/**
* Get modulus of an arbitrary precision number
*
* @param string $n The left operand, as a string.
* @param string $d The modulus, as a string.
* @access public
* @return string Returns the modulus as a string, or <b>NULL</b> if modulus is 0.
*/
public function mod($n, $d)
{
$n = new Math_BigInteger($n);
$d = new Math_BigInteger($d);
return $n->_mod2($d);
}
