Hi,
On Sun, Jul 12, 2015 at 10:29 AM, Paul B Mahol <one...@gmail.com> wrote:
> Dana 12. 7. 2015. 14:18 osoba "Ronald S. Bultje" <rsbul...@gmail.com>
> napisala je:
> >
> > Hi,
> >
> > On Sun, Jul 12, 2015 at 6:48 AM, Paul B Mahol <one...@gmail.com> wrote:
> >
> > > Dana 12. 7. 2015. 01:56 osoba "Ronald S. Bultje" <rsbul...@gmail.com>
> > > napisala je:
> > > >
> > > > ---
> > > > libavfilter/vf_ssim.c | 5 ++---
> > > > 1 file changed, 2 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/libavfilter/vf_ssim.c b/libavfilter/vf_ssim.c
> > > > index 0721ddd..3ef122f 100644
> > > > --- a/libavfilter/vf_ssim.c
> > > > +++ b/libavfilter/vf_ssim.c
> > > > @@ -134,7 +134,7 @@ static float ssim_end1(int s1, int s2, int ss,
> int
> > > s12)
> > > > / ((float)(fs1 * fs1 + fs2 * fs2 + ssim_c1) * (float)(vars
> +
> > > ssim_c2));
> > > > }
> > > >
> > > > -static float ssim_end4(int sum0[5][4], int sum1[5][4], int width)
> > > > +static float ssim_endn(int (*sum0)[4], int (*sum1)[4], int width)
> > > > {
> > > > float ssim = 0.0;
> > > > int i;
> > > > @@ -169,8 +169,7 @@ static float ssim_plane(uint8_t *main, int
> > > main_stride,
> > > > &sum0[x]);
> > > > }
> > > >
> > > > - for (x = 0; x < width - 1; x += 4)
> > > > - ssim += ssim_end4(sum0 + x, sum1 + x, FFMIN(4, width - x
> -
> > > 1));
> > > > + ssim += ssim_endn(sum0, sum1, width - 1);
> > > > }
> > > >
> > > > return ssim / ((height - 1) * (width - 1));
> > > > --
> > > > 2.1.2
> > > >
> > > >
> > >
> > > Why? There was reason behind this code I guess.
> > >
> >
> > I think it's for simd code simplification. See, I'm guessing the code you
> > took from libvpx had an extra condition to do only 4-sized chunks through
> a
> > function pointer, and then the odd tail in c code. If you do this, the
> simd
> > code has a fixed size (always 4), which makes the implementation much
> more
> > trivial: 4 16-byte loads, add, transpose4x4d, and then ssim_end1 to get 4
> > results, which you horizontal-add and return.
> >
>
> I took this from tiny_ssim.c as pengvado said its ok to relicense to lgpl.
I think the same reasoning still applies - this will get better
performance, particularly if we consider avx2.
Ronald
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