Luhn's algorithm in php

gistfile1.aw

<?php
function is_valid_luhn($number) {
  settype($number, 'string');
  $sumTable = array(
    array(0,1,2,3,4,5,6,7,8,9),
    array(0,2,4,6,8,1,3,5,7,9));
  $sum = 0;
  $flip = 0;
  for ($i = strlen($number) - 1; $i >= 0; $i--) {
    $sum += $sumTable[$flip++ & 0x1][$number[$i]];
  }
  return $sum % 10 === 0;
}

9) { $val -=9; } $sum += $val; } return(($sum % 10) == 0); } if (! is_valid_nums($_POST['nums'])) { echo 'the num is invalid.'; } } ?>

Please be aware that this functions will only work if the passed argument is a string, else it will fail.
For more info read:

http://lamp-ios.com/?p=256

It has to do with 1 thing:

1. Your platform (32 or 64 bit)

Be aware of this

Here is a simple implementation:

/**
 * @see http://en.wikipedia.org/wiki/Luhn_algorithm
 */
private function checksum ($card_number) {
    $card_number_checksum = '';

    foreach (str_split(strrev((string) $card_number)) as $i => $d) {
        $card_number_checksum .= $i %2 !== 0 ? $d * 2 : $d;
    }

    return array_sum(str_split($card_number_checksum)) % 10 === 0;
}

You can simply typecast whatever input you have into a string before applying it to the function or you could incorporate a step to first typecast your arguments into strings.

This function works perfectly if your number is already in a 16-character string, is_valid_luhn("4111111111111111")

But the function will fail if the string contains any symbols or spaces, is_valid_luhn("4111 1111 1111 1111") = false

This can be easily fixed by placing a preg_replace at the beginning of the function to strip all non-digit characters.

$number = preg_replace("/[^0-9]/", "", $number);

PHP:

function isValid($num) {
    $num = preg_replace('/[^\d]/', '', $num);
    $sum = '';

    for ($i = strlen($num) - 1; $i >= 0; -- $i) {
        $sum .= $i & 1 ? $num[$i] : $num[$i] * 2;
    }

    return array_sum(str_split($sum)) % 10 === 0;
}

Javascript:

function isValid(number) {
    var num = number.replace(/[^\d]/, '');
    var str = '';

    for (var i = num.length - 1; i >= 0; -- i) {
        str += i & 1 ? num[i] : (parseInt(num[i]) * 2).toString();
    }

    var sum = str.split('').reduce(function(prev, current) {
        return prev + parseInt(current);
    }, 0);

    return sum % 10 === 0;
};

= 0; $i--) { $sum += $sumTable[$flip++ & 0x1][$number[$i]]; } return $sum % 10 === 0; }

        //Using Luhn's algorithm to validate a credit card

        public static function isValidCardNumber($number){
        	settype($number, 'string');
        	$number = preg_replace("/[^0-9]/", "", $number);
        	$numberChecksum= '';
		$reversedNumberArray = str_split(strrev($number));
		foreach ($reversedNumberArray as $i => $d) {
		    $numberChecksum.= (($i % 2) !== 0) ? (string)((int)$d * 2) : $d;
		}
		$sum = array_sum(str_split($numberChecksum));
                return ($sum % 10) === 0;
        }

is there any possibility to get bpay biller address and info by biller code?

@mikemirten first I thought thats really small and simple to understand but unfortunately it's wrong. have you tried this with a credit card number of odd length? visas can have 13 - 16 numbers and that fails.

my solution is now:

function validateLuhn(string $number): bool
{
    $sum = 0;
    $revNumber = strrev($number);
    $len = strlen($number);

    for ($i = 0; $i < $len; $i++) {
        $sum += $i & 1 ? ($revNumber[$i] > 4 ? $revNumber[$i] * 2 - 9 : $revNumber[$i] * 2) : $revNumber[$i];
    }

    return $sum % 10 === 0;
}

@mogzol: you are right: the string sum does not make sense... So I removed it.

edit fixed the calculation without string split and unused variables

Alternative version of @tflori's code that doesn't rely on strrev, array_sum or str_split, which makes it more readable IMO, and slightly faster (though at this point it's basically just the original code without the sum table):

function validateLuhn(string $number): bool
{
    $sum = 0;
    $flag = 0;

    for ($i = strlen($number) - 1; $i >= 0; $i--) {
        $add = $flag++ & 1 ? $number[$i] * 2 : $number[$i];
        $sum += $add > 9 ? $add - 9 : $add;
    }

    return $sum % 10 === 0;
}

@tflori Your updated code doesn't work just FYI. You actually did need the array_sum. This is because of the first step outlined here: https://en.wikipedia.org/wiki/Luhn_algorithm#Description

If the result of this doubling operation is greater than 9 (e.g., 8 × 2 = 16), then add the digits of the result (e.g., 16: 1 + 6 = 7, 18: 1 + 8 = 9)

Your original code achieved this by using a string and summing all the numbers in the string. My code uses the alternate method mentioned:

alternatively, the same final result can be found by subtracting 9 from that result (e.g., 16: 16 − 9 = 7, 18: 18 − 9 = 9)

But your newly edited code does neither, and as such returns false for many valid numbers.

@mogzol ah f**k.. thanks for the info 👍