[Python-Dev] Expert floats (original) (raw)

Aahz aahz at pythoncraft.com
Wed Mar 31 00:47:50 EST 2004

On Tue, Mar 30, 2004, Andrew P. Lentvorski, Jr. wrote:

My question is: Is it possible that a C implementation of Decimal would be almost as fast as native floating point in Python for reasonable digit lengths and settings? (ie. use native FP as an approximation and then do some tests to get the last digit right).

Basic answer: yes, for people not doing serious number crunching

This is similar to the long int/int unification. Long ints are slow, but things are okay as long as the numbers are within the native range. The hope would be that Decimal configurations which fit within the machine format are reasonably fast, but things outside it slow down.

Well, that won't happen. The long/int issue at least has compatibility at the binary level; binary/decimal conversions lead us right back to the problems that Decimal is trying to fix.

Please note that nowhere did I comment that creating such a C implementation of Decimal would be easy or even possible. ;)

Actually, the whole point of the Decimal class is that it's easy to implement. Once we agree on the API and semantics, converting to C should be not much harder than trivial.

Although I ended up dropping the ball, that's the whole reason I got involved with Decimal in the first place: the intention is that Decimal written in C will release the GIL. It will be an experiment in computational threading.

Aahz (aahz at pythoncraft.com) <*> http://www.pythoncraft.com/

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