From: "NAKAMURA, Hiroshi" <nakahiro@...>
Date: 2005-07-29T10:46:38+09:00
Subject: Re: Ruby libraries

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Hi,

Andrew Falanga wrote:
> Outstanding!  I forgot to ask in the original post, however, that I also
>  need a library for creating CRC's with a divisor of 32bits.  Does
> something like this exist?

You can use Zlib.crc32 if you need CRC32-Reversed.  And attached is my
port of CRC base functions in Classless.hasher at
http://www.classless.net/projects/hasher/ .  Use this if you need CRC32
- not Reversed.

Regards,
// NaHi

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# crc.rb - Ruby port of CRC.cs in Classless.Hasher - C#/.NET Hash and Checksum Algorithm Library. (http://www.classless.net/projects/hasher/)

=begin
following is an excerpt of CRC.cs in Classless.Hasher.

/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Classless.Hasher - C#/.NET Hash and Checksum Algorithm Library.
 *
 * The Initial Developer of the Original Code is Classless.net.
 * Portions created by the Initial Developer are Copyright (C) 2004 the Initial
 * Developer. All Rights Reserved.
 *
 * Contributor(s):
 *		Jason Simeone (jay@classless.net)
 * 
 * ***** END LICENSE BLOCK ***** */
=end


class CRC
  def initialize(order, poly, iv, xor, reflect)
    @order = order
    @poly = poly
    @iv = iv
    @xor = xor
    @reflect = reflect
    if @reflect
      @mask = (2 ** (@order - 8)) - 1
    end
    @lookup = build_lookup
    @crc = init
  end

  def init
    crc = @iv
    if @reflect
      crc = reflect(crc, @order)
    end
    crc
  end

  def update(str)
    topbit = 1 << (@order - 1)
    widthmask = (topbit << 1) - 1
    str.each_byte do |byte|
      if @reflect
        @crc = ((@crc >> 8) & @mask) ^ @lookup[(@crc ^ byte) & 0xFF]
      else
        @crc = (@crc << 8) ^ @lookup[((@crc >> (@order - 8)) ^ byte) & 0xFF]
      end
      @crc &= widthmask
    end
  end

  def final
    @crc ^= @xor
    bytes = (@order + 7) >> 3
    @crc
  end

private

  def build_lookup
    lookup = []
    topbit = 1 << (@order - 1)
    widthmask = (topbit << 1) - 1
    for idx in 0..255
      v = idx
      v = reflect(v, 8) if @reflect
      v <<= (@order - 8)
      8.times do
        if (v & topbit).nonzero?
          v = (v << 1) ^ @poly
        else
          v <<= 1
        end
      end
      v = reflect(v, @order) if @reflect
      v &= widthmask
      lookup << v
    end
    lookup
  end

  def reflect(crc, bits)
    base = crc
    for idx in 0...bits
      bitmask = 1 << ((bits - 1) - idx)
      if (base & 1).nonzero?
        crc |= bitmask;
      else
        crc &= ~bitmask;
      end
      base >>= 1
    end
    crc
  end
end


if __FILE__ == $0
  crc32 = CRC.new(32, 0xEDB88320, 0xFFFFFFFF, 0xFFFFFFFF, false)
  crc32rev = CRC.new(32, 0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true)
  crc32.update("12345")
  p crc32.final
  crc32rev.update("12345")
  p crc32rev.final

  require 'zlib'
  p Zlib.crc32("12345")

  crc8 = CRC.new(8, 0xE0, 0x00, 0x00, false)
  msg = ARGV.shift
  msg = "\1\2\3\4"
  crc8.update(msg)
  printf("%x\n", crc8.final)

  require 'pgp/util'

  crc24 = CRC.new(24, 0x01864cfb, 0x00b704ce, 0, false)

  msg = ARGV.shift
  crc24.update(msg)
  p crc24.final

  p PGP::Util.crc24(msg)
end

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