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## Re: code optimizations and numerical research

**From**: |
Brian Gough |

**Subject**: |
Re: code optimizations and numerical research |

**Date**: |
Tue, 17 May 2005 20:37:57 +0100 |

Peter Jay Salzman writes:
>* The man page claims that "-ffast-math" may produce wrong results for*
>* programs that depend on "an exact implementation of IEEE or ISO*
>* rules/specifications for math functions."*
>* *
>* What exactly does this vague sentence mean?*
The main problem is that Infs and NaNs are manipulated as finite
numbers in optimisations and comparisons with -ffast-math. e.g. you
can find that x-x==0 for x=Inf and other similar oddities. Some
programs use non-standard idioms like if(x!=x) for checking if x is
NaN.
--
Brian Gough
(GNU Scientific Library Maintainer)
p.s. don't forget to profile your program.
Network Theory Ltd,
Publishing "An Introduction to GCC" --- http://www.network-theory.co.uk/gcc/

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**Re: code optimizations and numerical research**,
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