changeset:   103010:31586a2f01b6
user:        Ethan Furman <ethan@stoneleaf.us>
date:        Fri Sep 02 15:50:21 2016 -0700
files:       Lib/enum.py
description:
issue23591: optimize _high_bit()


diff -r 12ce8e0413f1 -r 31586a2f01b6 Lib/enum.py
--- a/Lib/enum.py	Fri Sep 02 12:12:23 2016 +0200
+++ b/Lib/enum.py	Fri Sep 02 15:50:21 2016 -0700
@@ -784,13 +784,8 @@
 
 
 def _high_bit(value):
-    """return the highest bit set in value"""
-    bit = 0
-    while 'looking for the highest bit':
-        limit = 2 ** bit
-        if limit > value:
-            return bit - 1
-        bit += 1
+    """returns index of highest bit, or -1 if value is zero or negative"""
+    return value.bit_length() - 1 if value > 0 else -1
 
 def unique(enumeration):
     """Class decorator for enumerations ensuring unique member values."""