Pi calculation

function gcd($a,$b) {
    while($a > 0 && $b > 0) {
        if($a > $b)
            $a %= $b;
        else
            $b %= $a;
    }
    return $a + $b;
}

function pi_calc($n) {
  $m = 0;
  for($i = 1; $i <= $n; $i++) {
     $a = mt_rand();
     $b = mt_rand();
     if (gcd($a,$b) == 1) $m++;
  }
  return sqrt((6 * $n) / $m);
}

echo pi_calc(1000)