Luhnアルゴリズムの実装サンプル

gistfile1.rb

module Luhn
  CODE_0 = "0".ord
  CODE_9 = "9".ord
  CODE_A = "A".ord
  CODE_Z = "Z".ord

  def self.add(data)
    return data + get_char(data)
  end

  def self.check(data)
    return (calculate(data) % 10) == 0
  end

  def self.get_char(data)
    return ((10 - (calculate(data + "0") % 10)) % 10).to_s
  end

  private
  def self.calculate(data)
    sum = 0
    flag = (data.length % 2 == 0)
    data.each_byte.with_index do |ch, i|
      if CODE_0 <= ch && ch <= CODE_9
        num = ch - CODE_0
      elsif CODE_A <= ch && ch <= CODE_Z
        num = ch - CODE_A + 10
      else
        raise ArgumentError
      end
      num *= 2 if flag
      if num > 9
        num = (num % 10) + (num / 10)
      end
      sum += num
      flag = !flag
    end
    return sum
  end
end