fiscal code validator

<?php
/**
 * ConstraintFiscalCodeValidator.php.
 * @author Andrea Giuliano <giulianoand@gmail.com>
 * Date: 20/07/12
 * Time: 16:19
 */
namespace Dnsee\RegistrationBundle\Validator\Constraints;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;
use Dnsee\RegistrationBundle\Entity\User;

class ConstraintFiscalCodeSyntaxValidator extends ConstraintValidator
{

    const REGEX_CF = '/^([A-Z]{6}[0-9LMNPQRSTUV]{2}[ABCDEHLMPRST]{1}[0-9LMNPQRSTUV]{2}[A-Za-z]{1}[0-9LMNPQRSTUV]{3}[A-Za-z]{1})$/i';

    /**
     * @param $user
     * @param Symfony\Component\Validator\Constraint $constraint
     */
    public function isValid($fiscalCode, Constraint $constraint)
    {
        $fiscalCode = strtoupper(str_replace(" ", "", $fiscalCode));

        if ( !$this->checkSyntax($fiscalCode) ||
             !$this->checkDigit($fiscalCode)
           )
        {
            $this->context->addViolationAtSubPath('fiscal_code', $constraint->message);
        }
    }

    protected function checkSyntax($value)
    {
        return preg_match(self::REGEX_CF, $value);
    }

    protected function checkDigit($cf)
    {
        $check = true;

        $s = 0;
        for ($i = 1; $i <= 13; $i += 2)
        {
            $c = $cf[$i];
            if ('0' <= $c && $c <= '9')
                $s += ord($c) - ord('0');
            else
                $s += ord($c) - ord('A');
        }
        for ($i = 0; $i <= 14; $i += 2)
        {
            $c = $cf[$i];
            switch ($c)
            {
                case '0': $s += 1;
                break;
                case '1': $s += 0;
                break;
                case '2': $s += 5;
                break;
                case '3': $s += 7;
                break;
                case '4': $s += 9;
                break;
                case '5': $s += 13;
                break;
                case '6': $s += 15;
                break;
                case '7': $s += 17;
                break;
                case '8': $s += 19;
                break;
                case '9': $s += 21;
                break;
                case 'A': $s += 1;
                break;
                case 'B': $s += 0;
                break;
                case 'C': $s += 5;
                break;
                case 'D': $s += 7;
                break;
                case 'E': $s += 9;
                break;
                case 'F': $s += 13;
                break;
                case 'G': $s += 15;
                break;
                case 'H': $s += 17;
                break;
                case 'I': $s += 19;
                break;
                case 'J': $s += 21;
                break;
                case 'K': $s += 2;
                break;
                case 'L': $s += 4;
                break;
                case 'M': $s += 18;
                break;
                case 'N': $s += 20;
                break;
                case 'O': $s += 11;
                break;
                case 'P': $s += 3;
                break;
                case 'Q': $s += 6;
                break;
                case 'R': $s += 8;
                break;
                case 'S': $s += 12;
                break;
                case 'T': $s += 14;
                break;
                case 'U': $s += 16;
                break;
                case 'V': $s += 10;
                break;
                case 'W': $s += 22;
                break;
                case 'X': $s += 25;
                break;
                case 'Y': $s += 24;
                break;
                case 'Z': $s += 23;
                break;
            }
        }
        if (chr($s % 26 + ord('A')) != $cf[15])
        {
            $check = false;
        }

        return $check;
    }
}