--Copyright (c) 2007-2008 Neil Richardson (nrich@iinet.net.au)
--Copyright (c) 2011 Lance Li <lancelijade@gmail.com> 
--
--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.

--[[
crc32.lua

A pure Lua implementation of a CRC32 hashing algorithm. Slower than using a C implemtation,
but useful having no other dependancies.

This module is based on Neil Richardson's implementation 
http://luamemcached.googlecode.com/svn/trunk/CRC32.lua

Changelog by Lance:

depended on LuaJit's bitop module,
rebuileded table by using poly 0xEDB88320, 
program little rewrited 

Synopsis

local crc32 = 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'. 
--]]

local string = require("string")
local bit = require("bit")
local tostring = tostring

module('crc32')

local CRC32 = {
    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 
    0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3, 
    0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 
    0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 
    0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 
    0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 
    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 
    0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5, 
    0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, 
    0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 
    0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 
    0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 
    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 
    0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f, 
    0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 
    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 
    0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, 
    0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433, 
    0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 
    0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01, 
    0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 
    0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 
    0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c, 
    0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65, 
    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 
    0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 
    0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, 
    0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 
    0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 
    0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, 
    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 
    0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 
    0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, 
    0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 
    0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 
    0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 
    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 
    0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7, 
    0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, 
    0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 
    0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 
    0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 
    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 
    0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79, 
    0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 
    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 
    0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 
    0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d, 
    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 
    0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, 
    0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 
    0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 
    0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e, 
    0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777, 
    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 
    0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 
    0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 
    0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 
    0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 
    0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, 
    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 
    0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf, 
    0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, 
    0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
}

local xor = bit.bxor
local lshift = bit.lshift
local rshift = bit.rshift
local band = bit.band

function hash(str)
    str = tostring(str)
    local count = string.len(str)
    local crc = 2 ^ 32 - 1 
    local i = 1

    while count > 0 do
        local byte = string.byte(str, i)
        crc = xor(rshift(crc, 8), CRC32[xor(band(crc, 0xFF), byte) + 1])
        i = i + 1
        count = count - 1
    end
    crc = xor(crc, 0xFFFFFFFF)
    -- dirty hack for bitop return number < 0
    if crc < 0 then crc = crc + 2 ^ 32 end 

    return crc
end

--[[
-- the previous one is equvilent to this function but faster 
function hash_s(str)

    local i = 1
    local crc = 2 ^ 32 - 1
    local poly = 0xEDB88320

    for k = string.len(str), 1, -1 do
        local byte = string.byte(str, i)
        crc = bit.bxor(crc, byte)
        for j = 0, 7 do
            if bit.band(crc, 1) ~= 0 then
                crc = bit.bxor(bit.rshift(crc, 1), poly)
            else
                crc = bit.rshift(crc, 1)
            end
        end
        i = i + 1
    end
    crc = bit.xor(crc, 0xFFFFFFFF)
    if crc < 0 then crc = crc + 2 ^ 32 end

    return crc
end
--]]

