Merged revisions 82646,82649-82650 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/branches/py3k

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  r82646 | mark.dickinson | 2010-07-08 18:23:40 +0100 (Thu, 08 Jul 2010) | 1 line

  In test_decimal, convert heuristic for skipping tests into an explicit skiplist.
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  r82649 | mark.dickinson | 2010-07-08 20:03:34 +0100 (Thu, 08 Jul 2010) | 1 line

  Fix a performance issue in Decimal.pow.  Thanks Stefan Krah for finding this.
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  r82650 | mark.dickinson | 2010-07-08 20:09:16 +0100 (Thu, 08 Jul 2010) | 1 line

  Fix misplaced exactness check that was causing unnecessary work in Decimal.__pow__.
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1 files changed, 12 insertions, 9 deletions

diff --git a/Lib/decimal.py b/Lib/decimal.py
index ecf0cd5..958b2f9 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -2044,12 +2044,14 @@ 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
@@ -2322,9 +2324,10 @@ class Decimal(object):
         # try for an exact result with precision +1
         if ans is None:
             ans = self._power_exact(other, context.prec + 1)
-            if ans is not None and result_sign == 1:
-                ans = _dec_from_triple(1, ans._int, ans._exp)
-            exact = True
+            if ans is not None:
+                if result_sign == 1:
+                    ans = _dec_from_triple(1, ans._int, ans._exp)
+                exact = True
 
         # usual case: inexact result, x**y computed directly as exp(y*log(x))
         if ans is None: