| msg136022 - (view) |
Author: Stefan Krah (skrah) *  |
Date: 2011-05-15 08:28 |
| I found another performance issue in _power_exact: >>> Decimal(4) ** Decimal("-1.2e-999999999") ^CTraceback (most recent call last): File "", line 1, in File "/home/stefan/pydev/cpython/Lib/decimal.py", line 2343, in __pow__ ans = self._power_exact(other, context.prec + 1) File "/home/stefan/pydev/cpython/Lib/decimal.py", line 2098, in _power_exact ten_pow = 10**-ye KeyboardInterrupt This one is in the power operation in line 2098. There are several other places where huge integer powers are calculated if 'ye' is sufficiently large. |
|
|
| msg136044 - (view) |
Author: Mark Dickinson (mark.dickinson) * |
Date: 2011-05-15 18:37 |
| Thanks for the report; I'll try to find some time to look at this. This isn't the first time that I've thought that it might be better just to abandon the aim of getting correctly-rounded results for pow. |
|
|
| msg136524 - (view) |
Author: Mark Dickinson (mark.dickinson) * |
Date: 2011-05-22 13:51 |
| Here's a patch. Stefan, could you please review? |
|
|
| msg136536 - (view) |
Author: Mark Dickinson (mark.dickinson) * |
Date: 2011-05-22 15:10 |
| Here's a slightly improved version that adds guards against computing 10**ye for large ye in the case y < 0, ye > 0. |
|
|
| msg137652 - (view) |
Author: Roundup Robot (python-dev)  |
Date: 2011-06-04 17:14 |
| New changeset c3fe54781244 by Mark Dickinson in branch 'default': Issue #12080: Fix a performance issue in Decimal._power_exact that causes some corner-case Decimal.__pow__ calls to take an unreasonably long time. http://hg.python.org/cpython/rev/c3fe54781244 |
|
|
| msg137653 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2011-06-04 17:24 |
| New changeset 78d79499e7de by Mark Dickinson in branch '2.7': Issue #12080: Fix a performance issue in Decimal._power_exact that caused some corner-case Decimal.__pow__ calls to take an unreasonably long time. http://hg.python.org/cpython/rev/78d79499e7de |
|
|
| msg137654 - (view) |
Author: Mark Dickinson (mark.dickinson) * |
Date: 2011-06-04 17:25 |
| Fixed for 3.3 and 2.7. |
|
|
| msg137655 - (view) |
Author: Stefan Krah (skrah) * |
Date: 2011-06-04 17:59 |
| Mark Dickinson <report@bugs.python.org> wrote: > Here's a patch. Stefan, could you please review? Mark, sorry for not replying earlier. The patch looks great. I've also tested the patch in practice: I ran 700,000,000 random tests with an exponent range of [-999999999, 999999999]. This took three days. Without the patch, this would have been impossible; the range had to be restricted to [-9999, 9999]. Unfortunately I got sidetracked reviewing the rest of the function (today I started out on a mechanical proof of the nth-root part). I *did* review the changes though, and I think they are correct. |
|
|