Re: +-Inf and NaN

A while ago I reported some experiments with 'signalling' Nan's, and
concluded that they were worthless, as there wasn't enough info left
at interrupt time to do anything interesting, and if you built the structures
needed to do something interesting, then you would still be better off
with an explicit check and explicitly branch to the corresponding code.

I came away from that experience with a really bad taste in my mouth
w.r.t. NaN's, so I would be very supportive of getting NaN's out of the
way of doing more important things.

-----Original Message-----
From: Camm Maguire <[email protected]>
Sent: Feb 20, 2024 3:58 PM
To: Robert Dodier <[email protected]>, <[email protected]>, <[email protected]>
Cc: <[email protected]>
Subject: [Maxima-discuss] +-Inf and NaN

Greetings! I know this has been discussed before, but I would like to
explore the possibility of defining these bit patterns as members of a
special type orthogonal to common-lisp::number. This is prompted by the
NaN blockage on the compiler optimizing (= a a) (or equivalent bindings)
to t, and indeed the common lisp spec appears to specify that eq implies
=. I think maxima tries to detect NaNs using (/= a a).

We also have the following charming behavior:

(typep nan 'long-float) ->t
(typep nan '(long-float 0) ->nil
(typep nan '(long-float * 0)) ->nil
(typep nan '(or (long-float 0) (long-float * 0))) ->nil

but the first and last types are of course identical.

If NaN was truly 'not a number', the numerical functions would trigger
an error on input only when compiled with safety, and might be arranged
to do likewise on return, so the signatures would remain the same but
the user could still access the values when compiling at (safety 0).
Thoughts?

Take care,
--
Camm Maguire [email protected]
==========================================================================
"The earth is but one country, and mankind its citizens." -- Baha'u'llah


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