crc32.lua

local sysnative = not not package.loadlib
local datacard = nil
if not sysnative then
	local component = require("component")
	if component.isAvailable("data") then
		datacard = component.data
	end
end

-- CRC32 implementation
-- standard table lookup version
local crctab = {}

local i
for i=0,256-1 do
	local j
	local v = i
	--[[
	v = ((v<<4)|(v>>4)) & 0xFF
	v = ((v<<2)&0xCC)|((v>>2)&0x33)
	v = ((v<<1)&0xAA)|((v>>1)&0x55)
	]]

	for j=1,8 do
		if (v&1) == 0 then
			v = v>>1
		else
			v = (v>>1) ~ 0xEDB88320
		end
	end
	crctab[i+1] = v
end

local crc = {}
function crc.crc32(str, v)
	v = v or 0
	if v == 0 and datacard ~= nil then
		local a = datacard.crc32(str)
		v = string.byte(a, 1) | (string.byte(a, 2) << 8) | (string.byte(a, 3) << 16)
		v = v | (string.byte(a, 4) << 24)
		return v
	end
	v = v ~ 0xFFFFFFFF

	local i
	for i=1,#str do
		--print(str:byte(i))
		v = (v >> 8) ~ crctab[((v&0xFF) ~ str:byte(i))+1]
	end

	v = v ~ 0xFFFFFFFF
	return v
end

return crc