This ensures gcc does not create unnecessary
loads or stores and possibly even does not vectorize
the negation.
Speeds up mp3 to aac transcoding with default settings
by 10% when using "gcc (Debian 5.3.1-10) 5.3.1 20160224".
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>