[FFmpeg-devel] [PATCH] swscale: avoid overread in planar2x

[Michael Niedermayer]

On Sun, Sep 12, 2010 at 11:16:53AM -0300, Ramiro Polla wrote:
> On Sun, Sep 12, 2010 at 10:43 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Sun, Sep 12, 2010 at 10:00:07AM -0300, Ramiro Polla wrote:
> >> On Sun, Sep 12, 2010 at 7:44 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> [...]
> >> > after a second look i see that the C code overrides the first pixel and thus
>                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >> > the output should not be affected, still my suggestion though seems nicer than
> >> > requireing all buffers to have a byte allocated before them
> >>
> >> Thanks for the suggestion. Patch attached. No speed difference measured.
> >
> >> ?rgb2rgb_template.c | ? ?4 +++-
> >> ?1 file changed, 3 insertions(+), 1 deletion(-)
> >> 9c5b0f0bc55c99bcfbda486bff43d26c34cb96f5 ?planar2x_avoid_overread_2.diff
> >> Index: rgb2rgb_template.c
> >> ===================================================================
> >> --- rgb2rgb_template.c ? ? ? ?(revision 32166)
> >> +++ rgb2rgb_template.c ? ? ? ?(working copy)
> >> @@ -1773,12 +1773,13 @@ static inline void RENAME(planar2x)(const uint8_t
> >> ? ? ? ? ?const x86_reg mmxSize= srcWidth&~15;
> >> ? ? ? ? ?__asm__ volatile(
> >> ? ? ? ? ? ? ?"mov ? ? ? ? ? %4, %%"REG_a" ? ? ? ? ? ?\n\t"
> >> + ? ? ? ? ? ?"movq ? ? ? ? (%0, %%"REG_a"), %%mm4 ? ?\n\t"
> >> + ? ? ? ? ? ?"psllq ? ? ? ? ? ? ? ? ? ? $8, %%mm4 ? ?\n\t"
> >
> > the first value is then 0 which would lead to a darker border pixel
> 
> Which is overwritten by the C code. Or did I miss something?

dont you want to beat the c code speedwise? 

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I wish the Xiph folks would stop pretending they've got something they
do not.  Somehow I fear this will remain a wish. -- M?ns Rullg?rd
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