[Pixman] bilinear fast path

[Siarhei Siamashka]

On Tuesday 16 March 2010, Alexander Larsson wrote:
> On Tue, 2010-03-16 at 09:49 +0200, Siarhei Siamashka wrote:
> > On Monday 15 March 2010, Alexander Larsson wrote:
> > > On Mon, 2010-03-15 at 17:05 +0200, Siarhei Siamashka wrote:
> > > > Really good performance improvements for bilinear scaling are
> >
> > going to
> >
> > > > come
> > > > from SIMD optimizations. To make it happen, scaler core needs to
> >
> > be
> >
> > > > isolated
> > > > into a small simple function with a minimal number of checks and
> > > > branches.
> >
> > http://cgit.freedesktop.org/~alexl/pixman/commit/?h=fast-bilinear&id=a
> > 79daa
> >
> > >8453560b4193b848e51b4942dcdcd74c8d
> > >
> > > The "/* Main columns: */" part there is probably a good start for
> >
> > that.
> >
> > Yes, I know :)  Just a switch on different repeat cases needs to be
> > eliminated
> > and it should become quite easy to vectorize. Removal of this switch
> > may also
> > improve performance of generic C code a bit more.
>
> Switch? The main (i.e. non-border) pixels have straight linear code:
>
> http://cgit.freedesktop.org/~alexl/pixman/tree/pixman/pixman-fast-path.c?h=
>fast-bilinear#n1854
>
> There is no switch (or other repeat handling) in there, because we're
> using FAST_PATH_SAMPLES_COVERS_CLIP.

Yeah, looked at the wrong loop, sorry.

This one would benefit from knowing the exact number of iterations to run
beforehand (and thus eliminating 'vx < max_vx - pixman_fixed_1' part of
condition), so that this loop could be unrolled easily. And isolating this
inner loop into a separate function with clearly defined intput/output
arguments would help.

But this is a natural next step for optimization. Current step needs to be
finalized and committed first.

-- 
Best regards,
Siarhei Siamashka