SQLite

** the end. Hence these functions allow the caller to handle the
** serial-type and data blob seperately.
**
** The following table describes the various storage classes for data:
**
**   serial type        bytes of data      type
**   --------------     ---------------    ---------------
**      0                     -            Not a type.
**      1                     1            signed integer
**      2                     2            signed integer
**      3                     4            signed integer
**      4                     8            signed integer
**      5                     8            IEEE float
**      6                     0            NULL
**     7..11                               reserved for expansion
**    N>=12 and even       (N-12)/2        BLOB
**    N>=13 and odd        (N-13)/2        text
**
*/

/*
** Return the serial-type for the value stored in pMem.
*/
u64 sqlite3VdbeSerialType(const Mem *pMem){
  int flags = pMem->flags;

  if( flags&MEM_Null ){
    return 6;
  }
  if( flags&MEM_Int ){
    /* Figure out whether to use 1, 2, 4 or 8 bytes. */
    i64 i = pMem->i;
    if( i>=-127 && i<=127 ) return 1;
    if( i>=-32767 && i<=32767 ) return 2;
    if( i>=-2147483647 && i<=2147483647 ) return 3;

  return 0;
}

/*
** Return the length of the data corresponding to the supplied serial-type.
*/
int sqlite3VdbeSerialTypeLen(u64 serial_type){
  assert( serial_type!=0 );
  switch(serial_type){
    case 6: return 0;                  /* NULL */
    case 1: return 1;                  /* 1 byte integer */
    case 2: return 2;                  /* 2 byte integer */
    case 3: return 4;                  /* 4 byte integer */
    case 4: return 8;                  /* 8 byte integer */
    case 5: return 8;                  /* 8 byte float */
  }
  assert( serial_type>=12 );
  return ((serial_type-12)>>1);        /* text or blob */
}

/*
** Write the serialized data blob for the value stored in pMem into 
** buf. It is assumed that the caller has allocated sufficient space.
** Return the number of bytes written.
*/ 
int sqlite3VdbeSerialPut(unsigned char *buf, const Mem *pMem){
  u64 serial_type = sqlite3VdbeSerialType(pMem);
  int len;

  assert( serial_type!=0 );
 
  /* NULL */
  if( serial_type==6 ){
    return 0;
  }
 
  /* Integer */
  if( serial_type<5 ){
    i64 i = pMem->i;
    len = sqlite3VdbeSerialTypeLen(serial_type);

/*
** Deserialize the data blob pointed to by buf as serial type serial_type
** and store the result in pMem.  Return the number of bytes read.
*/ 
int sqlite3VdbeSerialGet(const unsigned char *buf, u64 serial_type, Mem *pMem){
  int len;

  assert( serial_type!=0 );

  /* memset(pMem, 0, sizeof(pMem)); */
  pMem->flags = 0;
  pMem->z = 0;

  /* NULL */
  if( serial_type==6 ){
    pMem->flags = MEM_Null;
    return 0;
  }
 
  /* Integer */
  if( serial_type<5 ){
    i64 i = 0;

/*
** The following is the comparison function for (non-integer)
** keys in the btrees.  This function returns negative, zero, or
** positive if the first key is less than, equal to, or greater than
** the second.
**
** This function assumes that each key consists of one or more type/blob
** pairs, encoded using the sqlite3VdbeSerialXXX() functions above. 
**
** Following the type/blob pairs, each key may have a single 0x00 byte
** followed by a varint. A key may only have this traling 0x00/varint
** pair if it has at least as many type/blob pairs as the key it is being
** compared to.
*/
int sqlite3VdbeKeyCompare(
  void *userData,                         /* not used yet */
  int nKey1, const void *pKey1, 
  int nKey2, const void *pKey2
){
  int offset1 = 0;
  int offset2 = 0;
  const unsigned char *aKey1 = (const unsigned char *)pKey1;
  const unsigned char *aKey2 = (const unsigned char *)pKey2;
  
  while( offset1<nKey1 && offset2<nKey2 ){
    Mem mem1;
    Mem mem2;
    u64 serial_type1;
    u64 serial_type2;
    int rc;

    /* Read the serial types for the next element in each key. */
    offset1 += sqlite3GetVarint(&aKey1[offset1], &serial_type1);
    offset2 += sqlite3GetVarint(&aKey2[offset2], &serial_type2);

    /* If either of the varints just read in are 0 (not a type), then
    ** this is the end of the keys. The remaining data in each key is
    ** the varint rowid. Compare these as signed integers and return
    ** the result.
    */
    if( !serial_type1 || !serial_type2 ){
      assert( !serial_type1 && !serial_type2 );
      sqlite3GetVarint(&aKey1[offset1], &serial_type1);
      sqlite3GetVarint(&aKey2[offset2], &serial_type2);
      return ( (i64)serial_type1 - (i64)serial_type2 );
    }

    /* Assert that there is enough space left in each key for the blob of
    ** data to go with the serial type just read. This assert may fail if
    ** the file is corrupted.  Then read the value from each key into mem1
    ** and mem2 respectively.
    */
    offset1 += sqlite3VdbeSerialGet(&aKey1[offset1], serial_type1, &mem1);
    offset2 += sqlite3VdbeSerialGet(&aKey2[offset2], serial_type2, &mem2);

    rc = compareMemCells(&mem1, &mem2);
    if( mem1.flags&MEM_Dyn ){
      sqliteFree(mem1.z);
    }

    return 1;
  }
  if( offset2<nKey2 ){
    return -1;
  }
  return 0;
}

/*
** pCur points at an index entry. Read the rowid (varint occuring at
** the end of the entry and store it in *rowid. Return SQLITE_OK if
** everything works, or an error code otherwise.
*/
int sqlite3VdbeIdxRowid(BtCursor *pCur, i64 *rowid){
  i64 sz;
  int rc;
  char buf[9];
  int len;
  u64 r;

  rc = sqlite3BtreeKeySize(pCur, &sz);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  len = ((sz>9)?9:sz);
  assert( len>=2 );

  rc = sqlite3BtreeKey(pCur, sz-len, len, buf);
  if( rc!=SQLITE_OK ){
    return rc;
  }

  len = len - 2;
  while( buf[len] && --len );

  sqlite3GetVarint(buf, &r);
  *rowid = r;
  return SQLITE_OK;
}

int sqlite3VdbeIdxKeyCompare(
  BtCursor *pCur, 
  int nKey, const unsigned char *pKey,
  int ignorerowid,
  int *res
){
  unsigned char *pCellKey;
  u64 nCellKey;
  int freeCellKey = 0;
  int rc;
  int len;

  sqlite3BtreeKeySize(pCur, &nCellKey);
  if( nCellKey<=0 ){
    *res = 0;
    return SQLITE_OK;
  }

  pCellKey = (unsigned char *)sqlite3BtreeKeyFetch(pCur, nCellKey);
  if( !pCellKey ){
    pCellKey = (unsigned char *)sqliteMalloc(nCellKey);
    if( !pCellKey ){
      return SQLITE_NOMEM;
    }
    freeCellKey = 1;
    rc = sqlite3BtreeKey(pCur, 0, nCellKey, pCellKey);
    if( rc!=SQLITE_OK ){
      sqliteFree(pCellKey);
      return rc;
    }
  }
 
  len = nCellKey-2;
  while( pCellKey[len] && --len );

  if( ignorerowid ){
    nKey--;
    while( pKey[nKey] && --nKey );
  }
  *res = sqlite3VdbeKeyCompare(0, len, pCellKey, nKey, pKey);
  
  if( freeCellKey ){
    sqliteFree(pCellKey);
  }
  return SQLITE_OK;
}