respect-validation/library/Rules/Cpf.php

<?php
namespace Respect\Validation\Rules;

class Cpf extends AbstractRule
{
    public function validate($input)
    {
        // Code ported from jsfromhell.com
        $c = preg_replace('/\D/', '', $input);

        if (strlen($c) != 11 || preg_match("/^{$c[0]}{11}$/", $c)) {
            return false;
        }

        for ($s = 10, $n = 0, $i = 0; $s >= 2; $n += $c[$i++] * $s--);

        if ($c[9] != ((($n %= 11) < 2) ? 0 : 11 - $n)) {
            return false;
        }

        for ($s = 11, $n = 0, $i = 0; $s >= 2; $n += $c[$i++] * $s--);

        if ($c[10] != ((($n %= 11) < 2) ? 0 : 11 - $n)) {
            return false;
        }

        return true;
    }
}