code: public static function GCD(...$args)
      {
          $args = Functions::flattenArray($args);
          // Loop through arguments
          foreach (Functions::flattenArray($args) as $value) {
              if (!is_numeric($value)) {
                  return Functions::VALUE();
              } elseif ($value < 0) {
                  return Functions::NAN();
              }
          }
  
          $gcd = (int) array_pop($args);
          do {
              $gcd = self::evaluateGCD($gcd, (int) array_pop($args));
          } while (!empty($args));
  
          return $gcd;
      }
docs: GCD.
  
  Returns the greatest common divisor of a series of numbers.
  The greatest common divisor is the largest integer that divides both
  number1 and number2 without a remainder.
  
  Excel Function:
  GCD(number1[,number2[, ...]])
  
  @category Mathematical and Trigonometric Functions
  
  @param mixed ...$args Data values
  
  @return int Greatest Common Divisor