[FFmpeg-devel] [PATCH 2/3] avcodec/gdv: Optimize and factorize scaling loops

[Michael Niedermayer]

On Sat, Jan 12, 2019 at 04:49:40PM +0100, Carl Eugen Hoyos wrote:
> 2019-01-12 16:46 GMT+01:00, Michael Niedermayer <michael at niedermayer.cc>:
> > On Sat, Jan 12, 2019 at 04:07:42PM +0100, Carl Eugen Hoyos wrote:
> >> 2019-01-04 20:22 GMT+01:00, Michael Niedermayer <michael at niedermayer.cc>:
> >>
> >> > +static void scaledown(uint8_t *dst, const uint8_t *src, int w)
> >> > +{
> >> > +    int x;
> >> > +    for (x = 0; x < w - 7; x+=8) {
> >> > +        dst[x + 0] = src[2*x + 0];
> >> > +        dst[x + 1] = src[2*x + 2];
> >> > +        dst[x + 2] = src[2*x + 4];
> >> > +        dst[x + 3] = src[2*x + 6];
> >> > +        dst[x + 4] = src[2*x + 8];
> >> > +        dst[x + 5] = src[2*x +10];
> >> > +        dst[x + 6] = src[2*x +12];
> >> > +        dst[x + 7] = src[2*x +14];
> >>
> >> Could you add to the commit message the information
> >> which compiler is able to optimize this?
> >> (Assuming this is a reason for the speedup)
> >
> > if what you ask for is "which compiler turns this into SIMD"
> > i do not know, and i suspect mine does not from the limited
> > increase in performance
> > I think the speedup is primarly from simply unrolling the trivial loop
> >
> > is there something you want me to change in the commit message still ?
> 
> No, I am a little surprised that unrolling without SIMD makes
> a difference.

will apply

thx


> 
> Thank you for the explanation, Carl Eugen
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-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct answer.
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