生成crc32表

crc32_table.lua

--[[
-- polynomial: 0x104c11db7
-- 根据MSB-first的crc polynomial，生成单字节表
-- http://en.wikipedia.org/wiki/Cyclic_redundancy_check
-- http://www.cnblogs.com/esestt/archive/2007/08/09/848856.html
-- 这个算法对于crc64应该也是一样的
--]]

local polynomial = 0x04c11db7
local length     = 32

local t = {}
for i=0, length-1 do
    t[i] = bit32.lshift(polynomial, i)
end

local t1 = {}
for i=length-1, 0, -1 do
    t1[length-i] = bit32.extract(polynomial, i, length - i)
end

local ret = {}
for i=0, 255 do
    local crc = 0
    local g   = i
    for j=7,0,-1 do
        if g == 0 then
            break
        end
        if bit32.extract(g, j, 1) == 1 then
            g = bit32.replace(g, 0, j, 1)
            if j > 0 then
                g = bit32.bxor(g, t1[j])
            end
            crc = bit32.bxor(crc, t[j])
        end
    end
    table.insert(ret, crc)
end

for i=1,#ret do
    print(i, string.format("0x%08x", ret[i]))
end