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I'm trying to write code to iterate over files and registry
keys using a for loop iterator in Lua 4.1w4. However, my C
code always seem to be outperformed by Lua code.  A simple

  function iterator(max)
    local val = 0
    return function()
      if val < max then
        val = val + 1
        return val

  for i in iterator(10) do -- 1 to 10

If I try to write 'iterator' via the C API, it is *slower*
than the Lua code.  Here's my C translation:

  int lua_iterator_next(lua_State* L)
    int max = (int) lua_tonumber(L, lua_upvalueindex(1));
    int cur = (int) lua_tonumber(L, lua_upvalueindex(2));
    if (cur < max)
      lua_pushnumber(L, cur);
      lua_replace(L, lua_upvalueindex(2));
      lua_pushnumber(L, cur);
      return 1;

    return 0;

  int lua_iterator_create(lua_State* L)
    lua_pushvalue (L,1); // arg is 'max', make it first upvalue
    lua_pushnumber(L,0); // next upvalue is our 'current value'
    lua_pushcclosure(L, lua_iterator_next, 2);
    return 1;


  lua_registry(L, "iterator", lua_iterator_create);

Testing with a simple for loop 'for i in iterator(200000) do
end', I find the Lua code is roughly 25% faster than the C
code.  What am I doing wrong?


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