uint16 to two uint8

local id = 0 -- number between 0 and 2^16-767

local id, id2, l, r, l2, r2, id2, high
function test()
    for i = 0, 2^16-1-766 do
        id = i
        -- code to chars
         high = math.floor(id / 254)
         l = high +1
         r = id - high * 254 +1

        -- insert to text
        local header = string.char(l)..string.char(r)

        -- extract from text
        l2 = string.byte(header:sub(1,1))
        r2 = string.byte(header:sub(2,2))

        -- decode from chars
        id2 = (l2-1)*254 + r2-1

        if id ~= id2 or l == 0 or r == 0 or l2 == 0 or r2 == 0 then
            error("values do not match")
        end
    end
end

local success, err = pcall(test)
if not success then
    print(success, err)
    print("errored with", id, id2, l, r, l2, r2, id2, high)
else
    print("success :)")
end