--- Raymond Toy wrote:
> Robert> I find CMUCL and GCL both have :IEEE-FLOATING-POINT in
> Robert> *FEATURES*, although they both barf on computations which
> Robert> would yield not-a-number or infinity.
>
> If you have an example of this barfing, please show it.
What I mean is that (/ 1.0 0.0), (/ 0.0 0.0), (* 1e300 1e300)
all yield error messages instead of a IEEE 754 result.
> By default, in CMUCL, things that would produce NaN or infinity
> signal errors. But you can change that so it does return NaN or
> infinity.
Excellent. Maxima should set the appropriate flags to
return NaN and infinity.
> Of course, all computations after that are likely to be useless.
Whether the result is useful can't be determined at
the level of the floating point computation itself.
> And it's likely maxima doesn't know what to do with NaN or infinity.
If Maxima could just step aside and let the cpu figure
out the result, that would be an improvement.
This applies to floating point comparisons as well
as arithmetic results.
We might want Maxima to make a correspondence between
floating point infinity and NaN and symbolic inf and,
I hope, symbolic nan. This implies a certain amount
of work.
> Robert> Maxima probably should try to work around the underlying
> Robert> Lisp's prohibition of special values.
>
> Which special values? NaN and infinity? CMUCL handles them fine.
Great. Presumably SBCL inherits CMUCL's floating point
mechanisms. Maybe someone can tell us what is possible
with Clisp and GCL.
Robert Dodier
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