Arithmetic Operations without using the operations

add.php

<?php
/**
 * Add number without using any arithmetic operators.
 * @author thachp * 
 **/
 
// add & subject
function add($a, $b) {
    if ($b === 0) return $a;
    $sum = $a ^ $b; // add		
    $carry = ($a & $b) << 1; // add without carry		
	//echo("sum:" . $sum . ' - '.  decbin($sum) . ", " . "carry:" . $carry . " - " .  decbin($carry) . "\n \n");
    return add($sum, $carry);
};

echo("<pre>");
//echo("5,3 : " . decbin(5) . " + " .  decbin(3) . "\n");
echo (add(5,3));
echo("\n");
echo (add(5,-3));
echo("</pre>");
?>