LUHN

Arduino Library for calculating LUHN checksum.

Description

The LUHN algorithm is a checksum (a.k.a. mod 10) invented by Hans Peter Luhn in 1960. It is used to validate a variety of product ID's to detect typing errors an/of digit swaps. So it is not to secure a number but to prevent common mistakes when entering a code in a system. The LUHN check uses very few resources and is pretty fast.

Basic idea is to put all digits-1 through the formula and the output should equal the last digit.

Note: some LUHN validations uses the reversed product string.

https://en.wikipedia.org/wiki/Luhn_algorithm

Interface

#include "LUHN.h"

LUHN() constructor
bool isValid(char * buffer ) validates the code in the parameter buffer. The parameter buffer is a '\0' terminated char array. Length should be less than 254.
bool isValid(const char * buffer ) idem.
char generateChecksum(char * buffer) Returns the char '0'..'9' which is the checksum of the code in the parameter buffer. The parameter buffer is a '\0' terminated char array. Length should be less than 254.
bool generate(char * buffer, uint8_t length, char * prefix) Generates a char array including LUHN number with a defined prefix of max length. Returns false if the prefix exceeds length -1.

Stream

char add(char c) add char, return LUHN so far.
char reset() return last LUHN.

The internal counter for the stream interface is 16 bit. This limits the nr of add() calls to about 65530. (if this is a problem, make it an uinit32_t)

Future

must

update documentation

should

unit tests
look for optimization

could

uint32_t interface for up to 8 digit ID's (99.999.999)
- isValid(uint32_t)
- generateChecksum(uint32_t)
- how about leading zero's

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