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Fix undefined behaviour (left shift of negative value) in long_hash. Also, 

rewrap a line of length > 79, and update comments.
This commit is contained in:
Mark Dickinson 2009-01-26 21:36:30 +00:00
parent 0c2430beda
commit 6ffa4a2a7d
1 changed files with 10 additions and 9 deletions
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19
Objects/longobject.c
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@ -1962,7 +1962,7 @@ long_compare(PyLongObject *a, PyLongObject *b)
static long
long_hash(PyLongObject *v)
{
long x;
unsigned long x;
Py_ssize_t i;
int sign;
@ -1977,17 +1977,18 @@ long_hash(PyLongObject *v)
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
resulting x is nonzero if and only if v is. */
/* The following loop produces a C 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