/**
* Luhn algorithm
*
* @see http://en.wikipedia.org/wiki/Luhn_algorithm
* @return boolean Success
* @access protected
*/
function _luhn()
{
$_this =& WPToolset_Cake_Validation::getInstance();
if ($_this->deep !== true) {
return true;
}
if ($_this->check == 0) {
return false;
}
$sum = 0;
$length = strlen($_this->check);
for ($position = 1 - $length % 2; $position < $length; $position += 2) {
$sum += $_this->check[$position];
}
for ($position = $length % 2; $position < $length; $position += 2) {
$number = $_this->check[$position] * 2;
$sum += $number < 10 ? $number : $number - 9;
}
return $sum % 10 == 0;
}