I think this is a little more efficient than dxdy, and easier to read. We call DxDy2 a lot, can any of those use Angle/DirAngle?
/*
** $Id: lapi.h,v 2.2.1.1 2007/12/27 13:02:25 roberto Exp $
** Auxiliary functions from Lua API
** See Copyright Notice in lua.h
*/
#ifndef lapi_h
#define lapi_h
#include "lobject.h"
LUAI_FUNC void luaA_pushobject (lua_State *L, const TValue *o);
#endif