Re: Catching NaN .. not a number

["David C. Hoos, Sr." <david.c.hoos.sr@ada95.com>]

As I posted Saturday, May 5:

Catching NaN requires a three-way test, viz.:

if Value /= 0.0 and then (not (Value < 0.0)) and then (not (Value > 0.0))
then
   <Value is NaN>;
end if;

"Stephen Leake" <stephen.a.leake.1@gsfc.nasa.gov> wrote in message
news:uelu0on1n.fsf@gsfc.nasa.gov...
> Keith Thompson <kst@cts.com> writes:
>
> > f97stdi@dd.chalmers.se (Staffan Dittmer) writes:
> > > Did some calcualtions during the night and
> > > ended up with an output file full of NaN - due to
> > > overflow when calculating a factorial.
> > >
> > > A bit surprised by this since I thought a Constraint Error
> > > would be raised.
> >
> > An implementation isn't required to raise Constraint_Error on
> > floating-point overflow or division by zero.  See the
> > Machine_Overflows attribute.
> >
> > > So, how do I catch a NaN result ?
> >
> > I don't think there's a standard way to do so; see the documentation
> > for your implementation.
>
> X'Valid should catch it; see ARM 13.9.2
>
> And it works in GNAT 3.14a:
>
> with Ada.Text_IO; use Ada.Text_IO;
> procedure NAN
> is
>    Zero : Float := 0.0;
>    A_NAN : Float := 1.0 / Zero;
> begin
>   Put_Line ("A_NAN'Valid => " & Boolean'Image (A_Nan'Valid));
> end NAN;
>
> generates:
>
> A_NAN'Valid => FALSE
>
> --
> -- Stephe