Generating Luhn Checksums

Question

There are lots of implementations for validating Luhn checksums but very few for generating them. I\'ve come across this one however in my tests it has revealed to be buggy

Answer 1

This is a function that could help you, it's short and it works just fine.

function isLuhnValid($number)
{
    if (empty($number))
        return false;

    $_j = 0;
    $_base = str_split($number);
    $_sum = array_pop($_base);
    while (($_actual = array_pop($_base)) !== null) {
        if ($_j % 2 == 0) {
            $_actual *= 2;
            if ($_actual > 9)
                $_actual -= 9;
        }
        $_j++;
        $_sum += $_actual;
    }
    return $_sum % 10 === 0;
}