Re: [gentoo-amd64] gcc 4.1 + CFLAGS

[Paul de Vrieze]

On Saturday 10 June 2006 00:28, Hemmann, Volker Armin wrote:
> On Friday 09 June 2006 23:42, Vladimir G. Ivanovic wrote:
> > On Fri, 2006-06-09 at 16:14 -0500, Barry.SCHWARTZ@×××××××××××××.org
> >
> > wrote:
> > > Enough research has gone into writing code for IEEE floating point
> > > that I would not try to bypass it without a good reason. It’s there
> > > to be your friend.
> >
> > Performance is the reason we have hardware FPUs and -ffast-math.
>
> no, ffast-math is for the case, that you
>
> a) don't need accurate results
>
> b) the FPU is not fast enough
>
>
> since you can't say if you need accurate math for an app you did not
> wrote or examined, using ffast-math is highly dangerous. And sicne the
> hardware gets faster on an almost monthly basis, it is even less
> convincing why anybody should use it.

I completely agree. The gcc info page puts it this way:
     This option should never be 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.

In short there is a very good reason it is not on by default and may never 
be turned on by default.

Paul

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