[FFmpeg-devel] [PATCH] ARM: NEON optimised simple_idct
Mon Aug 25 22:17:45 CEST 2008
tOn Mon, Aug 25, 2008 at 09:04:27PM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> > On Mon, Aug 25, 2008 at 07:47:16PM +0100, M?ns Rullg?rd wrote:
> >> Michael Niedermayer <michaelni at gmx.at> writes:
> > [...]
> >> >2. depending on the pattern of non zero / all zero rows one of 8
> >> > optimized column transforms is used. This may be a bad idea though
> >> > for a CPU with a small code cache ...
> >> >
> >> > also maybe it would make sense to look at i386/idct_sse2_xvid.c
> >> > which uses SSE2 (128bit registers), this one uses only 16bit operations
> >> > for the column transform so it may be faster when the tricks of the simple
> >> > idct arent applicable
> >> Do you expect any sane person to be able to read that?
> > well, a little insanity may be needed
> >> That's also
> >> not bitexact, right?
> > it is supposed to be bitexact, and i cannot remember a case where any
> > input lead to different output. Also the MMX one is used in the
> > regression tests and they match between MMX and non x86 cpus ...
> All the different IDCT variants (int, simple, simplemmx, libmpeg2mmx,
> xvidmmx, faani) give different output on my machine with current
> FFmpeg. Which one is correct?
and if you really have a case where simple and simplemmx return different
output for the same and correctly permutated input then iam very interrested
> >> > also
> >> >
> >> > Intel 64 and IA-32 Architectures
> >> > Software Developers Manual
> >> > Volume 2A (and B)
> >> > Instruction Set Reference
> >> >
> >> > contains very readable and unambigious explanations of what all the
> >> > MMX, SSE* instruction do, if you ever want to decypher mmx or sse code
> >> I have those documents, and reading Chinese is easier.
> > This is great, so you can help me communicate with zhentan who is a SOC
> > student and IIRC chinese.
> No, but maybe he can explain mmx to me.
He may be able to write some mmx intro in chinese.
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Size: 189 bytes
Desc: Digital signature
More information about the ffmpeg-devel