsql { SELECT rowid FROM t1 WHERE t1 MATCH 'x' }
  set nReadX [expr [reads] - $nRead]
  expr $nReadX>1000
} {1}









foreach {tn q res} "
  1 { SELECT rowid FROM t1 WHERE t1 MATCH 'w + x'   }  [list $W]
  2 { SELECT rowid FROM t1 WHERE t1 MATCH 'x + w'   }  [list $W]
  3 { SELECT rowid FROM t1 WHERE t1 MATCH 'x AND w' }  [list $W]
  4 { SELECT rowid FROM t1 WHERE t1 MATCH 'y AND x' }  [list $Y]
" {

  do_test 1.5.$tn.1 {
    set nRead [reads]
    execsql $q

    set n [expr [reads] - $nRead]



    expr {$n < ($nReadX / 10)}
  } {1}

  do_test 1.5.$tn.2 {
    set nRead [reads]
    execsql "$q ORDER BY rowid ASC"
    set n [expr [reads] - $nRead]
    expr {$n < ($nReadX / 10)}
  } {1}

  do_execsql_test 1.5.$tn.3 $q [lsort -int -decr $res]
  do_execsql_test 1.5.$tn.4 "$q ORDER BY rowid ASC" [lsort -int -incr $res]
}

#db eval {SELECT rowid, fts5_decode(rowid, block) aS r FROM t1_data} {puts $r}

finish_test

do_execsql_test 1.3 {
  INSERT INTO t1(t1) VALUES('integrity-check');
}

proc reads {} {
  db one {SELECT t1 FROM t1 WHERE t1 MATCH '*reads'}
}

proc execsql_reads {sql} {
  set nRead [reads]
  execsql $sql
  expr [reads] - $nRead
}

do_test 1.4 {
  set nRead [reads]
  execsql { SELECT rowid FROM t1 WHERE t1 MATCH 'x' }
  set nReadX [expr [reads] - $nRead]
  expr $nReadX>1000
} {1}

do_test 1.5 {
  set fwd [execsql_reads {SELECT rowid FROM t1 WHERE t1 MATCH 'x' }]
  set bwd [execsql_reads {
    SELECT rowid FROM t1 WHERE t1 MATCH 'x' ORDER BY 1 ASC 
  }]
  expr {$bwd < $fwd + 10}
} {1}

foreach {tn q res} "
  1 { SELECT rowid FROM t1 WHERE t1 MATCH 'w + x'   }  [list $W]
  2 { SELECT rowid FROM t1 WHERE t1 MATCH 'x + w'   }  [list $W]
  3 { SELECT rowid FROM t1 WHERE t1 MATCH 'x AND w' }  [list $W]
  4 { SELECT rowid FROM t1 WHERE t1 MATCH 'y AND x' }  [list $Y]
" {

  do_test 1.6.$tn.1 {

    set n [execsql_reads $q]
    expr {$n < ($nReadX / 10)}
  } {1}

  do_test 1.6.$tn.2 {
    set n [execsql_reads "$q ORDER BY rowid ASC"]
    expr {$n < ($nReadX / 10)}
  } {1}








  do_execsql_test 1.6.$tn.3 $q [lsort -int -decr $res]
  do_execsql_test 1.6.$tn.4 "$q ORDER BY rowid ASC" [lsort -int -incr $res]
}

#db eval {SELECT rowid, fts5_decode(rowid, block) aS r FROM t1_data} {puts $r}

finish_test