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gh-136599: Improve long_hash #136600

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gh-136599: Improve long_hash #136600

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146f5aa
Add test for long_hash
eendebakpt Jul 12, 2025
a162da2
Unroll first digit calculation in long_hash
eendebakpt Jul 12, 2025
4f9fc76
Unroll second digit calculation in long_hash
eendebakpt Jul 12, 2025
07bce4b
whitespace
eendebakpt Jul 12, 2025
32341de
add gh number
eendebakpt Jul 12, 2025
194fb7a
Merge branch 'long_hash' of github.com:eendebakpt/cpython into long_hash
eendebakpt Jul 12, 2025
a48860f
review comments
eendebakpt Jul 13, 2025
6d3754b
fix test on wasi
eendebakpt Jul 13, 2025
fec9fbe
add news entry
eendebakpt Jul 13, 2025
08d7ba9
review comments
eendebakpt Jul 25, 2025
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@eendebakpt
eendebakpt committed Jul 25, 2025
commit 08d7ba93e78d88ec3b8edab77ef2553c26b4417e
14 changes: 11 additions & 3 deletions Lib/test/test_long.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1696,10 +1696,18 @@ class MyInt(int):
def test_hash(self):
# gh-136599
self.assertEqual(hash(-1), -2)
self.assertEqual(hash(0), 0)
self.assertEqual(hash(10), 10)
self.assertEqual(hash(2**31 - 2), 2**31 - 2)
self.assertNotEqual(hash(-2**31), -1)
self.assertNotEqual(hash(-2**61), -1)

self.assertEqual(hash(sys.hash_info.modulus - 2), sys.hash_info.modulus - 2)
self.assertEqual(hash(sys.hash_info.modulus - 1), sys.hash_info.modulus - 1)
self.assertEqual(hash(sys.hash_info.modulus), 0)
self.assertEqual(hash(sys.hash_info.modulus + 1), 1)

self.assertEqual(hash(-sys.hash_info.modulus - 2), -2)
self.assertEqual(hash(-sys.hash_info.modulus - 1), -2)
self.assertEqual(hash(-sys.hash_info.modulus), 0)
self.assertEqual(hash(-sys.hash_info.modulus + 1), - (sys.hash_info.modulus - 1))


if __name__ == "__main__":
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4 changes: 3 additions & 1 deletion Objects/longobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3678,11 +3678,13 @@ long_hash(PyObject *obj)
sign = _PyLong_NonCompactSign(v);

// unroll first two digits
#if ( PyHASH_BITS > PyLong_SHIFT )
assert(i>=2);
--i;
x = v->long_value.ob_digit[i];
assert(x < _PyHASH_MODULUS);
#if ( PyHASH_BITS > (2*PyLong_SHIFT))
#endif
#if ( PyHASH_BITS > (2 * PyLong_SHIFT) )
--i;
x = ((x << PyLong_SHIFT));
x += v->long_value.ob_digit[i];
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