Damm Algorithm

damm.rb

module Damm
  # See http://en.wikipedia.org/wiki/Damm_algorithm
  TABLE=["0317598642","7092154863","4206871359","1750983426","6123045978",
         "3674209581","5869720134","8945362017","9438617205","2581436790"]
  
  def lookup number
    number.to_s.each_char.inject(0) do |m,v|
      TABLE[m][v.to_i].to_i
    end
  end

  def check number
    lookup(number.to_i / 10) == number % 10
  end

  def generate number
    number.to_i * 10 + lookup(number.to_i)
  end

  extend(Damm)
end