int Field_blob::cmp(const uchar *a_ptr, const uchar *b_ptr)
{
  uchar *blob1,*blob2;
  memcpy(&blob1, a_ptr+packlength, sizeof(char*));
  memcpy(&blob2, b_ptr+packlength, sizeof(char*));
  size_t a_len= get_length(a_ptr), b_len= get_length(b_ptr);
  return cmp(blob1, (uint32)a_len, blob2, (uint32)b_len);
}
int Field_blob::cmp(const uchar *a_ptr, const uchar *b_ptr)
{
  uchar *blob1,*blob2;
  memcpy(&blob1, a_ptr+packlength, sizeof(char*));
  memcpy(&blob2, b_ptr+packlength, sizeof(char*));
  size_t a_len= get_length(a_ptr), b_len= get_length(b_ptr);
  return cmp(blob1, (uint32)a_len, blob2, (uint32)b_len);
}