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Issue #1772851. Alters long.__hash__ from being *almost* completely

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predictable to being completely predictable.  The value of hash(n)
is unchanged for any n that's small enough to be representable as an
int, and also unchanged for the vast majority of long integers n of
reasonable size.
This commit is contained in:
Facundo Batista 2007-09-19 15:10:06 +00:00
parent 673debfd63
commit d544df7ddd
2 changed files with 19 additions and 0 deletions
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8
Objects/longobject.c
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@ -1937,10 +1937,18 @@ long_hash(PyLongObject *v)
i = -(i);
}
#define LONG_BIT_SHIFT (8*sizeof(long) - 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. */
while (--i >= 0) {
/* Force a native long #-bits (32 or 64) circular shift */
x = ((x << SHIFT) & ~MASK) | ((x >> LONG_BIT_SHIFT) & 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])
x++;
}
#undef LONG_BIT_SHIFT
x = x * sign;