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.
diff --git a/Lib/test/test_hash.py b/Lib/test/test_hash.py
index 3d6c9d1..07b65da 100644
--- a/Lib/test/test_hash.py
+++ b/Lib/test/test_hash.py
@@ -18,10 +18,21 @@
def test_numeric_literals(self):
self.same_hash(1, 1L, 1.0, 1.0+0.0j)
+ self.same_hash(0, 0L, 0.0, 0.0+0.0j)
+ self.same_hash(-1, -1L, -1.0, -1.0+0.0j)
+ self.same_hash(-2, -2L, -2.0, -2.0+0.0j)
def test_coerced_integers(self):
self.same_hash(int(1), long(1), float(1), complex(1),
int('1'), float('1.0'))
+ self.same_hash(int(-2**31), long(-2**31), float(-2**31))
+ self.same_hash(int(1-2**31), long(1-2**31), float(1-2**31))
+ self.same_hash(int(2**31-1), long(2**31-1), float(2**31-1))
+ # for 64-bit platforms
+ self.same_hash(int(2**31), long(2**31), float(2**31))
+ self.same_hash(int(-2**63), long(-2**63), float(-2**63))
+ self.same_hash(int(1-2**63), long(1-2**63))
+ self.same_hash(int(2**63-1), long(2**63-1))
def test_coerced_floats(self):
self.same_hash(long(1.23e300), float(1.23e300))
diff --git a/Objects/longobject.c b/Objects/longobject.c
index abb69b0..f14f298 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -1937,10 +1937,18 @@
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;