[FFmpeg-devel] [PATCH] Fix function parameters for rgb48 to YV12 functions.

[Michael Niedermayer]

On Tue, Feb 02, 2010 at 08:21:15PM +0100, Reimar D?ffinger wrote:
> On Tue, Feb 02, 2010 at 08:01:26PM +0100, Michael Niedermayer wrote:
> > On Tue, Feb 02, 2010 at 04:10:06PM -0200, Ramiro Polla wrote:
> > > Hello Michael,
> > > 
> > > On Sun, Jan 24, 2010 at 8:31 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > > > the gain happens when you change the variables used to calculate the index
> > > > also to it. You could also try to make the index unsigned but make sure it
> > > > cant be negative if you try this
> > > 
> > > Sorry but I still don't understand how that will be of use here in
> > > libswscale. I've tried forcing int32_t and int64_t for x86_64 in some
> > > of those functions (some xxxTo(Y|UV), hScale and the fast bilinear
> > > ones), in all C, MMX and MMX2. All I can see is the expansion from
> > > 32-bit to 64-bit being changed from caller and callee. There is no
> > > difference in the inner loop, nor in how gcc addresses the the src and
> > > dst arrays.
> > 
> > maybe theres no gain for swscale, i cant say without looking at the asm
> > gcc generates.
> > i know that in h264 gcc filled some functions with 32->64 sign extension
> > code in the inner loops.
> 
> Which compilation options have you been using?

default of ffmpeg & gcc-4.4
also a quick
grep movslq libavcodec/h264_loopfilter.S | grep -v '('
    68     136    1220

and with -mtune=core2 -march=core2 -mcpu=core2
grep movslq libavcodec/h264_loopfilter.S | grep -v '(' |wc
    68     136    1226

so no, its not helping it still does produce all the register-register
sign extensions


> IIRC sign extension is only an issue when gcc uses the indexed load instructions,
> which it does not use at all anymore when optimizing for a more modern CPU
> (which means it ends up being even shorter on registers and thus creating
> larger and slower code with probably theoretically better instruction scheduling).
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-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I am the wisest man alive, for I know one thing, and that is that I know
nothing. -- Socrates
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