static int fts3SegWriterAdd(
  Fts3Table *p,                   /* Virtual table handle */
  SegmentWriter **ppWriter,       /* IN/OUT: SegmentWriter handle */ 
  int isCopyTerm,                 /* True if buffer zTerm must be copied */
  const char *zTerm,              /* Pointer to buffer containing term */
  int nTerm,                      /* Size of term in bytes */
  const char *aDoclist,           /* Pointer to buffer containing doclist */
  int nDoclist                    /* Size of doclist in bytes */
){
  int nPrefix;                    /* Size of term prefix in bytes */
  int nSuffix;                    /* Size of term suffix in bytes */
  int nReq;                       /* Number of bytes required on leaf page */
  int nData;
  SegmentWriter *pWriter = *ppWriter;

  if( !pWriter ){
    int rc;
    sqlite3_stmt *pStmt;

    /* Allocate the SegmentWriter structure */
    pWriter = (SegmentWriter *)sqlite3_malloc(sizeof(SegmentWriter));
    if( !pWriter ) return SQLITE_NOMEM;
    memset(pWriter, 0, sizeof(SegmentWriter));
    *ppWriter = pWriter;

    /* Allocate a buffer in which to accumulate data */
    pWriter->aData = (char *)sqlite3_malloc(p->nNodeSize);
    if( !pWriter->aData ) return SQLITE_NOMEM;
    pWriter->nSize = p->nNodeSize;

    /* Find the next free blockid in the %_segments table */
    rc = fts3SqlStmt(p, SQL_NEXT_SEGMENTS_ID, &pStmt, 0);
    if( rc!=SQLITE_OK ) return rc;
    if( SQLITE_ROW==sqlite3_step(pStmt) ){
      pWriter->iFree = sqlite3_column_int64(pStmt, 0);
      pWriter->iFirst = pWriter->iFree;
    }
    rc = sqlite3_reset(pStmt);
    if( rc!=SQLITE_OK ) return rc;
  }
  nData = pWriter->nData;

  nPrefix = fts3PrefixCompress(pWriter->zTerm, pWriter->nTerm, zTerm, nTerm);
  nSuffix = nTerm-nPrefix;

  /* If nSuffix is zero or less, then zTerm/nTerm must be a prefix of 
  ** pWriter->zTerm/pWriter->nTerm. i.e. must be equal to or less than when
  ** compared with BINARY collation. This indicates corruption.  */
  if( nSuffix<=0 ) return FTS_CORRUPT_VTAB;

  /* Figure out how many bytes are required by this new entry */
  nReq = sqlite3Fts3VarintLen(nPrefix) +    /* varint containing prefix size */
    sqlite3Fts3VarintLen(nSuffix) +         /* varint containing suffix size */
    nSuffix +                               /* Term suffix */
    sqlite3Fts3VarintLen(nDoclist) +        /* Size of doclist */
    nDoclist;                               /* Doclist data */

  if( nData>0 && nData+nReq>p->nNodeSize ){
    int rc;

    /* The current leaf node is full. Write it out to the database. */
    rc = fts3WriteSegment(p, pWriter->iFree++, pWriter->aData, nData);
    if( rc!=SQLITE_OK ) return rc;
    p->nLeafAdd++;

    /* Add the current term to the interior node tree. The term added to
    ** the interior tree must:
    **
    **   a) be greater than the largest term on the leaf node just written
    **      to the database (still available in pWriter->zTerm), and
    **
    **   b) be less than or equal to the term about to be added to the new
    **      leaf node (zTerm/nTerm).
    **
    ** In other words, it must be the prefix of zTerm 1 byte longer than
    ** the common prefix (if any) of zTerm and pWriter->zTerm.
    */
    assert( nPrefix<nTerm );
    rc = fts3NodeAddTerm(p, &pWriter->pTree, isCopyTerm, zTerm, nPrefix+1);
    if( rc!=SQLITE_OK ) return rc;

    nData = 0;
    pWriter->nTerm = 0;

    nPrefix = 0;
    nSuffix = nTerm;
    nReq = 1 +                              /* varint containing prefix size */
      sqlite3Fts3VarintLen(nTerm) +         /* varint containing suffix size */
      nTerm +                               /* Term suffix */
      sqlite3Fts3VarintLen(nDoclist) +      /* Size of doclist */
      nDoclist;                             /* Doclist data */
  }

  /* Increase the total number of bytes written to account for the new entry. */
  pWriter->nLeafData += nReq;

  /* If the buffer currently allocated is too small for this entry, realloc
  ** the buffer to make it large enough.
  */
  if( nReq>pWriter->nSize ){
    char *aNew = sqlite3_realloc(pWriter->aData, nReq);
    if( !aNew ) return SQLITE_NOMEM;
    pWriter->aData = aNew;
    pWriter->nSize = nReq;
  }
  assert( nData+nReq<=pWriter->nSize );

  /* Append the prefix-compressed term and doclist to the buffer. */
  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nPrefix);
  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nSuffix);
  assert( nSuffix>0 );
  memcpy(&pWriter->aData[nData], &zTerm[nPrefix], nSuffix);
  nData += nSuffix;
  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nDoclist);
  assert( nDoclist>0 );
  memcpy(&pWriter->aData[nData], aDoclist, nDoclist);
  pWriter->nData = nData + nDoclist;

  /* Save the current term so that it can be used to prefix-compress the next.
  ** If the isCopyTerm parameter is true, then the buffer pointed to by
  ** zTerm is transient, so take a copy of the term data. Otherwise, just
  ** store a copy of the pointer.
  */
  if( isCopyTerm ){
    if( nTerm>pWriter->nMalloc ){
      char *zNew = sqlite3_realloc(pWriter->zMalloc, nTerm*2);
      if( !zNew ){
        return SQLITE_NOMEM;
      }
      pWriter->nMalloc = nTerm*2;
      pWriter->zMalloc = zNew;
      pWriter->zTerm = zNew;
    }
    assert( pWriter->zTerm==pWriter->zMalloc );
    assert( nTerm>0 );
    memcpy(pWriter->zTerm, zTerm, nTerm);
  }else{
    pWriter->zTerm = (char *)zTerm;
  }
  pWriter->nTerm = nTerm;

  return SQLITE_OK;
}
static int fts3SegWriterAdd(
  Fts3Table *p,                    
  SegmentWriter **ppWriter,         
  int isCopyTerm,                  
  const char *zTerm,               
  int nTerm,                       
  const char *aDoclist,            
  int nDoclist                     
){
  int nPrefix;                     
  int nSuffix;                     
  int nReq;                        
  int nData;
  SegmentWriter *pWriter = *ppWriter;

  if( !pWriter ){
    int rc;
    sqlite3_stmt *pStmt;

     
    pWriter = (SegmentWriter *)sqlite3_malloc(sizeof(SegmentWriter));
    if( !pWriter ) return SQLITE_NOMEM;
    memset(pWriter, 0, sizeof(SegmentWriter));
    *ppWriter = pWriter;

     
    pWriter->aData = (char *)sqlite3_malloc(p->nNodeSize);
    if( !pWriter->aData ) return SQLITE_NOMEM;
    pWriter->nSize = p->nNodeSize;

     
    rc = fts3SqlStmt(p, SQL_NEXT_SEGMENTS_ID, &pStmt, 0);
    if( rc!=SQLITE_OK ) return rc;
    if( SQLITE_ROW==sqlite3_step(pStmt) ){
      pWriter->iFree = sqlite3_column_int64(pStmt, 0);
      pWriter->iFirst = pWriter->iFree;
    }
    rc = sqlite3_reset(pStmt);
    if( rc!=SQLITE_OK ) return rc;
  }
  nData = pWriter->nData;

  nPrefix = fts3PrefixCompress(pWriter->zTerm, pWriter->nTerm, zTerm, nTerm);
  nSuffix = nTerm-nPrefix;

   
  if( nSuffix<=0 ) return FTS_CORRUPT_VTAB;

   
  nReq = sqlite3Fts3VarintLen(nPrefix) +     
    sqlite3Fts3VarintLen(nSuffix) +          
    nSuffix +                                
    sqlite3Fts3VarintLen(nDoclist) +         
    nDoclist;                                

  if( nData>0 && nData+nReq>p->nNodeSize ){
    int rc;

     
    rc = fts3WriteSegment(p, pWriter->iFree++, pWriter->aData, nData);
    if( rc!=SQLITE_OK ) return rc;
    p->nLeafAdd++;

     
    assert( nPrefix<nTerm );
    rc = fts3NodeAddTerm(p, &pWriter->pTree, isCopyTerm, zTerm, nPrefix+1);
    if( rc!=SQLITE_OK ) return rc;

    nData = 0;
    pWriter->nTerm = 0;

    nPrefix = 0;
    nSuffix = nTerm;
    nReq = 1 +                               
      sqlite3Fts3VarintLen(nTerm) +          
      nTerm +                                
      sqlite3Fts3VarintLen(nDoclist) +       
      nDoclist;                              
  }

   
  pWriter->nLeafData += nReq;

   
  if( nReq>pWriter->nSize ){
    char *aNew = sqlite3_realloc(pWriter->aData, nReq);
    if( !aNew ) return SQLITE_NOMEM;
    pWriter->aData = aNew;
    pWriter->nSize = nReq;
  }
  assert( nData+nReq<=pWriter->nSize );

   
  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nPrefix);
  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nSuffix);
  assert( nSuffix>0 );
  memcpy(&pWriter->aData[nData], &zTerm[nPrefix], nSuffix);
  nData += nSuffix;
  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nDoclist);
  assert( nDoclist>0 );
  memcpy(&pWriter->aData[nData], aDoclist, nDoclist);
  pWriter->nData = nData + nDoclist;

   
  if( isCopyTerm ){
    if( nTerm>pWriter->nMalloc ){
      char *zNew = sqlite3_realloc(pWriter->zMalloc, nTerm*2);
      if( !zNew ){
        return SQLITE_NOMEM;
      }
      pWriter->nMalloc = nTerm*2;
      pWriter->zMalloc = zNew;
      pWriter->zTerm = zNew;
    }
    assert( pWriter->zTerm==pWriter->zMalloc );
    assert( nTerm>0 );
    memcpy(pWriter->zTerm, zTerm, nTerm);
  }else{
    pWriter->zTerm = (char *)zTerm;
  }
  pWriter->nTerm = nTerm;

  return SQLITE_OK;
}