[FFmpeg-devel] [PATCH] SSE optimization for DCA decoder

Robert Swain robert.swain
Fri Aug 29 12:38:46 CEST 2008

2008/8/29 Alexander E. Patrakov <patrakov at gmail.com>:
> David Conrad wrote:
>> Attached gives me about a 45% faster overall DCA decode on my penryn.
>> Name suggestions for the function welcome.
> I think that we should completely rewrite this QMF instead (at the very
> least, in order to get rid of the name "subband_fir_noidea") and express it
> in terms of convolution (or scalar product) combined with a 32-point DCT
> (which is already available in the optimized form). When writing my DCA
> encoder, I had to treat this QMF as a linear black-box instead of
> understanding the existing code. The reason is that the code is almost a
> verbatim copy from the spec, and the spec has been obviously obfuscated in
> order to make writing the encoder harder. Thus, I want to share some
> algebraic properties of the transform, in order to inspire you to write a
> better C implementation of it (based on this understanding).



I will need analysis (32-subband; real-valued time domain to
complex-valued and hence oversampled output) and synthesis (normal -
64-subband, downsampled - 32-subband; complex-valued input to
real-valued time domain) QMFs for SBR so this may be useful to me too.
I don't know if David wants to look at this and he's certainly welcome
to but if he doesn't look at it, maybe I will.


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