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| author | Mark Dickinson <dickinsm@gmail.com> | 2010-07-08 19:03:34 (GMT) |
|---|---|---|
| committer | Mark Dickinson <dickinsm@gmail.com> | 2010-07-08 19:03:34 (GMT) |
| commit | a123631a5ca464c99faf039ee5c74ec9025d5d64 (patch) | |
| tree | 93f70adf2ec66d91d1377eeea682eef31e60017a /Lib | |
| parent | f48ea7c2a950c81b98c6e689fc51c99598546bb4 (diff) | |
| download | cpython-a123631a5ca464c99faf039ee5c74ec9025d5d64.zip cpython-a123631a5ca464c99faf039ee5c74ec9025d5d64.tar.gz cpython-a123631a5ca464c99faf039ee5c74ec9025d5d64.tar.bz2 | |
Fix a performance issue in Decimal.pow. Thanks Stefan Krah for finding this.
Diffstat (limited to 'Lib')
| -rw-r--r-- | Lib/decimal.py | 14 | ||||
| -rw-r--r-- | Lib/test/decimaltestdata/extra.decTest | 13 |
2 files changed, 21 insertions, 6 deletions
diff --git a/Lib/decimal.py b/Lib/decimal.py index 828027c..71408a8 100644 --- a/Lib/decimal.py +++ b/Lib/decimal.py @@ -2047,12 +2047,14 @@ class Decimal(object): # case where xc == 1: result is 10**(xe*y), with xe*y # required to be an integer if xc == 1: - if ye >= 0: - exponent = xe*yc*10**ye - else: - exponent, remainder = divmod(xe*yc, 10**-ye) - if remainder: - return None + xe *= yc + # result is now 10**(xe * 10**ye); xe * 10**ye must be integral + while xe % 10 == 0: + xe //= 10 + ye += 1 + if ye < 0: + return None + exponent = xe * 10**ye if y.sign == 1: exponent = -exponent # if other is a nonnegative integer, use ideal exponent diff --git a/Lib/test/decimaltestdata/extra.decTest b/Lib/test/decimaltestdata/extra.decTest index 2640842..fce8435 100644 --- a/Lib/test/decimaltestdata/extra.decTest +++ b/Lib/test/decimaltestdata/extra.decTest @@ -213,7 +213,20 @@ extr1658 shift 1234567 3 -> 7000 extr1659 shift 1234567 4 -> 0 extr1660 shift 1234567 5 -> NaN Invalid_operation +-- Cases where the power function was impossibly slow to determine that the +-- result is inexact. Thanks Stefan Krah for identifying this problem. +precision: 16 +maxExponent: 999999999 +minExponent: -999999999 +extr1700 power 10 1e-999999999 -> 1.000000000000000 Inexact Rounded +extr1701 power 100.0 -557.71e-742888888 -> 1.000000000000000 Inexact Rounded +extr1702 power 10 1e-100 -> 1.000000000000000 Inexact Rounded +-- A couple of interesting exact cases for power. Note that the specification +-- requires these to be reported as Inexact. +extr1710 power 1e375 56e-3 -> 1.000000000000000E+21 Inexact Rounded +extr1711 power 10000 0.75 -> 1000.000000000000 Inexact Rounded +extr1712 power 1e-24 0.875 -> 1.000000000000000E-21 Inexact Rounded -- Tests for the is_* boolean operations precision: 9 |