[Python-checkins] cpython (2.7): Issue 13496: Fix bisect.bisect overflow bug for large collections.

[mark.dickinson]

http://hg.python.org/cpython/rev/709af2d0e862
changeset:   76325:709af2d0e862
branch:      2.7
parent:      76322:bf3b77722c9f
user:        Mark Dickinson <mdickinson at enthought.com>
date:        Sun Apr 15 16:43:19 2012 +0100
summary:
  Issue 13496: Fix bisect.bisect overflow bug for large collections.

files:
  Lib/test/test_bisect.py |   7 +++++++
  Misc/NEWS               |   3 +++
  Modules/_bisectmodule.c |  13 +++++++++++--
  3 files changed, 21 insertions(+), 2 deletions(-)


diff --git a/Lib/test/test_bisect.py b/Lib/test/test_bisect.py
--- a/Lib/test/test_bisect.py
+++ b/Lib/test/test_bisect.py
@@ -122,6 +122,13 @@
         self.assertRaises(ValueError, mod.insort_left, [1, 2, 3], 5, -1, 3),
         self.assertRaises(ValueError, mod.insort_right, [1, 2, 3], 5, -1, 3),
 
+    def test_large_range(self):
+        # Issue 13496
+        mod = self.module
+        data = xrange(sys.maxsize-1)
+        self.assertEqual(mod.bisect_left(data, sys.maxsize-3), sys.maxsize-3)
+        self.assertEqual(mod.bisect_right(data, sys.maxsize-3), sys.maxsize-2)
+
     def test_random(self, n=25):
         from random import randrange
         for i in xrange(n):
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -48,6 +48,9 @@
 Library
 -------
 
+- Issue #13496: Fix potential overflow in bisect.bisect algorithm when applied
+  to a collection of size > sys.maxsize / 2.
+
 - Issue #14399: zipfile now recognizes that the archive has been modified even
   if only the comment is changed.  As a consequence of this fix, ZipFile is now
   a new style class.
diff --git a/Modules/_bisectmodule.c b/Modules/_bisectmodule.c
--- a/Modules/_bisectmodule.c
+++ b/Modules/_bisectmodule.c
@@ -21,7 +21,13 @@
             return -1;
     }
     while (lo < hi) {
-        mid = (lo + hi) / 2;
+        /* The (size_t)cast ensures that the addition and subsequent division
+           are performed as unsigned operations, avoiding difficulties from
+           signed overflow.  (See issue 13496.) */
+        printf("lo: %d\n", lo);
+        printf("hi: %d\n", hi);
+        printf("mid: %d\n", mid);
+        mid = ((size_t)lo + hi) / 2;
         litem = PySequence_GetItem(list, mid);
         if (litem == NULL)
             return -1;
@@ -122,7 +128,10 @@
             return -1;
     }
     while (lo < hi) {
-        mid = (lo + hi) / 2;
+        /* The (size_t)cast ensures that the addition and subsequent division
+           are performed as unsigned operations, avoiding difficulties from
+           signed overflow.  (See issue 13496.) */
+        mid = ((size_t)lo + hi) / 2;
         litem = PySequence_GetItem(list, mid);
         if (litem == NULL)
             return -1;

-- 
Repository URL: http://hg.python.org/cpython