I'm trying to detect a mouse's XBUTTON1 and XBUTTON2 clicks using PreFilterMessage as suggested in an answer to my previous question, but am unsure about the how to read the WPARAM.
According to the WM_XBUTTONDOWN msdn page , I have to check the WPARAM's "high-order word" in order to distinguish between the two buttons. However, it seems from here that the size of WPARAM is different in x86 and x64. So how do I make sure it works on both?