Get rounding mode in LuaJIT

main.lua

local ffi = require("ffi")
ffi.cdef("double nextafter(double from, double to);")

local small = ffi.C.nextafter(0, 1)

local modes = {
	nearest_toEven = {2, 2, -2, -2},
	nearest_truncate = {2, 3, -2, -3},
	truncate = {1, 2, -1, -2},
	ceiling = {2, 3, -1, -2},
	floor = {1, 2, -2, -3}
}

local input = {1.5, 2.5, -1.5, -2.5}

local function getRoundingMode()
	for name, results in pairs(modes) do
		local this = true
		for i = 1, 4 do
			if small * input[i] ~= small * results[i] then
				this = false
				break
			end
		end
		if this then return name end
	end
end

print(getRoundingMode())

function love.draw()
	love.graphics.print(getRoundingMode())
end