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@hetp.u-net.com
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