Ruby class implementing H. Michael Damm's check digit algorithm

damm_algorithm.rb

class DammAlgorithm
  # http://en.wikipedia.org/wiki/Damm_algorithm

  TABLE = [ [0, 7, 4, 1, 6, 3, 5, 8, 9, 2],
            [3, 0, 2, 7, 1, 6, 8, 9, 4, 5],
            [1, 9, 0, 5, 2, 7, 6, 4, 3, 8],
            [7, 2, 6, 0, 3, 4, 9, 5, 8, 1],
            [5, 1, 8, 9, 0, 2, 7, 3, 6, 4],
            [9, 5, 7, 8, 4, 0, 2, 6, 1, 3],
            [8, 4, 1, 3, 5, 9, 0, 2, 7, 6],
            [6, 8, 3, 4, 9, 5, 1, 0, 2, 7],
            [4, 6, 5, 2, 7, 8, 3, 1, 0, 9],
            [2, 3, 9, 6, 8, 1, 4, 7, 5, 0]
          ]

  def self.calculate_digit(str_or_int)
    interim_digit = 0
    digits(str_or_int).each do |digit|
      interim_digit = TABLE[digit][interim_digit]
    end
    interim_digit
  end

  def self.calculate(str_or_int)
    with_check_digit = str_or_int.to_i * 10 + calculate_digit(str_or_int)
    str_or_int.kind_of?(Integer) ?  with_check_digit : with_check_digit.to_s.rjust(str_or_int.length + 1, '0')
  end

  def self.validate(str_or_int)
    calculate_digit(str_or_int) == 0
  end

  private

  def self.digits(str_or_int)
    str_or_int.to_s.gsub(/\D/, '').sub(/^0+/, '').to_s.chars.map {|c| c.to_i}
  end
end