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| author | Tim Peters <tim.peters@gmail.com> | 2006-09-05 01:47:53 +0000 |
|---|---|---|
| committer | Tim Peters <tim.peters@gmail.com> | 2006-09-05 01:47:53 +0000 |
| commit | cbdd350dd7e393933437d5c12eabe8e47b6a40d9 (patch) | |
| tree | 2762ddd912dcd47079d896b0d262fcfcb4675d94 | |
| parent | 3467352fe21270db6ed09d2d0213d02cc8c1e9e5 (diff) | |
| download | cpython-git-cbdd350dd7e393933437d5c12eabe8e47b6a40d9.tar.gz | |
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.
| -rw-r--r-- | Misc/NEWS | 7 | ||||
| -rw-r--r-- | Objects/intobject.c | 10 |
2 files changed, 13 insertions, 4 deletions
@@ -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. diff --git a/Objects/intobject.c b/Objects/intobject.c index c7137df40b..b94e3e9887 100644 --- a/Objects/intobject.c +++ b/Objects/intobject.c @@ -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; |