Due to C arithmetic conversion rules we must use an unsigned constant (or a
 cast) to perform the multiplication using unsigned arithmetic.

 Fixes ArcticaProject/nx-libs#55.

 Author: Emanuele Giaquinta <emanuele.giaquinta@gmail.com>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>
 Rebased against NX: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>