boxed_integer.lua

--[[
    The MIT License (MIT)
    Copyright (c) Cheyi Lin <cheyi.lin@gmail.com>
]]

local bit_xor
if jit and jit.version_num > 20000 then
    bit_xor = bit.bxor
else
    bit_xor = bit32.bxor
end

-- XOR secret
local secret = 0x3e

local function crypt(s)
    local s = s:gsub(".", function (c) return string.char(bit_xor(c:byte(), secret)) end)
    return s
end

-- module xint
local xint = {}

function xint:new(n)
    local o = setmetatable({}, self)
    self.__index = self
    self.__tostring = self.tostring
    self.__metatable = false
    o:set(n)
    return o
end

function xint:set(n)
    self.v = crypt(tostring(n))
end

function xint:get()
    return tonumber(crypt(self.v))
end

function xint:tostring()
    return crypt(self.v)
end

-- test
local function printf(fmt, ...)
    io.write(string.format(fmt, ...))
end

local function dump_hex(s)
    printf("[%d] ", #s)
    s:gsub(".", function (s) printf("%02x ", s:byte()) end)
    printf("\n")
end

-- initial number
local n = 1001
printf("n: %d (%s)\n", n, type(n))
dump_hex(tostring(n))

-- create xint object
local x = xint:new(n)
printf("x: %s (%s)\n", tostring(x), type(x))
dump_hex(x.v)

-- get number from xint object
local xn = x:get()
printf("xn: %d (%s)\n", xn, type(xn))

-- set number to xint object
x:set(xn + 100000)
printf("x: %s (%s)\n", tostring(x), type(x))
dump_hex(x.v)

Result:

n: 1001 (number)
[4] 31 30 30 31 
x: 1001 (table)
[4] 0f 0e 0e 0f 
xn: 1001 (number)
x: 101001 (table)
[6] 0f 0e 0f 0e 0e 0f