CRC

local CRC = {}

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

function CRC.table()
    if CRC._table == nil then
        local tab = {}
        for i = 0, 255 do
            local v = i
            for _ = 1, 8 do
                if v % 2 == 1 then
                    v = xor(0xEDB88320, rshift(v, 1))
                else
                    v = rshift(v, 1)
                end
            end
            tab[i] = v
        end
        CRC._table = tab
    end
    return CRC._table
end

function CRC.hash(v)
    local tab = CRC.table()
    local hash = 0xFFFFFFFF
    for i = 1, #v do
        hash = xor(tab[band(xor(hash, v:byte(i)), 0xFF)], rshift(hash, 8))
    end
    return xor(hash, 0xFFFFFFFF)
end

return CRC