[PlanetCCRMA] Pentium-4 and denormal numbers on planetccrma

Fernando Lopez-Lezcano nando@ccrma.Stanford.EDU
Wed Jan 12 10:11:01 2005

On Wed, 2005-01-12 at 05:45, andersvi@extern.uio.no wrote:
> Question is whether these switches (without the -mcpu=pentium4
> switch), or another solution to the problem, can be used in
> general for the whole planet-distribution?  With not much
> knowledge about denormal numbers, I guess all "realtime" apps
> might suffer from the same problem.  Jack, softsynths, plugins,
> etc.
> One use of planetccrma is to make installing precompiled audio
> and video-apps easy.  This problem brings at least me back to
> stage 1.

Agreed. When I did some research on this I finally decided that the
individual applications need to be fixed to handle this. 

The fix that Steve posted would work only if the application is compiled
with sse, and not all cpus have sse instructions, so I don't think I
should use this (well, probably only very very old ones). I also think I
read somewhere that the compile does not necessarily deal with sse very
well (again, maybe older versions). 

What is needed is app writers to id the places where the problem is
happening and insert code that will zero the denormals. 

This is also happening in freeverb. I think it does have denormal
handling code but somewhoe it is not working as it should. 

-- Fernando

> >>> On Wed, 12 Jan 2005 11:40:18 +0000, Steve Harris <S.W.Harris@ecs.soton.ac.uk> said:
> >> The fix was to recompile pd and the percolate-lib with
> >> 
> >> -mcpu=pentium4 -mfpmath=sse -msse
> >> 
> >> included in CFLAGS (not sure whether "-mcpu=pentium4" actually
> >> was necessary).
> >> 
> >> Ive started recompiling various externals and other things with
> >> the flags included.  Im not sure, but wouldnt this be a problem
> >> with all apps running loops calculating numbers around zero
> >> somewhere.  Would it be a solution to compile coming upgrades at
> >> planetccrma with these same flags?
> S> 
> S> You dont need -mcpu=pentium4. It will help P4's, and Athlon
> S> XP's and PIII's to a lesser extent, but it will not work on pre-XP Athlons
> S> or Pentium II's and older, or chips by most other manufacturers.
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