[FFmpeg-cvslog] r14475 - trunk/libavutil/internal.h

Reimar Döffinger Reimar.Doeffinger
Wed Jul 30 19:46:08 CEST 2008


On Wed, Jul 30, 2008 at 05:02:17PM +0100, M?ns Rullg?rd wrote:
> Reimar D?ffinger wrote:
> > fast_memcpy is GPL, so that might complicate things a bit.
> > It will complicate things even more, since it will speed up some things
> > and slow down other things (esp. memcpy with constant size which is
> > replaced by a compiler builtin otherwise).
> 
> In other words, its utility is questionable.  Why does mplayer use it,
> if it is not good for anything?

Because it is _hugely_ faster e.g. on an x86 system with a generic i386 libc
and an MPlayer compiled for an CPU with MMX when copying a full video
frame. Doubly so when copying e.g. to video memory.

> > I once started to make fast_memcpy uses explicit in MPlayer where they
> > helped performance and get rid of it where it does not, but it is still
> > incomplete.
> 
> How much of a difference does it make, anyway?  Perhaps the best solution
> is to simply drop, except perhaps in a few critical places.

Yes, of course, that was my intention.

> I have one more option:
> 
> 3. Move this nasty hack to mplayer, where it belongs.

Well, I can do that, too:
4. Keep it as a nasty reminder that FFmpeg does not have an optimized
memcpy yet (though admittedly FFmpeg does not do that much copying
around)...

Greetings,
Reimar D?ffinger




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