hash_map vs lua table

map.cpp

extern "C" {
#include "lua.h"
#include "lauxlib.h"
}

#include <string>
#include <ext/hash_map>

using namespace std;
using namespace __gnu_cxx;

namespace __gnu_cxx {
    template<> struct hash<string>
    {
        size_t operator()(const string& s) const
        {
            return __stl_hash_string(s.c_str());
        }
    };
}

hash_map<int, int> _m;
hash_map<string, string> _ms;

extern "C"{
static int _set(lua_State *L) {
    lua_Integer k = luaL_checkinteger(L, 1);
    lua_Integer v = luaL_checkinteger(L, 2);
    _m[(int)k] = (int)v;
    return 0;
}

static int _get(lua_State *L) {
    lua_Integer k = luaL_checkinteger(L, 1);
    lua_pushinteger(L, (int)_m[(int)k]);
    return 1;
}

static int _sets(lua_State *L) {
    const char* k = luaL_checkstring(L, 1);
    const char* v = luaL_checkstring(L, 2);
    _ms[string(k)] = string(v);
    return 0;
}

static int _gets(lua_State *L) {
    const char* k = luaL_checkstring(L, 1);
    lua_pushstring(L, _ms[string(k)].c_str());
    return 1;
}
LUAMOD_API int luaopen_map(lua_State *L) {
        luaL_Reg l[] = {
                { "get", _get},
                { "set", _set},
                { "gets", _gets},
                { "sets", _sets},
                { NULL, NULL },
        };
        luaL_newlib(L,l);
        return 1;
}
}

result.txt

lmap consume:   2.633608
cmap consume:   2.532202
lmaps consume:  12.284357
cmaps consume:  9.247168

scripts.sh

g++ -O3 -fPIC -shared -o map.so map.cpp & lua table_perf.lua

table_perf.lua

local count = 10000000

local lmap = {}

local cmap = require "map"
local lmap = {}
local lmaps = {}

local function check_cmap()
    for i=1, count do
        cmap.set(i*137,i)
    end

    for i=1, count do
        if cmap.get(i*137) ~= i then
            error(i)
        end
    end
end

local function check_lmap()
    for i=1, count do
        lmap[i*137] = i
    end

    for i=1, count do
        if lmap[i*137] ~= i then
            error(i)
        end
    end
end

local function check_cmaps()
    for i=1, count do
        local v = tostring(i)
        cmap.sets(v, v)
        if cmap.gets(v) ~= v then
            error(i)
        end
    end
end

local function check_lmaps()
    for i=1, count do
        local v = tostring(i)
        lmaps[v] = v
        if lmaps[v] ~= v then
            error(i)
        end
    end
end

local function bench(f)
    local t0 = os.clock()
    f()
    local t1 = os.clock()
    return t1 - t0
end

print("lmap consume:", bench(check_lmap))
print("cmap consume:", bench(check_cmap))
print("lmaps consume:", bench(check_lmaps))
print("cmaps consume:", bench(check_cmaps))