[speex-dev] [PATCH] Make SSE Run Time option.

[Jean-Marc Valin]

> You may wish to save space for PNI.
> 
> 	http://cedar.intel.com/media/pdf/PNI_LEGAL3.pdf

Seems to be interesting instructions for complex arithmetic there (thus
helping FFTs). I'm not sure there's anything useful for Speex, though.
We'll see. What I think is much more promising is the x86-64 version of
SSE with 16 registers. That could speed up the filters a lot.

> Please note that dot products of simple vector floats are usually faster
> in the scalar units. The add across and transfer to scalar is just too
> expensive. Its generally only worthwhile if the data starts and ends in
> the vector units, and it is inlined so that latencies can be covered with
> other work. e.g:

Actually, even with a scalar unit, the best code is implicitly
vectorized. If you look at the original code I had, there are 4 partial
sums that prevents some stalling due to dependencies. From there, it's
easy to vectorize by 4 and add at the end. Note that for Speex the
vectors are either 40 or 160 samples long. The whole process is also
repeated 128 times in a row, so I think a vector unit will do much
better. 

        Jean-Marc


-- 
Jean-Marc Valin, M.Sc.A., ing. jr.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada


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