base32.rb

gistfile1.rb

module Base32
  TABLE = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567".downcase

  class Chunk < Struct.new(:bytes)
    def decode
      b = bytes.take_while{|c| c != 61 } # strip padding
      n = (b.length * 5.0 / 8.0).floor
      p = b.length < 8 ? 5 - (n * 8) % 5 : 0
      c = b.inject(0){|m,o| (m << 5) + TABLE.index(o.chr) } >> p
      (0...n).to_a.reverse.map{|i| ((c >> i * 8) & 0xff).chr }
    end

    def encode
      n = (bytes.length * 8.0 / 5.0).ceil
      p = n < 8 ? 5 - (bytes.length * 8) % 5 : 0
      c = bytes.inject(0){|m,o| (m << 8) + o } << p
      [(0...n).to_a.reverse.map{|i| TABLE[(c >> i * 5) & 0x1f].chr }, ("=" * (8-n))]
    end
  end

  def self.chunks(str, size);
    str.bytes.each_slice(size).map{|i| Chunk.new(i) }
  end

  def self.encode(str); chunks(str, 5).map(&:encode).flatten.join; end
  def self.decode(str); chunks(str, 8).map(&:decode).flatten.join; end
end

p Base32.encode( Base32.decode("rc3no6ludp4ozphw") ) == "rc3no6ludp4ozphw"