Feature Requests item #1087418, was opened at 2004-12-18 00:22 Message generated for change (Comment added) made by rhettinger You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=355470&aid=1087418&group_id=5470
Category: None Group: None Status: Open Resolution: None >Priority: 4 Submitted By: Gregory Smith (gregsmith) >Assigned to: Nobody/Anonymous (nobody) Summary: long int bitwise ops speedup (patch included) Initial Comment: The 'inner loop' for applying bitwise ops to longs is quite inefficient. The improvement in the attached diff is - 'a' is never shorter than 'b' (result: only test 1 loop index condition instead of 3) - each operation ( & | ^ ) has its own loop, instead of switch inside loop - I found that, when this is done, a lot of things can be simplified, resulting in further speedup, and the resulting code is not very much longer than before (my libpython2.4.dll .text got 140 bytes longer). Operations on longs of a few thousand bits appear to be 2 ... 2.5 times faster with this patch. I'm not 100% sure the code is right, but it passes test_long.py, anyway. ---------------------------------------------------------------------- >Comment By: Raymond Hettinger (rhettinger) Date: 2005-01-07 01:54 Message: Logged In: YES user_id=80475 Patch Review ------------ On Windows using MSC 6.0, I could only reproduce about a small speedup at around 300 bits. While the patch is short, it adds quite a bit of complexity to the routine. Its correctness is not self-evident or certain. Even if correct, it is likely to encumber future maintenance. Unless you have important use cases and feel strongly about it, I think this one should probably not go in. An alternative to submit a patch that limits its scope to factoring out the innermost switch/case. I tried that and found that the speedup is microscopic. I suspect that that one unpredictable branch is not much of a bottleneck. More time is likely spent on creating z. ---------------------------------------------------------------------- Comment By: Gregory Smith (gregsmith) Date: 2005-01-03 14:54 Message: Logged In: YES user_id=292741 I originally timed this on a cygwin system, I've since found that cygwin timings tend to be strange and possibly misleading. On a RH8 system, I'm seeing speedup of x3.5 with longs of ~1500 bits and larger, and x1.5 speedup with only about 300 bits. Times were measured with timeit.Timer( 'a|b', 'a=...; b=...') Increase in .text size is likewise about 120 bytes. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=355470&aid=1087418&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
