Re: Catching NaN .. not a number

[Stephen Leake <stephen.a.leake.1@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