Re: GNAT Optimization of Constant Expressions

["Randy Brukardt" <randy@rrsoftware.com>]

"Georg Bauhaus" <bauhaus@futureapps.de> wrote in message
news:1179487665.6721.7.camel@localhost.localdomain...
> On Thu, 2007-05-17 at 18:38 -0500, Randy Brukardt wrote:
>
> >  Ada has fairly strict requirements on accuracy that C and
> > Fortran don't have. An optimizer shouldn't be providing the *wrong*
answer
> > in order to make code fast;
>
> An Apple employee once recommended using the then new FPT
> optimizations and to see whether the optimized program will meet
> the expectations. ("You can always sell speed".) So maybe accurate
> computation is a far reaching requirement for some software
> markets.

I think it is generally agreed these days that the Ada accuracy requirements
were a mistake, because they put Ada at a competitive disadvantage compared
to other languages for floating point math. Indeed, that is why they were
moved into "strict mode" in Ada 95. The problem is, faced with the need to
implement strict mode anyway, implementers have tended to avoid implementing
relaxed modes, because extra modes simply doubles the implementation and
testing effort - the fewer modes the better. And the argument is "who wants
less accuracy anyway?".

We talked briefly about dropping the accuracy requirements altogether this
time, but its obvious that would screw anyone that was depending on them.
And that didn't seem like a good idea. So Ada is rather stuck with its
slower but predictably accurate math. (In practice, this really only matters
in programs with intensive FP, like the OP's example.)

                      Randy.