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Subject: Re: [boost] several messages
From: Robert Ramey (ramey_at_[hidden])
Date: 2012-08-20 13:43:53

Paul A. Bristow wrote:
> William Kahan and the rest of the IEE754 designers wisely built in
> the concept of NotANumber. It provides protection against spurious,
> zero-information results.
> And, as we have discovered in writing functions and distributions in
> Boost.Math, it is a big simplification if all number systems also
> support a NaN concept, however it is implemented.

This is a topic which I'm curious about. I would have thought that
code which either produces or uses a NaN should always throw
an exception. But this is not the case - though apparently it's
a compile time option in some environments. What is the
reasoning behind this design? I would think that plowing
forward with an invalid result would always be a bad idea.
Then only thing I could think of was at the time (ca 1984)
makiing a hardware interrupt was too complicated - on
an alread complicated hardware spec (sub normal values, etc.)
and a software implemntation was considered too slow and
didn't work with fortran. I'm just curious about this, BTW
we once had an opportunity to have Kahan himself speak
a Boost Con but it didn't work out. Oh Well

Robert Ramey

> Paul
> ---
> Paul A. Bristow,
> Prizet Farmhouse, Kendal LA8 8AB UK
> +44 1539 561830 07714330204
> pbristow_at_[hidden]
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