[linux-audio-dev] interesting post from vst-plugins on float/int

Steve Harris S.W.Harris at ecs.soton.ac.uk
Tue Sep 17 10:52:16 UTC 2002

On Tue, Sep 17, 2002 at 11:49:26 +0200, Frank Neumann wrote:
> PS: No, I haven't been doing any Linux assembly programming yet. I only
> wondered every now and then how much performance one could get out of
> some of the existing Linux soundapps if there were optimized versions of
> such programs for certain CPUs.

>From experimenting with the intel vecorising compiler I would estimate you
could get 10-30% speed increase over gcc 2.96, for inner loops. I think
gcc 3 does a better job, and maybe even does some 3dNow vectorisation?

the vector instructions (SSE, 3DNow and Altivec etc.) are mostly useful
when you have parallel streams to be processed identically, but you can
also get wins just by dropping in vec. instructions inplace of float
equivalents as they are sometimes less accruate, but faster and have
common branch avoiding instructions (eg. min and max).

I think there is some cost in switching between float mode and vector mode
(on x86, probably not powerpc), and I dont know how high that is.

- Steve

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