[FFmpeg-devel] [PATCH] Some ARM VFP optimizations (vector_fmul, vector_fmul_reverse, float_to_int16)

Michael Niedermayer michaelni
Mon Apr 21 01:00:05 CEST 2008

On Mon, Apr 21, 2008 at 01:50:50AM +0300, Siarhei Siamashka wrote:
> > > 2. Assuming you do need one, where was the problem with using a recent
> > > gcc which supports maintaining stack alignment?
> > > 3. What effect does your solution have on systems which do align the
> > > stack aka a recent gcc on pre EABI. Or even a non gcc compiler.
> Please explain me how exactly recent gcc would align stack on pre EABI system?
> If you want to suggest something like '-mpreferred-stack-boundary', that
> option is only supported for x86 ('-m' prefix in general means machine
> dependent option).


> And I would not even consider non gcc compiler right now, that's a waste of
> time. Whatever you suppose or try to guess about this compiler has a high
> probability to turn out wrong. Please remember that we are speaking about
> assembly code here, not just C99 or whatever covered by some standards.

compile asm with gcc, compile rest with something else
asm in that case is called by "somehing else" and that might support aligning
the stack.

> > To awnser 3.
> > huge speedloss, and thats why this isnt a solution
> Where did you get this idea? Actually using current FFmpeg implementation of
> ARMv5TE IDCT is a huge speedloss :)
> The proposed upgrade is not perfect, but it still can be improved further. And
> it will provide performance improvement, and provide it right now. Before this
> hardware (ARMv5TE is already old) gets completely outdated and abandoned by 
> everyone...

Well if you insist on this messy stack realign in the innermost loop then iam
fine with it, if you provide some benchmarks (with the realign enabled) which
are faster than the current code.

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

it is not once nor twice but times without number that the same ideas make
their appearance in the world. -- Aristotle
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