Re: [mpeg2-dev] mmxext acceleration

[Gour <go...@go...>]

On Sat, 28 Nov 2009 13:22:21 +0200
>>>>>> "Rémi" == "Rémi Denis-Courmont" <re...@re...> wrote:

Rémi> AFAIK, MMX extensions are the subset of SSE which is safe on
Rémi> operating systems that don't support SSE. Hence, it is perfectly
Rémi> normal that you don't find it in the CPU flags - it is implied by SSE.

Here is the reply I got on transcode list which confirms  my 'theory'...

<quote>
>Francesco> `mmxext' is deep jargon (mostly found on linux field AFAIK)
>Francesco> for some MMX extended instructions that aren't explicitly
>Francesco> advertised; I can't recall the exact details but those were
>Francesco> added together with the first round of SSE or something like
>Francesco> that.
>Francesco> So, unless I missing something huge, the core i7 definitley
>Francesco> support them :)  

I'm afraid you're missing something. (:  MMXEXT (like 3DNow!) is an
AMD-specific extension that was added in some old AMD CPUs back before
AMD and Intel settled on a common SIMD instruction set.  The MMXEXT
instructions have since been superseded by SSE in both AMD and Intel CPUs,
so Intel never added support for them.

The solution to this particular problem is to fix the following bug in
libmpeg2:

>#if defined(ARCH_X86) || defined(ARCH_X86_64)
>static inline uint32_t arch_accel (uint32_t accel)
>{  
[...]
>    if (accel & (MPEG2_ACCEL_X86_SSE2 | MPEG2_ACCEL_X86_SSE3))
>	accel |= MPEG2_ACCEL_X86_MMXEXT;  

"MMXEXT" should be changed to "MMX" here (or the clause should be deleted
entirely if the MMX flag is not needed in SSE environments).
</quote>


Sincerely,
Gour

-- 

Gour  | Hlapicina, Croatia  | GPG key: F96FF5F6
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