shuffle string

function shuffle_string($string) {
    $len = strlen($string);
    for ($i = 0; $i < $len; $i++) {
        $pos = rand(0, $len - 1);
        $temp = $string[$i];
        $string[$i] = $string[$pos];
        $string[$pos] = $temp;
    }
    return $string;
}