[Python-Dev] Strategy for converting the decimal module to C

[Nick Maclaren]

Georg Brandl <g.brandl at gmx.net> wrote:
>
> > Even then, we need to drop the concept of having the flags as counters
> > rather than booleans.
>
> Yes. Given that even Tim couldn't imagine a use case for counting the
> exceptions, I think it's sensible.

Well, I can.  There is a traditional, important use - tuning.

When such arithmetic is implemented in hardware, it is normal for
exceptional cases to be handled by interrupt, and that is VERY
expensive - often 100-1,000 times the cost of a single operation,
occasionally 10,000 times.  It then becomes important to know how
many of the things you got, to know whether it is worth putting
code in to avoid them or even using a different algorithm.

Now, it is perfectly correct to say that this does not apply to
emulated arithmetic and that there is no justification for such
ghastly implementations.  But, regrettably, almost all exception
handling on modern systems IS ghastly - at least by the standards
of the 1960s.

Whether you regard the use of Python for tuning code that is to be
run using hardware, where the arithmetic will be performance-
critical as important, is a matter of taste.  I don't :-)


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:  nmm1 at cam.ac.uk
Tel.:  +44 1223 334761    Fax:  +44 1223 334679