Some values returned by gmp_strval are padded with an additional \0 byte.

The code

  for ($i = 0; $i < 20; $i++) {
      $n = gmp_init($i);
      $ns = gmp_strval($n);
      print ord(substr($ns, -1)) . ' ';
  }

outputs

  48 49 50 51 52 53 54 55 0 0 48 49 50 51 52 53 54 55 56 57 

where I would expect

  48 49 50 51 52 53 54 55 56 57 48 49 50 51 52 53 54 55 56 57


This behavior is reproducible.