<?php
/* luhn_checker(): This is a small PHP function for checking valid *
 * credit card with LUHN algorithm                                  *
 *                                                                  *
 * Last updated: 26 August 2007                                     *
 * This is a free PHP script under GNU GPL version 2.0 or above     *
 * Copyright (C) 2007 Sam Tang                                      *
 * Feedback/comment/suggestions : http://www.real-blog.com/        */

function luhn_checker($card_num){
	// 將非數字的字串移除
	$card_num = preg_replace("/\D|\s/", "", $card_num);

	$sum = 0;
	for($i=0; $i<strlen($card_num); $i++){
		$digit = substr($card_num, $i, 1);
		if(($i % 2) == 0){
			// 在單數位置的數值乘 2
			$digit = $digit * 2;
		}

		if ($digit > 9)	$digit = $digit - 9;
		$sum += $digit;
	}

	if(($sum % 10) == 0 && strlen($card_num) == 16){
		return TRUE;
	}else{
		return FALSE;
	}
}

/* Example
if(luhn_checker("1234567812345678")){
	echo "Correct!";
}else{
	echo "Wrong card number!";
}
*/
?>