[vorbis-dev] Optimisations

[Timothy J. Wood]

>This sounds great! Are these extensions weel-thought out? Where can I
>get-em? I'll look at mot.com, of course...

DSP Kernels (Complex FIR, Real FIR, Real Delayed LMS FIR)
http://motorola.com/SPS/PowerPC/AltiVec/CodeMain.html

Altivec PIM (Programming Interface Manual -- the C bindings)
http://a1008.g.akamai.net/7/1008/787/66cefa0933a341/www.motorola.com/SPS/PowerPC/teksupport/teklibrary/manuals/altivecpim.pdf

Altivec PEM (Programming Environtment Manual -- the assembly level docs)
http://a2016.g.akamai.net/7/2016/787/5087c1b5def3b1/www.motorola.com/SPS/PowerPC/teksupport/teklibrary/manuals/altivec_pem.pdf

>So these will presumably still work when there will fit more then 4
>floats in a reg?
>How do they do this? Or is it fixed at 4? In that case, vecor is a
>mis-nomer, should be vector4 OSLT.

  That's a good point.  I don't know if they ever plan on extending the number of elements per vector.  They might just decide to extend the number of vector registers and number of pipelines :)

>According to ANSI C, you want to loose precision.

  Well, yes.  That is what the compiler has to assume.  But the author may have just been silly when writing the code.  I've seen lots of cases of this when optimizing for PPC (since it is really bad at doing int/float conversions).  Needless casts between int/float can cost a lot.

-tim

  
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