Benchmark for memoization of a simple index translation function

bench.lua

local ffi = require 'ffi'

local intidx_fnc do
	if ffi.abi('le') then
		function intidx_fnc(n)
			if n<1 or n>4 then
				error("wrong index", 2)
			end
			return n-1
		end
	else
		function intidx_fnc(n)
			if n<1 or n>4 then
				error("wrong index", 2)
			end
			return 4-n
		end
	end
end

local intidx_tab do
	intidx_tab = setmetatable({}, {__index = function(self, index)
		local res = intidx_fnc(index)
		rawset(self, index, res)
		return res
	end})
end

local function bench(f)
	local before = os.clock()
	f()
	return os.clock() - before
end

local function compare(vals)
	for key, value in pairs(vals) do
		print(key, bench(value))
	end
end

local num = 1e9
compare {
	['function'] = function()
		for i=1,num do
			local a = intidx_fnc(i % 3 + 1)
		end
	end;
	['table'] = function()
		for i=1,num do
			local a = intidx_tab[i % 3 + 1]
		end
	end;
}