Subject: Re: [linux-audio-user] amd vs p4
From: Steve Harris (S.W.Harris_AT_ecs.soton.ac.uk)
Date: Wed Feb 18 2004 - 13:49:11 EET
On Wed, Feb 18, 2004 at 01:20:30 +0100, Tim Blechmann wrote:
> > I'm not up-to-date on benchmarks so I cant comment, but just to
> > clarify the denormal thing in P4's is not a bug, its how you handle
> > denormals, the only difference is that the P4 takes longer to handle
> > them so you get away with it less often.
> >
> > Ideally DSP software would be written so that it never generates them,
> > but, erm, well, developers are lazy, y'know :)
> sure, denormals are not a bug, but the behaviour on dsp systems that
> aren't denormal-save is similar to a bug ;-)
>
> > On the P4 its possible that you can set some flags to use SSE
> > instructions instead of 387 and tell the SSE unit to never produce
> > denormals, but last time I tried it, gcc 3.something generated bad
> > code (illegal instructions).
> wait ... you imply that the sse unit doesn't produce denormals, so that
> a -march=sse _should_ solve all dsp user problems?
> i heard that gcc 3.2 produces illegal instructions, but that it's solved
> in gcc 3.3 ... can anyone confirm / deny this?
SSE /can/ be prevented from producing denormals, it probably doesnt by
default because it would violate the IEEE float spec.
- Steve
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