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bpo-26163: Frozenset hash improvement (GH-5194) (#5198)

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(cherry picked from commit b44c5169f6)
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Miss Islington (bot) 2018-01-16 02:27:15 -08:00 • committed by Raymond Hettinger
parent b92c159efa
commit e7dbd06583
2 changed files with 3 additions and 0 deletions
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Misc/NEWS.d/next/Core and Builtins/2018-01-14-20-32-47.bpo-26163.xv9Iuv.rst Normal file
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@ -0,0 +1,2 @@
Improved frozenset() hash to create more distinct hash values when faced
with datasets containing many similar values.

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Objects/setobject.c
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@ -790,6 +790,7 @@ frozenset_hash(PyObject *self)
hash ^= ((Py_uhash_t)PySet_GET_SIZE(self) + 1) * 1927868237UL; hash ^= ((Py_uhash_t)PySet_GET_SIZE(self) + 1) * 1927868237UL;
/* Disperse patterns arising in nested frozensets */ /* Disperse patterns arising in nested frozensets */
hash ^= (hash >> 11) ^ (~hash >> 25);
hash = hash * 69069U + 907133923UL; hash = hash * 69069U + 907133923UL;
/* -1 is reserved as an error code */ /* -1 is reserved as an error code */