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RE: -ffast-math and gfortran
- From: Toon Moene <toon at moene dot indiv dot nluug dot nl>
- To: fortran at gcc dot gnu dot org, ronyoung8 at verizon dot net
- Date: Mon, 05 Jun 2006 15:21:23 +0200
- Subject: RE: -ffast-math and gfortran
> HP floating-point guide for HP Integrity servers
> http://h21007.www2.hp.com/dspp/tech/tech_TechDocumentDetailPage_IDX/1,1701,8359,00.html
I cannot access this page currently, because my X Window implementation
(Debian/testing) doesn't work at the moment; I'll look into it as soon
as that works again, because:
> Very good web page on floating point from HP. Includes a flow diagram on how
> to decide what floating point options to use for a given problem.
Yep, that would be my ultimate goal. However, that's more like a summer
project (I can normally get 6 weeks off during the summer season).
> It has the best explanation of the cx-limited-range option I've seen. It
> really shows what the problems are. If you really want to use this option,
> the compiler needs a #pragma to shut it off for some parts of the code.
If you cannot be sure that the divisors of complex division do not always
have a norm less than the square root of FLT_MAX and more than the square
root of FLT_MIN, then yes, you have to be careful.
> It would be nice to have a flow diagram like this in the gfortran
> documentation.
I agree. What's missing is a guide for the user that details what
s/he has to know about his/her program to be sure that
-funsafe-math-optimizations won't generate surprises.
Cheers,
--
Toon Moene - e-mail: toon@moene.indiv.nluug.nl - phone: +31 346 214290
Saturnushof 14, 3738 XG Maartensdijk, The Netherlands
A maintainer of GNU Fortran 95: http://gcc.gnu.org/fortran/
Gfortran At Work: http://mysite.verizon.net/serveall/moene.pdf