OT (perhaps), Ray\Box intersection........

I’m moving over from lazy selection (OpenGL selection buffer) to ray intersection testing (for mouse hits etc.). Anyone have a good and really fast ray\aligned box intersection test? I don’t need the intersection point, just need to know if the ray ( origin --> direction ) intersects the box ( topleftback, bottomrightfront ).

I went to Magic Software but can’t quite make head nor tail of his implementation. Surely YOU ALL must have this little method in your toolboxes?

Thanks for any help.