[FFmpeg-devel] r9017 breaks WMA decoding on Intel Macs

Guillaume POIRIER poirierg
Thu May 31 08:20:54 CEST 2007


Hi,

On 5/31/07, Trent Piepho <xyzzy at speakeasy.org> wrote:
> On Thu, 31 May 2007, Guillaume POIRIER wrote:
> > On 5/30/07, Michael Niedermayer <michaelni at gmx.at> wrote:
> > > On Wed, May 30, 2007 at 02:07:19PM +0200, Guillaume POIRIER wrote:
> > > > Ok, fine with me. Michael, do you think that the patch I posted
> > > > earlier (100% based on Trent's, only fixing minor issues) should be
> > > > applied?
> > >
> > > well, after actually reading the code ... the loops should be written
> > > in asm not by using for() / while() this will make the code faster
> > > and it will make the n+%m code naturally dissapear
> >
> > Well, after getting a hint from Apple guys, here's an updated patch
> > that gets rid of all assembler warnings without touching the code as
> > much as Trent had done.
> >
> > Now, maybe writing the loop in ASM ourselves will help, but at least,
> > this patch doesn't harm and works on all supported platforms!
>
> This won't assemble correctly if any of the memory operands already have a
> displacement. Loren explained why:
> http://article.gmane.org/gmane.comp.video.ffmpeg.devel/51453

I agree. This patch's main purpose is to show how to write this
routine with proper syntax (Bear in mind that all assemblers produce a
warning here. To a certain extend, we may consider that the reason it
works with FSF AS is just by pure luck.)

When I have the time, I shall benchmark both yours and my patch to see
what are the speed figures.... But IMHO, it's a bit pointless, because
whatever the speed figures may look like, we are comparing 1 solution
that appears to work by luck, and another that is more reliable. Speed
isn't what your patch is after.
I mean: how good is it to benchmark an optimized routine if it's broken?

Anyway, I'm sure the benchmark figures will be appreciated by Michael,
so I'll make them.

Guillaume
-- 
Y'a pas de gonzesse hooligan,
Imb?cile et meurtri?re
Y'en a pas m?me en grande Bretagne
A part bien s?r Madame Thatcher
  -- Renaud (sur "Miss Maggie")



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