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Re: -ffast-math option at compling octave in FreeBSD ports ?

From: Thomas Weber
Subject: Re: -ffast-math option at compling octave in FreeBSD ports ?
Date: Sun, 7 Dec 2008 10:30:15 +0100
User-agent: Mutt/1.5.18 (2008-05-17)

On Sun, Dec 07, 2008 at 05:12:29PM +0900, Tatsuro MATSUOKA wrote:
> Hello
> In an octave thread in Japan, there was a report that asked the meaning 
> -ffast-math option in FreeBSD ports.
> It will be glad for me if there are some peple who will give me information 
> about it.

It tries to exploit some processor features for faster mathematic
functions, but breaks IEEE 754 for that. Citing gcc's manual:

This option causes the preprocessor macro __FAST_MATH__ to be defined.
This option is not turned on by any `-O' option since it can result in
incorrect output for programs which depend on an exact implementation of
IEEE or ISO rules/specifications for math functions. It may, however,
yield faster code for programs that do not require the guarantees of
these specifications.

For details, you are probably best off asking on gcc's list.

The obvious question is now whether Octave and all used libraries work
with -ffast-math. Sorry, I have no idea about that.


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