信用卡 PHP通过Luhn算法校验信用卡卡号是否有效

$numbers = "49927398716 49927398717 1234567812345678 1234567812345670";
foreach (split(' ', $numbers) as $n)
    echo "$n is ", luhnTest($n) ? 'valid' : 'not valid', '</br>';

function luhnTest($num) {
    $len = strlen($num);
    for ($i = $len-1; $i >= 0; $i--) {
        $ord = ord($num[$i]);
        if (($len - 1) & $i) {
            $sum += $ord;
        } else {
            $sum += $ord / 5 + (2 * $ord) % 10;
        }
    }       
    return $sum % 10 == 0;
}

                                运行结果

49927398716 is valid
49927398717 is not valid
1234567812345678 is not valid
1234567812345670 is valid

                                下面是一个更为简洁的代码

function luhn_test($num) {
    $str = '';
    foreach( array_reverse( str_split( $num ) ) as $i => $c ) $str .= ($i % 2 ? $c * 2 : $c );
    return array_sum( str_split($str) ) % 10 == 0;
}

foreach (array('49927398716','49927398717','1234567812345678','1234567812345670') as $n)
    echo "$n is ", luhn_test($n) ? 'valid' : 'not valid', "</br>\n";

                                输出结果如下

49927398716 is valid
49927398717 is not valid
1234567812345678 is not valid
1234567812345670 is valid