Mark Dickinson added the comment: Trent, many thanks for the report and analysis. The LOG1P_DROPS_ZERO_SIGN hackery was a result of a previous attempt to 'fix' the tests on another platform whose log1p didn't preserve zero signs. But now that this behaviour has emerged on OS X too, I think it might be time to fix this in the Python core code (i.e., add a workaround for the buggy OS behaviour) instead of trying to make the tests pass again.
Attached is a patch that adds a workaround for this on all platforms that have a system log1p. I was originally thinking of adding this workaround only on OS X (so as not to unnecessarily punish those platforms that get it right), but after running some timings (see below) it seems that the workaround is insignificant performance-wise, so we might as well keep things simple and add it on all platforms. Trent, if you have time, please could you try this patch on OS X 10.8 and see if it fixes all the test_cmath and test_math failures? Some timings on OS X 10.6. Current default branch (pass value directly onto system log1p): iwasawa:cpython mdickinson$ ./python.exe -m timeit -s 'from math import log1p; x = 2.3' 'log1p(x)' 10000000 loops, best of 3: 0.0685 usec per loop With the attached patch (do zero check, then pass value directly onto system log1p): iwasawa:cpython mdickinson$ ./python.exe -m timeit -s 'from math import log1p; x = 2.3' 'log1p(x)' 10000000 loops, best of 3: 0.0686 usec per loop ---------- Added file: http://bugs.python.org/file26884/log1p_sign_workaround.patch _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue15477> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
