Luhn_algorithms.php

<?
// Old Code
function CheckCC($field, $msg)
{
    $Name = 'n/a';
    $Num  = $this->_getValue($field);

    //  Innocent until proven guilty
    $GoodCard = true;

    //  Get rid of any non-digits
    $Num = preg_replace("/[^[:digit:]]/", "", $Num);

    //  Perform card-specific checks, if applicable
    switch ($Name)
    {
        case "mcd" :
            $GoodCard = ereg("^5[1-5].{14}$", $Num);
            break;

        case "vis" :
            $GoodCard = ereg("^4.{15}$|^4.{12}$", $Num);
            break;

        case "amx" :
            $GoodCard = ereg("^3[47].{13}$", $Num);
            break;

        case "dsc" :
            $GoodCard = ereg("^6011.{12}$", $Num);
            break;

        case "dnc" :
            $GoodCard = ereg("^30[0-5].{11}$|^3[68].{12}$", $Num);
            break;

        case "jcb" :
            $GoodCard = ereg("^3.{15}$|^2131|1800.{11}$", $Num);
            break;
    }

    //  The Luhn formula works right to left, so reverse the number.
    $Num = strrev($Num);

    $Total = 0;

    $str_len = strlen($Num);

    for ($x=0; $x<$str_len; $x++)
    {
        $digit = substr($Num,$x,1);

        // If it's an odd digit, double it
        if ($x/2 != floor($x/2))
        {
            $digit *= 2;

            // If the result is two digits, add them
            if (strlen($digit) == 2)
                $digit = substr($digit,0,1) + substr($digit,1,1);
        }
        // Add the current digit, doubled and added if applicable, to the Total
        $Total += $digit;
    }

    //  If it passed (or bypassed) the card-specific check and the Total is
    //  evenly divisible by 10, it's cool!
    if ($GoodCard && $Total % 10 == 0)
        return true;
    else
    {
        $this->_errorList[] = array("field" => $field, "value" => $Num, "msg" => $msg);
        return false;
    }
}


// New shiny code
/**
 * Check if a Credit Card is valid according to the Luhn Algorithm
 * @see https://en.wikipedia.org/wiki/Luhn_algorithm
 * @see http://rosettacode.org/wiki/Luhn_test_of_credit_card_numbers#PHP
 * @param $field
 * @param $msg
 * @return bool
 */
function CheckCC($field, $msg)
{
    $num = $this->_getValue($field);
    $str = '';
    // Double every other digit
    foreach (array_reverse(str_split($num)) as $index => $digit){
        $str .= $digit * (2 >> ($index % 2));
    }
    // sum the result. If divisible by 10, then it's good!
    if (!array_sum(str_split($str)) % 10 == 0) {
        $this->_errorList[] = array("field" => $field, "value" => $num, "msg" => $msg);
        return false;
    }
    return true;
}