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Re: nan -ffast-math

From: Jim Wilson <wilson at specifixinc dot com>
To: antonio dot bleile at askvisual dot de
Cc: gcc-bugs at gcc dot gnu dot org
Date: Thu, 05 Feb 2004 11:45:08 -0800
Subject: Re: nan -ffast-math
References: <4022205E.2000704@askvisual.de>

Antonio Bleile wrote:

When compiled without any flag, like "gcc bug.c"
the output of the program will be "NAN != 0.0".
When compiled with "gcc bug.c -ffast-math"
the output is "NAN == 0.0", which is, in my opinion,
wrong

This is what -ffast-math is desgined to do. See the documentation for this option.

-ffast-math results in faster FP code by making potentially unsafe simplifying assumptions, such as pretending that NaNs and Infinities don't exist. If your code requires NaNs and Infinities to work, then you can't use the -ffast-math option.

Recent gcc versions split -ffast-math into several suboptions, one of which is -ffinite-math-only, so you can choose whether you want NaNs and Infinities to work, while still getting the other benefits of -ffast-math. -- Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com

References:
- nan -ffast-math
  - From: Antonio Bleile

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