Dahnielson

I just finished implementing the Verhoeff checksum algorithm in PHP, you can download it as verhoeff.zip. Yes, mathematically it’s a bit more elaborate than other checksum algorithms, but with look-up tables it’s fairly simple and lightweight.

The implementation provides two functions calcsum($number) and checksum($number). The first one return a check digit for the decimal number used as argument, just append the returned digit to the number and you got yourself a checkable number. The second function checks the number (including the appended check digit) used as argument, the number is only valid if the function return zero.

I noticed a small bug due to a misplace modulus (simple PHP syntax typo), the verhoeff.php is now updated, tested and in working order. The bug only affected the calculation of check digits, not the check function.