Mercurial > cpython-lru_cache-weakref
diff Objects/longobject.c @ 51076:ca8ea52b45c3 2.6
Merged revisions 68974-68975 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
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r68974 | mark.dickinson | 2009-01-26 21:36:30 +0000 (Mon, 26 Jan 2009) | 4 lines
Fix undefined behaviour (left shift of negative value) in long_hash. Also,
rewrap a line of length > 79, and update comments.
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r68975 | mark.dickinson | 2009-01-26 21:40:08 +0000 (Mon, 26 Jan 2009) | 2 lines
Fix comment.
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| author | Mark Dickinson <dickinsm@gmail.com> |
|---|---|
| date | Mon, 26 Jan 2009 21:43:42 +0000 |
| parents | 096b488438e9 |
| children | c5b7958f4292 |
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--- a/Objects/longobject.c Mon Jan 26 17:20:15 2009 +0000 +++ b/Objects/longobject.c Mon Jan 26 21:43:42 2009 +0000 @@ -1962,7 +1962,7 @@ static long long_hash(PyLongObject *v) { - long x; + unsigned long x; Py_ssize_t i; int sign; @@ -1977,17 +1977,18 @@ i = -(i); } #define LONG_BIT_PyLong_SHIFT (8*sizeof(long) - PyLong_SHIFT) - /* The following loop produces a C long x such that (unsigned long)x - is congruent to the absolute value of v modulo ULONG_MAX. The + /* The following loop produces a C unsigned long x such that x is + congruent to the absolute value of v modulo ULONG_MAX. The resulting x is nonzero if and only if v is. */ while (--i >= 0) { /* Force a native long #-bits (32 or 64) circular shift */ - x = ((x << PyLong_SHIFT) & ~PyLong_MASK) | ((x >> LONG_BIT_PyLong_SHIFT) & PyLong_MASK); + x = ((x << PyLong_SHIFT) & ~PyLong_MASK) | + ((x >> LONG_BIT_PyLong_SHIFT) & PyLong_MASK); x += v->ob_digit[i]; - /* If the addition above overflowed (thinking of x as - unsigned), we compensate by incrementing. This preserves - the value modulo ULONG_MAX. */ - if ((unsigned long)x < v->ob_digit[i]) + /* If the addition above overflowed we compensate by + incrementing. This preserves the value modulo + ULONG_MAX. */ + if (x < v->ob_digit[i]) x++; } #undef LONG_BIT_PyLong_SHIFT