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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: How to check a Float for NaN
Date: Thu, 22 May 2014 10:09:02 +0200
Organization: cbb software GmbH
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Date: 2014-05-22T10:09:02+02:00
List-Id: <comp.lang.ada>

On Thu, 22 May 2014 00:27:02 -0700 (PDT), jan.de.kruyf@gmail.com wrote:

> On Wednesday, April 30, 2008 10:36:21 PM UTC+2, Jerry wrote:
> 
>> 
>> Check this out:
>> 
>> function Is_NaN(x : Long_Float) return Boolean is
>> begin
>>     return x /= x;
>> end Is_NaN;
>> 
>> A couple of minutes on Wikipedia saves the day. From
>> http://en.wikipedia.org/wiki/NaN#NaN_encodings:
>> 
>> "A NaN does not compare equal to any floating-point number or NaN,
>> even if the latter has an identical representation. One can therefore
>> test whether a variable has a NaN value by comparing it to itself."
>> 
>> Jerry
> 
> This worked on the Gnat compiler, this code
> 
>       if Cos_Theta /= Cos_Theta then
> 	 Gct.Trace (Debug_Str, "cos_theta is NaN******");
>       else
> 	 Gct.Trace (Debug_Str, "cos_theta : " & Long_Float'Image (Cos_Theta)); 
>       end if;
> 
> gives this in the log:
> 
> [MATH3D.DEBUG] 1/372 cos_theta is NaN****** (2014-05-22 09:23:24.155)(loc: math3d.adb:129)
> 
> Hope it helps someone;

You could simply use range check:

   X in Long_Float'Range

NaN is not a number and thus outside the range.

However, for technical computations, it is advisory to turn IEEE semantics
off. Fortunately there is a very simple way to do so in Ada:

   subtype Real_Long_Float is Long_Float range Long_Float'Range;

Use this instead of Long_Float and you will never have NaN, +/-Inf again.
Constraint_Error will propagate instead.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de