Alexander Belopolsky <belopol...@users.sourceforge.net> added the comment:
On Tue, May 11, 2010 at 9:07 PM, Daniel Stutzbach <rep...@bugs.python.org> wrote: > > Daniel Stutzbach <dan...@stutzbachenterprises.com> added the comment: > > On Tue, May 11, 2010 at 7:38 PM, Alexander Belopolsky > <rep...@bugs.python.org> wrote: >> Speaking of micro-optimizations, did you consider a better than naive >> algorithm for "Count the number of set bits in n" in your patch? >> .. > I considered it, but decided to stick with code readability and > portability. Speaking of readability, with a separate popcount() function, you can simply write nminusnumbits_ob = PyLong_FromLong(n - popcount(n)) and eliminate not only the loop, but also num_bits and tmp variables from math_factorial() The popcount function can be defined as a __builtin_popcount on GCC and your loop otherwise. > Counting the number of set bits is only done once per > factorial, so it's not on the critical path. > I agree, performance consideration are completely irrelevant here. Similarly, while unlikely to improve performance, I would prefer not to use any bit-trick implementation of ilog2 (in a separate function, of course) instead of calling floating point log2. In my head, an assignment of floating point result to an integer variable always raises a red flag. Another readability nit: for me k % 2 == 0 is a more readable check for even number than (k & 1) != 1. Performance-wise the two choices are the same, and either can be improved by combining k = (n + m) / 2 and k & 1 into one ldiv call. I have not tried to do it, but my gut feeling is that factorial_part_product() can benefit from passing semi-open rather than closed interval. (Also renaming n and m to start and stop in this case will help understanding.) ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue8692> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
