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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.ada
Subject: Re: How to check a Float for NaN
Date: Sun, 11 May 2008 15:00:55 -0700
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anon@anon.org (anon) writes:
> If you look at my first post on this topic and change the 16#FF000000# 
> to 16#7F000000# (typo, forgot to adjust for the sign-bit) its basically 
> what I have done except that I use a 64-bit sign integer instead of the 
> Unsigned_64.  In order to save coding time, did not want to add the
> extra statements. Plus, if it for a final (it that time of the year) they 
> should be able add those lines.
[...]

You're using a value conversion.  This converts, for example, the
Float value 3.0 to the Long_Long_Integer value 3.  In your code, with
16#FF000000# changed to 16#7F000000#, this:

    T : Long_Long_Integer := Long_Long_Integer ( N ) ;
    ...
    if T > 16#7F000000# then
    ...

is essentially equivalent to this:

    if T > 2130706432.0 then

Try isNan(2.0E9) and isNan(3.0E9).

You need an Unchecked_Conversion.  You also need to make sure you
choose a floating-point and integer type of the same size, and to
allow for things like byte ordering (even if you're limiting the test
to systems that support IEEE floating-point, which is probably a
reasonable restriction since other floating-point formats may not
support NaNs at all).

-- 
Keith Thompson (The_Other_Keith) <kst-u@mib.org>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"