[Python-checkins] r51711 - in python/branches/release25-maint: Misc/NEWS Objects/intobject.c
tim.peters
python-checkins at python.org
Tue Sep 5 03:47:54 CEST 2006
Author: tim.peters
Date: Tue Sep 5 03:47:53 2006
New Revision: 51711
Modified:
python/branches/release25-maint/Misc/NEWS
python/branches/release25-maint/Objects/intobject.c
Log:
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.
Modified: python/branches/release25-maint/Misc/NEWS
==============================================================================
--- python/branches/release25-maint/Misc/NEWS (original)
+++ python/branches/release25-maint/Misc/NEWS Tue Sep 5 03:47:53 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.
@@ -127,7 +130,7 @@
- The __repr__ method of a NULL ctypes.py_object() no longer raises
an exception.
-- uuid.UUID now has a bytes_le attribute. This returns the UUID in
+- uuid.UUID now has a bytes_le attribute. This returns the UUID in
little-endian byte order for Windows. In addition, uuid.py gained some
workarounds for clocks with low resolution, to stop the code yielding
duplicate UUIDs.
@@ -286,7 +289,7 @@
- Bug #1002398: The documentation for os.path.sameopenfile now correctly
refers to file descriptors, not file objects.
-- The renaming of the xml package to xmlcore, and the import hackery done
+- The renaming of the xml package to xmlcore, and the import hackery done
to make it appear at both names, has been removed. Bug #1511497,
#1513611, and probably others.
Modified: python/branches/release25-maint/Objects/intobject.c
==============================================================================
--- python/branches/release25-maint/Objects/intobject.c (original)
+++ python/branches/release25-maint/Objects/intobject.c Tue Sep 5 03:47:53 2006
@@ -564,8 +564,14 @@
"integer division or modulo by zero");
return DIVMOD_ERROR;
}
- /* (-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)
return DIVMOD_OVERFLOW;
xdivy = x / y;
xmody = x - xdivy * y;
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