private function gcd($a, $b)
    {
        return $b ? $this->gcd($b, $a % $b) : $a;
    }
private function gcd($a, $b)
    {
        return $b ? $this->gcd($b, $a % $b) : $a;
    }
private function gcd ( $ a , $ b ) { return $ b ? $ this -> gcd ( $ b , $ a % $ b ) : $ a ; }
Get the greater common divisor between two numbers.

@param int $a
The first number
@param int $b
The second number

@return int
The greater common divisor between $a and $b
Get the greater common divisor between two numbers .