Issue #1772851. Optimization of __hash__ to behave better for big big

numbers.
This commit is contained in:
Facundo Batista 2007-09-19 17:53:25 +00:00
parent ae406c6018
commit 8c20244069
2 changed files with 43 additions and 4 deletions

View File

@ -766,10 +766,17 @@ class Decimal(object):
if self._isnan():
raise TypeError('Cannot hash a NaN value.')
return hash(str(self))
i = int(self)
if self == Decimal(i):
return hash(i)
assert self.__nonzero__() # '-0' handled by integer case
if not self:
return 0
if self._isinteger():
op = _WorkRep(self.to_integral_value())
# to make computation feasible for Decimals with large
# exponent, we use the fact that hash(n) == hash(m) for
# any two nonzero integers n and m such that (i) n and m
# have the same sign, and (ii) n is congruent to m modulo
# 2**64-1. So we can replace hash((-1)**s*c*10**e) with
# hash((-1)**s*c*pow(10, e, 2**64-1).
return hash((-1)**op.sign*op.int*pow(10, op.exp, 2**64-1))
return hash(str(self.normalize()))
def as_tuple(self):

View File

@ -910,6 +910,38 @@ class DecimalUsabilityTest(unittest.TestCase):
def test_hash_method(self):
#just that it's hashable
hash(Decimal(23))
test_values = [Decimal(sign*(2**m + n))
for m in [0, 14, 15, 16, 17, 30, 31,
32, 33, 62, 63, 64, 65, 66]
for n in range(-10, 10)
for sign in [-1, 1]]
test_values.extend([
Decimal("-0"), # zeros
Decimal("0.00"),
Decimal("-0.000"),
Decimal("0E10"),
Decimal("-0E12"),
Decimal("10.0"), # negative exponent
Decimal("-23.00000"),
Decimal("1230E100"), # positive exponent
Decimal("-4.5678E50"),
# a value for which hash(n) != hash(n % (2**64-1))
# in Python pre-2.6
Decimal(2**64 + 2**32 - 1),
# selection of values which fail with the old (before
# version 2.6) long.__hash__
Decimal("1.634E100"),
Decimal("90.697E100"),
Decimal("188.83E100"),
Decimal("1652.9E100"),
Decimal("56531E100"),
])
# check that hash(d) == hash(int(d)) for integral values
for value in test_values:
self.assertEqual(hash(value), hash(int(value)))
#the same hash that to an int
self.assertEqual(hash(Decimal(23)), hash(23))
self.assertRaises(TypeError, hash, Decimal('NaN'))