CheckDigit

Ruby implementation of the Luhn, Damm and Verhoeff check digit algorithms

• is the latest released version
• For the version under development (master), check version.rb

Installation

Add this line to your application's Gemfile:

gem 'check_digit'

And then execute:

$ bundle

Or install it yourself as:

$ gem install check_digit

Usage

Each implementation provides the same 2 class methods:

• checksum(num) - returns a new number with the checksum digit appended at the end
• valid?(num) - returns true if the number has a valid checksum digit, false if the number has an invalid checksum digit

Code sample:

require 'check_digit'

Damm.checksum(123) # returns 1234
Damm.valid?(1234) # returns true
Damm.valid?(1239) # returns false

Algorithm Comparison - Error Prevention

Error Type	% of All Errors	Luhn	Damm	Verhoeff
single errors: a becomes b	60% to 95%	1	1	1
omitting or adding a digit	10% to 20%	1	1	1
adjacent transpositions: ab becomes ba	10% to 20%	2	1	1
twin errors: aa becomes bb	0.5% to 1.5%	3	1	2
jump transpositions: acb becomes bca	0.5% to 1.5%	2	1	2
jump twin errors: aca becomes bcb	below 1%	1	1	2
phonetic errors: a0 becomes 0a	0.5% to 1.5%	1*	1	2

Source: http://www.augustana.ab.ca/~mohrj/algorithms/checkdigit.html

* Not entirely sure if Luhn catches all phonetic errors, e.g. 13 instead of 30

Legend

1. Prevents all errors
2. Prevents most errors
3. Prevents some errors
4. Does not prevent any errors

Algorithm Comparison - Performance

50,000 iterations (time in seconds - lower is better)

Algorithm	Generate	Validate
Luhn	5.163268	5.085513
Damm	1.001179	0.996764
Verhoeff	2.496255	2.471240

* Test was on Linux 16.04 with 2.80GHz Intel Xeon E5-1603 using Ruby 2.4.1

Contributing

1. Fork it ( https://github.com/elitwin/check_digit/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Attributions

The Verhoeff implementation was provided from this repo (https://github.com/bai/verhoeff) and was the inspiration for the interface (checksum, valid?) used by all the implementations