Damm validation & generation code in PHP.Damm algorithm is a check digit algorithm that detects all single-digit errors and all adjacent transposition errors.

damm_check_digit.php

<?php
/**
 * The Damm check digit
 * For more information cf. http://en.wikipedia.org/wiki/Damm_algorithm
 * totally anti-symmetric quasigroup
 *
 * @author Wuri Nugrahadi <[email protected]>
 */
if (! function_exists('taq'))
{
	function taq($digits)
	{
		$taq_table = array(
			'0317598642', '7092154863', '4206871359', '1750983426', '6123045978',
			'3674209581', '5869720134', '8945362017', '9438617205', '2581436790');
		$interim = 0;

		foreach (str_split($digits) as $digit) {
			if (! preg_match('~\d~', $digit))
			{
				return FALSE;
			}
			$interim = substr($taq_table[$interim], $digit, 1);
		}

		return $interim;
	}
}

if (! function_exists('calc_check_digit'))
{
	function calc_check_digit($digits)
	{		
		return $digits.taq($digits);
	}
}

if (! function_exists('is_check_digit_valid'))
{
	function is_check_digit_valid($digits)
	{
		return taq($digits) == 0;
	}
}