PHP : GCD

gcd.php

<?php

/**
 * Calculate Greatest Common Divisor of 2 integers.
 * The result is always positive even if either of, or both, input operands are negative.
 *
 * @param int $a
 * @param int $b
 * @return int
 */
function gcd($a, $b)
{
    $a = abs((int) $a);
    $b = abs((int) $b);

    if ((0 == $a) || (0 == $b)) {
        $gcd = 1;
    } elseif ($a == $b) {
        $gcd = $a;
    } else {
        if ($a < $b) {
            $rest = $a;
            $a = $b;
            $b = $rest;
        }

        do {
            $rest = $a % $b;
            $a = $b;
            $b = $rest;
        } while (0 !== $rest);

        $gcd = $a;
    }

    return $gcd;
}