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gh-136599: Improve long_hash() (#136600)

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Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
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Pieter Eendebak 2025-09-04 14:27:26 +02:00 • committed by GitHub
parent e46d403d59
commit c9cf019cf5
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2 changed files with 18 additions and 1 deletions
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1
Misc/NEWS.d/next/Core_and_Builtins/2025-07-13-21-21-17.gh-issue-136599.sLhm2O.rst Normal file
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@ -0,0 +1 @@
Improve performance of :class:`int` hash calculations.

18
Objects/longobject.c
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@ -3676,7 +3676,23 @@ long_hash(PyObject *obj)
}
i = _PyLong_DigitCount(v);
sign = _PyLong_NonCompactSign(v);
x = 0;
// unroll first digit
Py_BUILD_ASSERT(PyHASH_BITS > PyLong_SHIFT);
assert(i >= 1);
--i;
x = v->long_value.ob_digit[i];
assert(x < PyHASH_MODULUS);
#if PyHASH_BITS >= 2 * PyLong_SHIFT
// unroll second digit
assert(i >= 1);
--i;
x <<= PyLong_SHIFT;
x += v->long_value.ob_digit[i];
assert(x < PyHASH_MODULUS);
#endif
while (--i >= 0) {
/* Here x is a quantity in the range [0, _PyHASH_MODULUS); we
want to compute x * 2**PyLong_SHIFT + v->long_value.ob_digit[i] modulo