[FFmpeg-devel] [PATCH] SSE2 Xvid idct

[Pascal Massimino]

  Re,

On Sun, Apr 6, 2008 at 9:39 PM, Pascal Massimino <pascal.massimino at gmail.com>
wrote:

>
>
> >
> > [...]
> > >     "movdqa   %%xmm2, ("dct")         \n\t" \
> > >     "movdqa   %%xmm3, %%xmm2          \n\t" \
> > >     "psubsw   %%xmm6, %%xmm3          \n\t" \
> > >     "paddsw   %%xmm2, %%xmm6          \n\t" \
> > >     "movdqa   %%xmm6, %%xmm2          \n\t" \
> > >     "psubsw   %%xmm7, %%xmm6          \n\t" \
> > >     "paddsw   %%xmm2, %%xmm7          \n\t" \
> > >     "movdqa   %%xmm3, %%xmm2          \n\t" \
> > >     "psubsw   %%xmm5, %%xmm3          \n\t" \
> > >     "paddsw   %%xmm2, %%xmm5          \n\t" \
> > >     "movdqa   %%xmm5, %%xmm2          \n\t" \
> > >     "psubsw   %%xmm0, %%xmm5          \n\t" \
> > >     "paddsw   %%xmm2, %%xmm0          \n\t" \
> > >     "movdqa   %%xmm3, %%xmm2          \n\t" \
> > >     "psubsw   %%xmm4, %%xmm3          \n\t" \
> > >     "paddsw   %%xmm2, %%xmm4          \n\t" \
> > >     "movdqa  ("dct"), %%xmm2          \n\t" \\
>
>
 oh! now i recall an optim: you don't need to
 save and recall xmm2 in "dct", provided you replace
 the first butterfly :

>     "movdqa   %%xmm3, %%xmm2          \n\t" \
>     "psubsw   %%xmm6, %%xmm3          \n\t" \
>     "paddsw   %%xmm2, %%xmm6          \n\t" \

 by its (non-saturating) sub,add,add equivalent:

psubw %%xmm6,%%xmm3
paddw %%xmm6,%%xmm6
paddw %%xmm3,%%xmm6

skal