Re: What is acceptable for -ffast-math? (Was: associative law incombine)

[Linus Torvalds <torvalds at transmeta dot com>]

On Sun, 29 Jul 2001, Stephen L Moshier wrote:
>
> > > Floating point arithmetic, IEEE or otherwise, does not obey the
> > > associative or distributive laws.
> >
> > This is YOUR opinion.
>
> That is not just an opinion, it is simple arithmetic.

No, it's actually a very complex issue of representing classical
arithmetic with finite values. It's not "simple arithmetic" at all. In the
simple arithmetic, operations _are_ associative and distriubutive.

And what I'm really claiming is that until gcc is a full Artifical
Intelligence system, it cannot add information to a program.

In 99% of all cases, the information of the subtleties of floating point
arithmetic simply was never there in the program gcc tries to compile.
Why? Becuase the programmer didn't even _intend_ any of the subtleties, or
even knew about them.

Gcc trying to enforce them doesn't add any value.

> Further, GCC is supposed to be standards compliant by default.

That is a separate argument, and I don't think you'r enecessarily wrong on
that front. On the other hand, people are already used to having command
line switches for strict standards adherence, so I don't think that this
argument is necessarily a very strong one, more a matter of opinion.

Especially true since the standard you quote is a fairly recent one (has
it been finalized now?)

		Linus