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Re: How bad is fast-math?

On Wed, May 30, 2001 at 01:35:27AM +0200, Jean Francois Martinez wrote:
> On Wednesday 30 May 2001 01:02, Michael Meissner wrote:
> > On Wed, May 30, 2001 at 12:25:50AM +0200, Jean Francois Martinez wrote:
> > > According to the doc fast-math generates incorrect code.   Has the
> > > situation changed?   In case it has doc should be updated, in case it
> > > hasn't name should be changed and become something derogatory since there
> > > are people who see the fast in fast-math and use it without further
> > > investigation.   It is being used in aLinux distribution and I have seen
> > > it recommended in a Linux magazine
> >
> > In general, it depends on what you consider the correct code to be :-)
> >
> > If your code never encounters infinities and denormals, and never passes an
> > out of range argument to an intrinsic function, then -ffast-math will
> > certainly generate faster code on some machines.  I can't say how well that
> > matches up with the numeric code out there.  I would imagine many codes
> > don't stray into these dark corners (but then again, many do go into that
> > territory).
> Use in glibc would be certainly foolish.   And I think it is being done.

If it is being done in an unsafe manner, then you need to bring it up with the
glibc developers in the proper forum.

Michael Meissner, Red Hat, Inc.  (GCC group)
PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886, USA
Work:		phone: +1 978-486-9304
Non-work:	fax:   +1 978-692-4482

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