Re: +-Inf and NaN

Signaling NaNs are another matter.

But preventing, say, IEEEinf-IEEEinf from returning 0 is really important
in numeric code.

On Tue, Feb 20, 2024 at 7:40 PM Henry Baker <[email protected]> wrote:

> 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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