Issue #1772851. Alters long.__hash__ from being *almost* completely
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.
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@ -18,10 +18,21 @@ class HashEqualityTestCase(unittest.TestCase):
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def test_numeric_literals(self):
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self.same_hash(1, 1L, 1.0, 1.0+0.0j)
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self.same_hash(0, 0L, 0.0, 0.0+0.0j)
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self.same_hash(-1, -1L, -1.0, -1.0+0.0j)
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self.same_hash(-2, -2L, -2.0, -2.0+0.0j)
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def test_coerced_integers(self):
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self.same_hash(int(1), long(1), float(1), complex(1),
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int('1'), float('1.0'))
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self.same_hash(int(-2**31), long(-2**31), float(-2**31))
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self.same_hash(int(1-2**31), long(1-2**31), float(1-2**31))
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self.same_hash(int(2**31-1), long(2**31-1), float(2**31-1))
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# for 64-bit platforms
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self.same_hash(int(2**31), long(2**31), float(2**31))
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self.same_hash(int(-2**63), long(-2**63), float(-2**63))
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self.same_hash(int(1-2**63), long(1-2**63))
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self.same_hash(int(2**63-1), long(2**63-1))
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def test_coerced_floats(self):
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self.same_hash(long(1.23e300), float(1.23e300))
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@ -1937,10 +1937,18 @@ long_hash(PyLongObject *v)
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i = -(i);
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}
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#define LONG_BIT_SHIFT (8*sizeof(long) - SHIFT)
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/* The following loop produces a C long x such that (unsigned long)x
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is congruent to the absolute value of v modulo ULONG_MAX. The
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resulting x is nonzero if and only if v is. */
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while (--i >= 0) {
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/* Force a native long #-bits (32 or 64) circular shift */
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x = ((x << SHIFT) & ~MASK) | ((x >> LONG_BIT_SHIFT) & MASK);
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x += v->ob_digit[i];
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/* If the addition above overflowed (thinking of x as
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unsigned), we compensate by incrementing. This preserves
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the value modulo ULONG_MAX. */
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if ((unsigned long)x < v->ob_digit[i])
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x++;
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}
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#undef LONG_BIT_SHIFT
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x = x * sign;
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