"Martin v. Löwis" <[EMAIL PROTECTED]> writes: > Kristján V. Jónsson schrieb: >> I can't see how this situation is any different from the re-use of >> low ints. There is no fundamental law that says that ints below 100 >> are more common than other, yet experience shows that this is so, >> and so they are reused. > > There are two important differences: > 1. it is possible to determine whether the value is "special" in > constant time, and also fetch the singleton value in constant > time for ints; the same isn't possible for floats.
I don't think you mean "constant time" here do you? I think most of the code posted so far has been constant time, at least in terms of instruction count, though some might indeed be fairly slow on some processors -- conversion from double to integer on the PowerPC involves a trip off to memory for example. Even so, everything should be fairly efficient compared to allocation, even with PyMalloc. > 2. it may be that there is a loss of precision in reusing an existing > value (although I'm not certain that this could really happen). > For example, could it be that two values compare successful in > ==, yet are different values? I know this can't happen for > integers, so I feel much more comfortable with that cache. I think the only case is that the two zeros compare equal, which is unfortunate given that it's the most compelling value to cache... I don't know a reliable and fast way to distinguish +0.0 and -0.0. Cheers, mwh -- The bottom tier is what a certain class of wanker would call "business objects" ... -- Greg Ward, 9 Dec 1999 _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
