changeset:   102826:370bbeba21b3
branch:      2.7
parent:      102815:3e0f8acf786c
user:        Mark Dickinson <dickinsm@gmail.com>
date:        Sun Aug 21 10:59:48 2016 +0100
files:       Misc/NEWS Objects/longobject.c
description:
Issue #25604: Fix bug in integer true division that could have resulted in off-by-one-ulp results in unusual cases.


diff -r 3e0f8acf786c -r 370bbeba21b3 Misc/NEWS
--- a/Misc/NEWS	Sun Aug 21 00:18:49 2016 -0400
+++ b/Misc/NEWS	Sun Aug 21 10:59:48 2016 +0100
@@ -10,6 +10,10 @@
 Core and Builtins
 -----------------
 
+- Issue #25604: Fix a minor bug in integer true division; this bug could
+  potentially have caused off-by-one-ulp results on platforms with
+  unreliable ldexp implementations.
+
 - Issue #27473: Fixed possible integer overflow in str, unicode and bytearray
   concatenations and repetitions.  Based on patch by Xiang Zhang.
 
diff -r 3e0f8acf786c -r 370bbeba21b3 Objects/longobject.c
--- a/Objects/longobject.c	Sun Aug 21 00:18:49 2016 -0400
+++ b/Objects/longobject.c	Sun Aug 21 10:59:48 2016 +0100
@@ -3315,9 +3315,9 @@
     /* Round by directly modifying the low digit of x. */
     mask = (digit)1 << (extra_bits - 1);
     low = x->ob_digit[0] | inexact;
-    if (low & mask && low & (3*mask-1))
+    if ((low & mask) && (low & (3U*mask-1U)))
         low += mask;
-    x->ob_digit[0] = low & ~(mask-1U);
+    x->ob_digit[0] = low & ~(2U*mask-1U);
 
     /* Convert x to a double dx; the conversion is exact. */
     dx = x->ob_digit[--x_size];