Check if card number passes Luhn Check

check-credit-card-luhn-is-valid.php

/**
* Determines whether the supplied PAN is valid. Will also check to see whether the PAN is numeric.
* @private
* @param pan
*	The PAN to validate.
* @return If the PAN failed the Luhn Check of if the PAN is not numeric.
*/
public function isValidLuhn($pan) {

	if (!ctype_digit((string)$pan)) {
		return false;
	}

	$nSum = 0;
	for ($nPos = strlen($pan) - 1, $nMultiple = 0; $nPos >= 0; $nPos--, $nMultiple ^= 1) {
		$nProduct = $pan{$nPos} * ($nMultiple + 1);
		$nSum += (($nProduct > 9) ? $nProduct - 9 : $nProduct);
	}
	return (($nSum % 10) === 0);
}