[FFmpeg-devel] [PATCH] adpcm: Clarify a comment

[Martin Storsjö]

On Wed, 3 Nov 2010, Michael Niedermayer wrote:

> On Wed, Nov 03, 2010 at 09:07:26PM +0200, Martin Storsjo wrote:
> > ---
> >  libavcodec/adpcm.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/libavcodec/adpcm.c b/libavcodec/adpcm.c
> > index 455b477..f298ef5 100644
> > --- a/libavcodec/adpcm.c
> > +++ b/libavcodec/adpcm.c
> > @@ -354,7 +354,7 @@ static void adpcm_compress_trellis(AVCodecContext *avctx, const short *samples,
> >          int sample = samples[i*stride];
> >          memset(nodes_next, 0, frontier*sizeof(TrellisNode*));
> >          for(j=0; j<frontier && nodes[j]; j++) {
> > -            // higher j have higher ssd already, so they're unlikely to use a suboptimal next sample too
> > +            // higher j have higher ssd already, so they're likely to yield a suboptimal next sample too
> 
> how much is gained without that assumtion?

Current code:
stddev:   31.99 PSNR: 66.23 MAXDIFF: 2643 bytes:  2646016/  2649218
Runtime 16.6 s

range = 1 for all nodes:
stddev:   31.97 PSNR: 66.23 MAXDIFF: 2112 bytes:  2646016/  2649218
Runtime 19.3 s

So I think the general idea of the assumption is quite good as such, since 
it gives quite a big gain in performance compared to the. With this patch 
in place, the comment says what the code actually does.

// Martin