Re: How to check a Float for NaN

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 22 May 2014 10:24:35 +0100, Simon Wright wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> On Thu, 22 May 2014 00:27:02 -0700 (PDT), jan.de.kruyf@gmail.com wrote:
> 
>>>       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.
> 
> This would also return False for +/-Inf, so if the OP wants specifically
> to check for NaN it wouldn't do. Can't think why they would, though.
> 
> GNAT says about "X in Long_Float'Range"
>    inf.adb:10:60: warning: explicit membership test may be optimized away

Looks like a bug, it may not be optimized away if Long_Float is IEEE 754.

>    inf.adb:10:60: warning: use 'Valid attribute instead

Hmm, reading RM 13.9.2 makes me believe that NaN's 'Valid should yield
True.

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