<?php
// this code is from an article located at https://linuxwebdevelopment.com/find-gcd-two-integers-php/
function gcd($x,$y) {
  // if $y > $x, then switch them
  if ($y > $x) {
    $temp1 = $y;
    $y = $x;
    $x = $temp1;
  }

  // edge cases. If x or y are negative, if one or both of them is a 0, or if they are the same number.
  if ($x == 0 && $y == 0) return 1;
  if ($x == 0) return $y;
  if ($y == 0) return $x;
  if ($x < 0) $x = -$x;
  if ($y < 0) $y = -$y;
  if ($x == $y) return $x;

  // Using the Euclidean algorithm with x being the divisor and y being the remainder for each step after the first step
  while ($y > 0) {
    $temp2 = $y;
    $y = $x % $y;
    $x = $temp2;
  }
  
  // return the divisor when the remainder is 0
  return $x;
}

?>