[Python-checkins] r51715 - in python/branches/release24-maint: Misc/NEWS Objects/intobject.c
python-checkins at python.org
Tue Sep 5 04:00:52 CEST 2006
Date: Tue Sep 5 04:00:47 2006
New Revision: 51715
Merge rev 51711 from the 2.5 branch.
i_divmod(): As discussed on Python-Dev, changed the overflow
checking to live happily with recent gcc optimizations that
assume signed integer arithmetic never overflows.
--- python/branches/release24-maint/Misc/NEWS (original)
+++ python/branches/release24-maint/Misc/NEWS Tue Sep 5 04:00:47 2006
@@ -12,6 +12,9 @@
Core and builtins
+- Overflow checking code in integer division ran afoul of new gcc
+ optimizations. Changed to be more standard-conforming.
- Patch #1541585: fix buffer overrun when performing repr() on
a unicode string in a build with wide unicode (UCS-4) support.
--- python/branches/release24-maint/Objects/intobject.c (original)
+++ python/branches/release24-maint/Objects/intobject.c Tue Sep 5 04:00:47 2006
@@ -478,8 +478,14 @@
"integer division or modulo by zero");
- /* (-sys.maxint-1)/-1 is the only overflow case. */
- if (y == -1 && x < 0 && x == -x)
+ /* (-sys.maxint-1)/-1 is the only overflow case. x is the most
+ * negative long iff x < 0 and, on a 2's-complement box, x == -x.
+ * However, -x is undefined (by C) if x /is/ the most negative long
+ * (it's a signed overflow case), and some compilers care. So we cast
+ * x to unsigned long first. However, then other compilers warn about
+ * applying unary minus to an unsigned operand. Hence the weird "0-".
+ if (y == -1 && x < 0 && (unsigned long)x == 0-(unsigned long)x)
xdivy = x / y;
xmody = x - xdivy * y;
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