Module:Crc32lua

--[[

LUA MODULE

 digest.crc32 - CRC-32 checksum implemented entirely in Lua.

SYNOPSIS

 local CRC = require 'digest.crc32lua'
 print(CRC.crc32 'test') --> 0xD87F7E0C or -662733300
 
 assert(CRC.crc32('st', CRC.crc32('te')) == CRC.crc32 'test')
 

DESCRIPTION

 This can be used to compute CRC-32 checksums on strings.
 This is similar to [1-2].

API

 Note: in the functions below, checksums are 32-bit integers stored in
 numbers.  The number format currently depends on the bit
 implementation--see DESIGN NOTES below.

 CRC.crc32_byte(byte [, crc]) --> rcrc
 
   Returns CRC-32 checksum `rcrc` of byte `byte` (number 0..255) appended to
   a string with CRC-32 checksum `crc`.  `crc` defaults to 0 (empty string)
   if omitted.

 CRC.crc32_string(s, crc) --> bcrc

   Returns CRC-32 checksum `rcrc` of string `s` appended to
   a string with CRC-32 checksum `crc`.  `crc` defaults to 0 (empty string)
   if omitted.
 
 CRC.crc32(o, crc) --> bcrc

   This invokes `crc32_byte` if `o` is a byte or `crc32_string` if `o`
   is a string.
 
 CRC.bit

   This contains the underlying bit library used by the module.  It
   should be considered a read-only copy.

DESIGN NOTES

 Currently, this module exposes the underlying bit array implementation in CRC
 checksums returned.  In BitOp, bit arrays are 32-bit signed integer numbers
 (may be negative).  In Lua 5.2 'bit32' and 'bit.numberlua', bit arrays are
 32-bit unsigned integer numbers (non-negative).  This is subject to change
 in the future but is currently done due to (unconfirmed) performance
 implications.
 
 On platforms with 64-bit numbers, one way to normalize CRC
 checksums to be unsigned is to do `crcvalue % 2^32`,
 
 The name of this module is inspired by Perl `Digest::CRC*`.

DEPENDENCIES

 Requires one of the following bit libraries:

   BitOp "bit" -- bitop.luajit.org -- This is included in LuaJIT and also available
     for Lua 5.1/5.2.  This provides the fastest performance in LuaJIT.
   Lua 5.2 "bit32" -- www.lua.org/manual/5.2 -- This is provided in Lua 5.2
     and is preferred in 5.2 (unless "bit" also happens to be installed).
   "bit.numberlua" (>=000.003) -- https://github.com/davidm/lua-bit-numberlua
     This is slowest and used as a last resort.
     It is only a few times slower than "bit32" though.

DOWNLOAD/INSTALLATION

 If using LuaRocks:
   luarocks install lua-digest-crc32lua

 Otherwise, download <https://github.com/davidm/lua-digest-crc32lua/zipball/master>.
 Alternately, if using git:
   git clone git://github.com/davidm/lua-digest-crc32lua.git
   cd lua-digest-crc32lua
 Optionally unpack:
   ./util.mk
 or unpack and install in LuaRocks:
   ./util.mk install 
 

REFERENCES

 [1] http://www.axlradius.com/freestuff/CRC32.java
 [2] http://www.gamedev.net/reference/articles/article1941.asp
 [3] http://java.sun.com/j2se/1.5.0/docs/api/java/util/zip/CRC32.html
 [4] http://www.dsource.org/projects/tango/docs/current/tango.io.digest.Crc32.html
 [5] http://pydoc.org/1.5.2/zlib.html#-crc32
 [6] http://www.python.org/doc/2.5.2/lib/module-binascii.html

LICENSE

 (c) 2008-2011 David Manura.  Licensed under the same terms as Lua (MIT).

 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:

 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 (end license)

--]]

local M = {_TYPE='module', _NAME='digest.crc32', _VERSION='0.3.20111128'}

local type = type local require = require local setmetatable = setmetatable

--[[

Requires the first module listed that exists, else raises like `require`.
If a non-string is encountered, it is returned.
Second return value is module name loaded (or ).
--]]

local function requireany(...)

 local errs = {}
 for _,name in ipairs{...} do
   if type(name) ~= 'string' then return name,  end
   local ok, mod = pcall(require, name)
   if ok then return mod, name end
   errs[#errs+1] = mod
 end
 error(table.concat(errs, '\n'), 2)

end

local bit, name_ = requireany('bit32', 'bit', 'bit.numberlua') local bxor = bit.bxor local bnot = bit.bnot local band = bit.band local rshift = bit.rshift

-- CRC-32-IEEE 802.3 (V.42) local POLY = 0xEDB88320

-- Memoize function pattern (like http://lua-users.org/wiki/FuncTables ). local function memoize(f)

 local mt = {}
 local t = setmetatable({}, mt)
 function mt:__index(k)
   local v = f(k); t[k] = v
   return v
 end
 return t

end

-- CRC table. local crc_table = memoize(function(i)

 local crc = i
 for _=1,8 do
   local b = band(crc, 1)
   crc = rshift(crc, 1)
   if b == 1 then crc = bxor(crc, POLY) end
 end
 return crc

end)

function M.crc32_byte(byte, crc)

 crc = bnot(crc or 0)
 local v1 = rshift(crc, 8)
 local v2 = crc_table[bxor(crc % 256, byte)]
 return bnot(bxor(v1, v2))

end local M_crc32_byte = M.crc32_byte

function M.crc32_string(s, crc)

 crc = crc or 0
 for i=1,#s do
   crc = M_crc32_byte(s:byte(i), crc)
 end
 return crc

end local M_crc32_string = M.crc32_string

function M.crc32(s, crc)

 if type(s) == 'string' then
   return M_crc32_string(s, crc)
 else
   return M_crc32_byte(s, crc)
 end

end

M.bit = bit -- bit library used

return M