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From: Warren <ve3wwg@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: S'Is_nan or S'Is_inf?
Date: Mon, 19 Jul 2010 17:18:33 +0000 (UTC)
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Dmitry A. Kazakov expounded in
news:5xj0ja9xywto$.3ncqua6onpoa.dlg@40tude.net: 

> On Fri, 16 Jul 2010 22:35:14 +0000 (UTC), Warren wrote:
> IEEE representations have more than +Inf, -Inf and NaN. There are 
> other objects: +0, -0, denormalized numbers (see attribute 'Denorm).
> Some have dubious semantics:

Ya, I know about those.  As indicated in my other reply,
I did eventually figure out that if F /= F, then it is NaN  
(for some reason, I didn't see this at first).

> What are you trying to achieve? Because in automation we have the rule
> never ever let IEEE cripples slip through. Don't read them, don't
> write them, don't compute them.

In my Basic interpreter, I'll raise an error if you try to
use these IEEE values in an argument to a function or try to 
compute something with an operator (here NOT 'Valid is sufficient).  
However, if the expression result is one of these, I do allow 
it to be assigned to a [basic] variable.

So then the user needs a (basic) function to test if the
variable V is +/- infinity or NaN. So in basic, ISNAN(X)
returns 1 if NaN, else zero, for example.

In the C version of the interpreter, I relied upon C functions
for these tests. Ada clearly does not need these C functions, 
which is bliss for the Ada rewrite.

Thanks for everyone's help.

Warren