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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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This commit is contained in:
Mark Dickinson 2009-01-26 21:43:42 +00:00
parent f66326f8bd
commit 24058549f5
1 changed files with 9 additions and 8 deletions
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17
Objects/longobject.c
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@ -1962,7 +1962,7 @@ long_compare(PyLongObject *a, PyLongObject *b)
static long static long
long_hash(PyLongObject *v) long_hash(PyLongObject *v)
{ {
long x; unsigned long x;
Py_ssize_t i; Py_ssize_t i;
int sign; int sign;
@ -1977,17 +1977,18 @@ long_hash(PyLongObject *v)
i = -(i); i = -(i);
} }
#define LONG_BIT_PyLong_SHIFT (8*sizeof(long) - PyLong_SHIFT) #define LONG_BIT_PyLong_SHIFT (8*sizeof(long) - PyLong_SHIFT)
/* The following loop produces a C long x such that (unsigned long)x /* The following loop produces a C unsigned long x such that x is
is congruent to the absolute value of v modulo ULONG_MAX. The congruent to the absolute value of v modulo ULONG_MAX. The
resulting x is nonzero if and only if v is. */ resulting x is nonzero if and only if v is. */
while (--i >= 0) { while (--i >= 0) {
/* Force a native long #-bits (32 or 64) circular shift */ /* 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]; x += v->ob_digit[i];
/* If the addition above overflowed (thinking of x as /* If the addition above overflowed we compensate by
unsigned), we compensate by incrementing. This preserves incrementing. This preserves the value modulo
the value modulo ULONG_MAX. */ ULONG_MAX. */
if ((unsigned long)x < v->ob_digit[i]) if (x < v->ob_digit[i])
x++; x++;
} }
#undef LONG_BIT_PyLong_SHIFT #undef LONG_BIT_PyLong_SHIFT