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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: How to check a Float for NaN
Date: Mon, 5 May 2008 13:49:25 -0700 (PDT)
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Date: 2008-05-05T13:49:25-07:00
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On May 5, 11:23 am, Martin Krischik <krisc...@users.sourceforge.net>
wrote:
> Jerry wrote:
> > How would one check a Float or Long_Float if it has value NaN? The
> > only ways that I can come up with are to import a C function (isnan, I
> > think) or to write Long_Float'image(Some_Float) to a string and
> > examine the first three characters to see if they are "NaN" (and that
> > seems to be a GNAT implementation choice so might not be portable,
> > which is OK for my use).
>
> How about an Unchecked Conversion to an Unsigned_64 and comparing
>
> >2#0111_1111_1111_0000_0000_0000_0000_0000#
>
> Note that it's '>' as 2#0111_1111_1111_0000_0000_0000_0000_0000# is positive
> infinity.

Any negative float (including negative infinity) would be > than the
binary number you give, since the leftmost bit (sign bit) would be 1.
I think you need to clear the sign bit first, then your comparison
will work:

  Is_NaN := (To_Unsigned_64(X) and not
              2#1000_0000_0000_0000_0000_0000_0000_0000#)
             > 2#0111_1111_1111_0000_0000_0000_0000_0000#;

But I haven't tried it.

                                  -- Adam