Helper classes to calculate and validate ckecksums

Install using composer. Exists as byrokrat/checkdigit in the packagist repository.

composer require byrokrat/checkdigit

The Calculator interface defines two methods:

• isValid(string $number) : bool checks if number contains a valid check digit.
• calculateCheckDigit(string $number) : string calculates the check digit for number.

Implementations include:

• Modulo10 and Luhn for modulo 10 check digits (Luhn is simply a shorthand for Modulo10).
• Modulo11 for modulo 11 check digits.
• Modulo97 for modulo 97 check digits.

use byrokrat\checkdigit\Luhn;
$luhn = new Luhn();
$luhn->isValid('55555551');            // true
$luhn->isValid('55555550');            // false
$luhn->calculateCheckDigit('5555555'); // '1'

Checkdigit is covered under the WTFPL.

@author Hannes Forsgård (hannes.forsgard@fripost.org)