[FFmpeg-devel] [PATCH 7/9] lavfi/nlmeans: switch from double to float

[Clément Bœsch]

On Sun, May 06, 2018 at 04:53:54PM +0200, Moritz Barsnick wrote:
> On Sun, May 06, 2018 at 13:40:58 +0200, Clément Bœsch wrote:
> > Overall speed appears to be 1.1x faster with no noticeable quality impact.
> 
> Probably platform dependant?
> 
> >  struct weighted_avg {
> > -    double total_weight;
> > -    double sum;
> > +    float total_weight;
> > +    float sum;
> >  };
> 
> I believe these calculaions in nlmeans_plane() will promote to double
> before being cast back to float:
> 
>            // Also weight the centered pixel
>             wa->total_weight += 1.0;
>             wa->sum += 1.0 * src[y*src_linesize + x];
> 
> (At least the second one. The first one - just an assignment of a
> constant - is covered by the preprocessor, IIUC.) They need to use
> "1.0f".
> 

It doesn't really matter here actually, in "lavfi/nlmeans: move final
weighted averaging out of nlmeans_plane" you can see that this code
represents 0.24% of the CPU time. I fixed it locally anyway, thanks.

> (There are others, but only in init(), which don't matter for
> performance.)

Yeah, I left these to double on purpose.

-- 
Clément B.
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