Re: Compile-time floating-point expressions and subsequent detection of possible overflows etc -- during the compile-time stage.

[leon zadorin <leonleon77 at gmail dot com>]

On 11/2/11, Andrew Haley <aph@redhat.com> wrote:
> On 11/02/2011 09:01 AM, Vincent Lefevre wrote:
>> In ISO C99, I don't think the compiler is allowed to replace a
>> floating expression with an underflow or overflow by its result
>> at compile time.
>
> But surely the "as if" rule applies here: if no conforming program
> can tell the difference, a transformation is allowed.
>
> Andrew.
>

I dont think that this is the point i am making... Gcc allows certain
optimization options eg -Ofast (4.6) where -ffast-math (even prior to
4.6), and some other, unsafe wrt pedantic standard definitions,
optimization options become available (including, i think
floating-point constant folding opportunities).

I am very happy with such options by the way so the question was not
about standard compliance (hence my original statement about the said
compile-time calculations being done under certain conditions, not all
the time and having nothing to do with c++03/11 standard
specifications).

I am saying that having such, great, otimization options available it
would be super-helpful if there was a way to have a diagnostic/warning
about compile-time calculations producing non-finite floating point
values (whether via lib mpfr or otherwise).

Regards Leon Zadorin.