build.sh

git clone git@github.com:LuaJIT/LuaJIT.git
cd LuaJIT
make
cd ..
gcc -O2 main.c -I LuaJIT/src/ -L LuaJIT/src/ -lluajit
./a.out main.lua

main.c

#include <stdio.h>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
#include <luajit.h>

static int isstring(lua_State *L) {
  lua_pushboolean(L, lua_isstring(L, 1));
  return 1;
}

int main(int argc, char *argv[])
{
  int status;
  lua_State *L;

  L = luaL_newstate(); // open Lua
  if (!L) {
    return -1; // Checks that Lua started up
  }

  luaL_openlibs(L); // load Lua libraries

  lua_register(L, "isstring", isstring);

  if (argc > 1) {
    status = luaL_loadfile(L, argv[1]);  // load Lua script
    int ret = lua_pcall(L, 0, 0, 0); // tell Lua to run the script
    if (ret != 0) {
      fprintf(stderr, "%s\n", lua_tostring(L, -1)); // tell us what mistake we made
      return 1;
    }
  }

  lua_close(L); // Close Lua
  return 0;
}

main.lua

local SysTime = _G.os.clock
local type = _G.type
local isstring = _G.isstring

local function benchmark(func)
	local count = 500000000 -- increase the iterations
	local StartTime = SysTime()

	for i = 1, count do
		func() -- don't bother passing arguments, it adds unesseceary time to the profiling
	end

	local EndTime = SysTime()

	return EndTime - StartTime .. " secs."
end

local testString = "jadevx4bo7nb7mof58lirs2im9fufbz5"

local function bench0()
	return type(testString) == "string"
end

local function bench1()
	return isstring(testString)
end

jit.on()
print("Type (JIT On): " .. benchmark(bench0))
print("isstring (JIT On): " .. benchmark(bench1))

jit.off()
print("Type (JIT Off): " .. benchmark(bench0))
print("isstring (JIT Off): " .. benchmark(bench0))

jit.on() -- Turn jit it back on