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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.
This commit is contained in:
Tim Peters 2006-09-05 01:47:53 +00:00
parent 3467352fe2
commit cbdd350dd7
2 changed files with 13 additions and 4 deletions
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7
Misc/NEWS
View File

@ -12,6 +12,9 @@ What's New in Python 2.5?
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 @@ Library
- 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 @@ Library
- 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.

10
Objects/intobject.c
View File

@ -564,8 +564,14 @@ i_divmod(register long x, register long y,
"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;