--Copyright (c) 2007-2008 Neil Richardson (nrich@iinet.net.au)
--
--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.
local max = 2^32 -1

local CRC32 = {
    0,79764919,159529838,222504665,319059676,
    398814059,445009330,507990021,638119352,
    583659535,797628118,726387553,890018660,
    835552979,1015980042,944750013,1276238704,
    1221641927,1167319070,1095957929,1595256236,
    1540665371,1452775106,1381403509,1780037320,
    1859660671,1671105958,1733955601,2031960084,
    2111593891,1889500026,1952343757,2552477408,
    2632100695,2443283854,2506133561,2334638140,
    2414271883,2191915858,2254759653,3190512472,
    3135915759,3081330742,3009969537,2905550212,
    2850959411,2762807018,2691435357,3560074640,
    3505614887,3719321342,3648080713,3342211916,
    3287746299,3467911202,3396681109,4063920168,
    4143685023,4223187782,4286162673,3779000052,
    3858754371,3904687514,3967668269,881225847,
    809987520,1023691545,969234094,662832811,
    591600412,771767749,717299826,311336399,
    374308984,453813921,533576470,25881363,
    88864420,134795389,214552010,2023205639,
    2086057648,1897238633,1976864222,1804852699,
    1867694188,1645340341,1724971778,1587496639,
    1516133128,1461550545,1406951526,1302016099,
    1230646740,1142491917,1087903418,2896545431,
    2825181984,2770861561,2716262478,3215044683,
    3143675388,3055782693,3001194130,2326604591,
    2389456536,2200899649,2280525302,2578013683,
    2640855108,2418763421,2498394922,3769900519,
    3832873040,3912640137,3992402750,4088425275,
    4151408268,4197601365,4277358050,3334271071,
    3263032808,3476998961,3422541446,3585640067,
    3514407732,3694837229,3640369242,1762451694,
    1842216281,1619975040,1682949687,2047383090,
    2127137669,1938468188,2001449195,1325665622,
    1271206113,1183200824,1111960463,1543535498,
    1489069629,1434599652,1363369299,622672798,
    568075817,748617968,677256519,907627842,
    853037301,1067152940,995781531,51762726,
    131386257,177728840,240578815,269590778,
    349224269,429104020,491947555,4046411278,
    4126034873,4172115296,4234965207,3794477266,
    3874110821,3953728444,4016571915,3609705398,
    3555108353,3735388376,3664026991,3290680682,
    3236090077,3449943556,3378572211,3174993278,
    3120533705,3032266256,2961025959,2923101090,
    2868635157,2813903052,2742672763,2604032198,
    2683796849,2461293480,2524268063,2284983834,
    2364738477,2175806836,2238787779,1569362073,
    1498123566,1409854455,1355396672,1317987909,
    1246755826,1192025387,1137557660,2072149281,
    2135122070,1912620623,1992383480,1753615357,
    1816598090,1627664531,1707420964,295390185,
    358241886,404320391,483945776,43990325,
    106832002,186451547,266083308,932423249,
    861060070,1041341759,986742920,613929101,
    542559546,756411363,701822548,3316196985,
    3244833742,3425377559,3370778784,3601682597,
    3530312978,3744426955,3689838204,3819031489,
    3881883254,3928223919,4007849240,4037393693,
    4100235434,4180117107,4259748804,2310601993,
    233574846,2151335527,2231098320,2596047829,
    2659030626,2470359227,2550115596,2947551409,
    2876312838,2788305887,2733848168,3165939309,
    3094707162,3040238851,2985771188,
}

local function xor(a, b)
    local calc = 0    

    for i = 32, 0, -1 do
	local val = 2 ^ i
	local aa = false
	local bb = false

	if a == 0 then
	    calc = calc + b
	    break
	end

	if b == 0 then
	    calc = calc + a
	    break
	end

	if a >= val then
	    aa = true
	    a = a - val
	end

	if b >= val then
	    bb = true
	    b = b - val
	end

	if not (aa and bb) and (aa or bb) then
	    calc = calc + val
	end
    end

    return calc
end

local function lshift(num, left)
    local res = num * (2 ^ left)
    return res % (2 ^ 32)
end

local function rshift(num, right)
    local res = num / (2 ^ right)
    return math.floor(res)
end

local function crc32(str)
    local count = string.len(tostring(str))
    local crc = max
    
    local i = 1
    while count > 0 do
	local byte = string.byte(str, i)

	crc = xor(lshift(crc, 8), CRC32[xor(rshift(crc, 24), byte) + 1])

	i = i + 1
	count = count - 1
    end

    return crc
end

return crc32

--
-- CRC32.lua
--
-- A pure Lua implementation of a CRC32 hashing algorithm. Slower than using a C implemtation,
-- but useful having no other dependencies.
--
--
-- Synopsis
--
-- require('CRC32')
--
-- crchash = CRC32.Hash('a string')
--
-- Methods:
--
-- hashval = CRC32.Hash(val)
--    Calculates and returns (as an integer) the CRC32 hash of the parameter 'val'.