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Re: How bad is fast-math?


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).

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


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