From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,734832b8ad479964
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2001-05-07 14:45:34 PST
Path: 
 newsfeed.google.com!newsfeed.stanford.edu!canoe.uoregon.edu!hammer.uoregon.edu!skates!not-for-mail
From: Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: Catching NaN .. not a number
Date: 07 May 2001 17:40:36 -0400
Organization: NASA Goddard Space Flight Center
Message-ID: <uelu0on1n.fsf@gsfc.nasa.gov>
References: <9d1eai$3nf$1@eol.dd.chalmers.se> <yecg0ej5uub.fsf@king.cts.com>
NNTP-Posting-Host: anarres.gsfc.nasa.gov
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: skates.gsfc.nasa.gov 989272566 2762 128.183.220.71 (7 May 2001
 21:56:06 GMT)
X-Complaints-To: dscoggin@cne-odin.gsfc.nasa.gov
NNTP-Posting-Date: 7 May 2001 21:56:06 GMT
User-Agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/20.6
Xref: newsfeed.google.com comp.lang.ada:7288
Date: 2001-05-07T21:56:06+00:00
List-Id: <comp.lang.ada>

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