failsafe32.rb

class HammingCode
  attr_reader :data_bits
  def initialize(number)
    @number = number
    @data_bits = number.to_s(2)
  end
  
  def parity_bits
    indexes = []
    current_index = 3
    @data_bits.split(//).reverse.each do |b|
      current_index += 1 if (current_index & (current_index - 1)) == 0
      indexes << current_index if b == '1'
      current_index += 1
    end
    indexes.inject(:^).to_s(2)
  end
  
  def word
    pb = parity_bits.split(//).reverse
    db = @data_bits.dup.split(//).reverse
    
    output = [pb.shift, pb.shift]
    until db.length == 0 && pb.length == 0
      if (output.length + 1 & (output.length)) == 0
        output << pb.shift
      else
        output << db.shift
      end
    end
    output.reverse.join
  end
end

module FailSafeBase32
  extend self
  Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
  
  def convert(num)
    output_number = ""
    number = HammingCode.new(num).word.to_i(2)
    
    while number >= 32
      r = number % 32
      output_number = Alphabet[r] + output_number
      number /= 32
    end
    
    output_number = Alphabet[number] + output_number
    output_number
  end
end


require 'test/unit'
class TestHamming < Test::Unit::TestCase
  Test = HammingCode.new(1301)

  def test_word
    assert_equal Test.word, "101000110101110"
  end
  
  def test_parity_bits
    assert_equal Test.parity_bits, "1110"
  end
  
  def test_data_bits
    assert_equal Test.data_bits, 1301.to_s(2)
  end
end