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Newsgroups: comp.lang.ada
Date: Thu, 22 May 2014 00:27:02 -0700 (PDT)
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Subject: Re: How to check a Float for NaN
From: jan.de.kruyf@gmail.com
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Xref: news.eternal-september.org comp.lang.ada:19967
Date: 2014-05-22T00:27:02-07:00
List-Id: <comp.lang.ada>

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;

Cheers,

j.