SQLite

/*
** Value for the first field of every RtreeMatchArg object. The MATCH
** operator tests that the first field of a blob operand matches this
** value to avoid operating on invalid blobs (which could cause a segfault).
*/
#define RTREE_GEOMETRY_MAGIC 0x891245AB
#define RTREE_GEOMETRY_SUBTYPE 0x52

/*
** An instance of this structure (in the form of a BLOB) is returned by
** the SQL functions that sqlite3_rtree_geometry_callback() and
** sqlite3_rtree_query_callback() create, and is read as the right-hand
** operand to the MATCH operator of an R-Tree.
*/

static int deserializeGeometry(sqlite3_value *pValue, RtreeConstraint *pCons){
  RtreeMatchArg *pBlob;              /* BLOB returned by geometry function */
  sqlite3_rtree_query_info *pInfo;   /* Callback information */
  int nBlob;                         /* Size of the geometry function blob */
  int nExpected;                     /* Expected size of the BLOB */

  /* Check that value is actually a blob. */
  if( sqlite3_value_type(pValue)!=SQLITE_BLOB ) return SQLITE_ERROR;
  if( sqlite3_value_type(pValue)!=SQLITE_BLOB
   || sqlite3_value_subtype(pValue)!=RTREE_GEOMETRY_SUBTYPE
  ){
    return SQLITE_ERROR;
  }

  /* Check that the blob is roughly the right size. */
  nBlob = sqlite3_value_bytes(pValue);
  if( nBlob<(int)sizeof(RtreeMatchArg) ){
    return SQLITE_ERROR;
  }

#endif
    }
    if( memErr ){
      sqlite3_result_error_nomem(ctx);
      rtreeMatchArgFree(pBlob);
    }else{
      sqlite3_result_blob(ctx, pBlob, nBlob, rtreeMatchArgFree);
      sqlite3_result_subtype(ctx, RTREE_GEOMETRY_SUBTYPE);
    }
  }
}

/*
** Register a new geometry function for use with the r-tree MATCH operator.
*/