[FFmpeg-devel] [PATCH] AAC: unroll parts of decode_spectrum_and_dequant()

Alex Converse alex.converse
Tue Dec 9 04:34:55 CET 2008


On Mon, Dec 8, 2008 at 9:33 PM, Jason Garrett-Glaser
<darkshikari at gmail.com>wrote:

> On Mon, Dec 8, 2008 at 3:43 PM, Alex Converse <alex.converse at gmail.com>
> wrote:
> > Hi,
> >
> > The attached patch unrolling sections of decode spectrum saves me 5.48%
> on
> > my mpeg4-lc-256kbps stream on my core2 duo.
> >
> > Regards,
> > Alex Converse
>
> If dim can only be 2 or 4, wouldn't it be better to do
>
> if( dim == 4 ) {
> do dim 4 stuff
> }
> do dim 2 stuff
>
> The switch seems unnecessary.
>

Idiomatically I like the switch better but your way is faster. When I did
that I also tried reverting access back to forward order and got a slight
speed up. This way made the unsigned loop just like the other three, so I
added that one for another benchmarked verified speed up.

The net gain is a 12% decrease in cycles over the original vs 5% before.

--Alex
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