SQLite

** A phrase. One or more terms that must appear in a contiguous sequence
** within a document for it to match.
*/
struct Fts5ExprPhrase {
  Fts5ExprNode *pNode;            /* FTS5_STRING node this phrase is part of */
  Fts5Buffer poslist;             /* Current position list */
  int nTerm;                      /* Number of entries in aTerm[] */
  Fts5ExprTerm aTerm[1];          /* Terms that make up this phrase */
};

/*
** If a NEAR() clump may only match a specific set of columns, then
** Fts5ExprNearset.pColset points to an object of the following type.
** Each entry in the aiCol[] array
*/
struct Fts5ExprColset {
  int nCol;
  int aiCol[1];
};

/*
** One or more phrases that must appear within a certain token distance of
** each other within each matching document.
*/
struct Fts5ExprNearset {
  int nNear;                      /* NEAR parameter */
  Fts5ExprColset *pColset;        /* Columns to search (NULL -> all columns) */
  int nPhrase;                    /* Number of entries in aPhrase[] array */
  Fts5ExprPhrase *apPhrase[1];    /* Array of phrase pointers */
};


/*
** Parse context.
*/
struct Fts5Parse {

  int iSzPoslist;                 /* Offset of space for 4-byte poslist size */
  int nData;                      /* Total bytes of data (incl. structure) */
  u8 bDel;                        /* Set delete-flag @ iSzPoslist */

  int iCol;                       /* Column of last value written */
  int iPos;                       /* Position of last value written */
  i64 iRowid;                     /* Rowid of last value written */
  char zKey[8];                   /* Nul-terminated entry key */
};

/*
** Size of Fts5HashEntry without the zKey[] array.
*/
#define FTS5_HASHENTRYSIZE (sizeof(Fts5HashEntry)-8)



/*
** Allocate a new hash table.
*/
int sqlite3Fts5HashNew(Fts5Hash **ppNew, int *pnByte){
  int rc = SQLITE_OK;
  Fts5Hash *pNew;

    ){
      break;
    }
  }

  /* If an existing hash entry cannot be found, create a new one. */
  if( p==0 ){
    int nByte = FTS5_HASHENTRYSIZE + (nToken+1) + 1 + 64;
    if( nByte<128 ) nByte = 128;

    if( (pHash->nEntry*2)>=pHash->nSlot ){
      int rc = fts5HashResize(pHash);
      if( rc!=SQLITE_OK ) return rc;
      iHash = fts5HashKey2(pHash->nSlot, bByte, pToken, nToken);
    }

    p = (Fts5HashEntry*)sqlite3_malloc(nByte);
    if( !p ) return SQLITE_NOMEM;
    memset(p, 0, FTS5_HASHENTRYSIZE);
    p->nAlloc = nByte;
    p->zKey[0] = bByte;
    memcpy(&p->zKey[1], pToken, nToken);
    assert( iHash==fts5HashKey(pHash->nSlot, p->zKey, nToken+1) );
    p->zKey[nToken+1] = '\0';
    p->nData = nToken+1 + 1 + FTS5_HASHENTRYSIZE;
    p->nData += sqlite3Fts5PutVarint(&((u8*)p)[p->nData], iRowid);
    p->iSzPoslist = p->nData;
    p->nData += 1;
    p->iRowid = iRowid;
    p->pHashNext = pHash->aSlot[iHash];
    pHash->aSlot[iHash] = p;
    pHash->nEntry++;

  for(p=pHash->aSlot[iHash]; p; p=p->pHashNext){
    if( memcmp(p->zKey, pTerm, nTerm)==0 && p->zKey[nTerm]==0 ) break;
  }

  if( p ){
    fts5HashAddPoslistSize(p);
    *ppDoclist = (const u8*)&p->zKey[nTerm+1];
    *pnDoclist = p->nData - (FTS5_HASHENTRYSIZE + nTerm + 1);
  }else{
    *ppDoclist = 0;
    *pnDoclist = 0;
  }

  return SQLITE_OK;
}

){
  Fts5HashEntry *p;
  if( (p = pHash->pScan) ){
    int nTerm = strlen(p->zKey);
    fts5HashAddPoslistSize(p);
    *pzTerm = p->zKey;
    *ppDoclist = (const u8*)&p->zKey[nTerm+1];
    *pnDoclist = p->nData - (FTS5_HASHENTRYSIZE + nTerm + 1);
  }else{
    *pzTerm = 0;
    *ppDoclist = 0;
    *pnDoclist = 0;
  }
}

  Fts5StructureSegment *aSeg;     /* Array of segments. aSeg[0] is oldest. */
};
struct Fts5Structure {
  int nRef;                       /* Object reference count */
  u64 nWriteCounter;              /* Total leaves written to level 0 */
  int nSegment;                   /* Total segments in this structure */
  int nLevel;                     /* Number of levels in this index */
  Fts5StructureLevel aLevel[1];   /* Array of nLevel level objects */
};

/*
** An object of type Fts5SegWriter is used to write to segments.
*/
struct Fts5PageWriter {
  int pgno;                       /* Page number for this page */

  /* Read the total number of levels and segments from the start of the
  ** structure record.  */
  i += fts5GetVarint32(&pData[i], nLevel);
  i += fts5GetVarint32(&pData[i], nSegment);
  nByte = (
      sizeof(Fts5Structure) +                    /* Main structure */
      sizeof(Fts5StructureLevel) * (nLevel-1)    /* aLevel[] array */
  );
  pRet = (Fts5Structure*)sqlite3Fts5MallocZero(&rc, nByte);

  if( pRet ){
    pRet->nRef = 1;
    pRet->nLevel = nLevel;
    pRet->nSegment = nSegment;

** any currently existing segment. If a free segment id cannot be found,
** SQLITE_FULL is returned.
**
** If an error has already occurred, this function is a no-op. 0 is 
** returned in this case.
*/
static int fts5AllocateSegid(Fts5Index *p, Fts5Structure *pStruct){
  int iSegid = 0;

  if( p->rc==SQLITE_OK ){
    if( pStruct->nSegment>=FTS5_MAX_SEGMENT ){
      p->rc = SQLITE_FULL;
    }else{
      while( iSegid==0 ){
        int iLvl, iSeg;
        sqlite3_randomness(sizeof(u32), (void*)&iSegid);
        iSegid = iSegid & ((1 << FTS5_DATA_ID_B)-1);

        for(iLvl=0; iLvl<pStruct->nLevel; iLvl++){
          for(iSeg=0; iSeg<pStruct->aLevel[iLvl].nSeg; iSeg++){
            if( iSegid==pStruct->aLevel[iLvl].aSeg[iSeg].iSegid ){
              iSegid = 0;
            }
          }
        }
      }
    }
  }

  return iSegid;
}

/*
** Discard all data currently cached in the hash-tables.
*/
static void fts5IndexDiscardData(Fts5Index *p){
  assert( p->pHash || p->nPendingData==0 );

**   byte of the position list for the corresponding phrase.
*/
struct Fts5Sorter {
  sqlite3_stmt *pStmt;
  i64 iRowid;                     /* Current rowid */
  const u8 *aPoslist;             /* Position lists for current row */
  int nIdx;                       /* Number of entries in aIdx[] */
  int aIdx[1];                    /* Offsets into aPoslist for current row */
};


/*
** Virtual-table cursor object.
**
** iSpecial:

  int nByte;
  int rc = SQLITE_OK;
  char *zSql;
  const char *zRank = pCsr->zRank;
  const char *zRankArgs = pCsr->zRankArgs;
  
  nPhrase = sqlite3Fts5ExprPhraseCount(pCsr->pExpr);
  nByte = sizeof(Fts5Sorter) + sizeof(int) * (nPhrase-1);
  pSorter = (Fts5Sorter*)sqlite3_malloc(nByte);
  if( pSorter==0 ) return SQLITE_NOMEM;
  memset(pSorter, 0, nByte);
  pSorter->nIdx = nPhrase;

  /* TODO: It would be better to have some system for reusing statement
  ** handles here, rather than preparing a new one for each query. But that