[Ffmpeg-devel] [REQUEST] MMX/MMX2 and SSE optimizations for H.264 decoding

Michael Niedermayer michaelni
Thu Sep 15 20:44:14 CEST 2005


On Thu, Sep 15, 2005 at 09:52:42AM -0700, Loren Merritt wrote:
> On Thu, 15 Sep 2005, Martin Boehme wrote:
> >Gamester17 wrote:
> >>Yes there already are some MMX integer optimization for H264 but what 
> >>about SSE (Streaming SIMD Extensions) optimizations?, isn't SSE suppose 
> >>to be much more powerfull than MMX (and in fact be the thing that 
> >>replaces MMX)?
> >
> >Well, for a start, SSE has registers that are 128 bits wide, while MMX's 
> >registers are 64 bits. As long as you're operating only on the registers 
> >(i.e. you're CPU-bound, not memory bandwidth limited) that's an instant 
> >factor of 2 speedup.
> On AMD, most SSE2 instructions take exactly twice as long as the 
> equivalent MMX instruction. Any speedups are due only to scheduling.
> In x264, we have a bunch of SSE2 functions, but most of them are _slower_ 

what about porting the ones which are not slower to ffmpeg? puting them under
CONFIG_GPL would be perfectly fine if the authors prefer that
someone also should compare the differing MMX routines in x264 and ffmpeg and
port the faster ones to the other project ...


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