From: snacktime <snacktime@...>
Date: 2006-08-13T15:23:37+09:00
Subject: Re: string parity module

If anyone has any input on how to write this better or a better way to
implement it let me know.  In any case here is a class for setting
odd/even/space parity on strings.

class StringParity

  def initialize
    even_bits = "\0"
    odd_bits = "\200"
    codes = ""
    ascii = []

    @even_parity = []
    @odd_parity = []
    @space_parity = []

    8.times do
      even_bits << odd_bits
      odd_bits = even_bits.clone
      odd_bits.tr!("\0\200","\200\0")
    end


    (0..255).collect {|i| ascii << i}
    codes = ascii.pack('C*')
    (0..127).collect { |i| @space_parity[i + 128] = codes[i] }
    @even_parity = (0..codes.length-1).collect { |i| codes[i] ^ even_bits[i] }
    @odd_parity = (0..codes.length-1).collect { |i| codes[i] ^ odd_bits[i] }
  end

  def setEvenParity(str)
    new = []
    str.each_byte {|b| new << @even_parity[b]}
    new.pack("C*")
  end

  def setOddParity(str)
    new = []
    str.each_byte {|b| new << @odd_parity[b]}
    new.pack("C*")
  end

  def setSpaceParity(str)
    new = []
    str = str.unpack("C*")
    str.collect {|b| new << (@space_parity[b] || b)}
    new.pack("C*")
  end

end

s = StringParity.new
str = "testing12345678910()*&^%@!~"

str = s.setEvenParity(str)
print "#{str}\n"

str = s.setSpaceParity(str)
print "#{str}\n"

str = s.setOddParity(str)
print "#{str}\n"

str = s.setSpaceParity(str)
print "#{str}\n"