On Friday 09 June 2006 14:13, Ian McCulloch wrote:
> On Fri, 9 Jun 2006, Vladimir G. Ivanovic wrote:
> > On Fri, 2006-06-09 at 07:47 +0200, Michael Weyershäuser wrote:
> > > I don't recommend -ffast-math on a global basis (or at all), it
> > > gets you right where the Pentium fdiv bug brought us some years
> > > ago: floating point operations will be faster, but they could get a
> > > wrong result in some occasions...
> >
> > Linus seems to use -ffast-math:
> > http://gcc.gnu.org/ml/gcc/2001-07/msg02150.html. At least in 2001 he
> > did.
>
> I use it too, in my numerical simulations of the Schroedigner equation,
> I think it is fairly standard in the numerics community.  My
> understanding is that it results in a fairly consistent and predictable
> loss of precision for some operations, nothing like the catastrophic
> *errors* in the the intel fdiv bug.  Of course, for algorithms that are
> sensitive to precision, it can (and does) cause problems.

And all please remember that there are fairly easy equasions that can be 
very numerically  unstable. In such cases every bit of precision counts. 
Just do not enable it globally. If packages can use it, they can enable 
it themselves.

Paul

-- 
Paul de Vrieze
Gentoo Developer
Mail: pauldv@g.o
Homepage: http://www.devrieze.net