lua_tonumberx
lua_Number d = lua_tonumberx(L, narg, &isnum);
lua_Number n = lua_tonumberx(L, 1, &isnum);
LUA_API lua_Number (lua_tonumberx) (lua_State *L, int idx, int *isnum);
#define lua_tonumber(L,i) lua_tonumberx(L,i,NULL)