bpo-26163: Frozenset hash improvement (#5194)

b44c5169 · Raymond Hettinger · GitHub · 94e1696d · b44c5169 · b44c5169
Unverified Kaydet (Commit) b44c5169 authored Ock 16, 2018 tarafından Raymond Hettinger Kaydeden (comit) GitHub Ock 16, 2018
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2018-01-14-20-32-47.bpo-26163.xv9Iuv.rst ...ore and Builtins/2018-01-14-20-32-47.bpo-26163.xv9Iuv.rst +2 -0

setobject.c Objects/setobject.c +1 -0

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--- a/Misc/NEWS.d/next/Core and Builtins/2018-01-14-20-32-47.bpo-26163.xv9Iuv.rst
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-01-14-20-32-47.bpo-26163.xv9Iuv.rst
+Improved frozenset() hash to create more distinct hash values when faced
+with datasets containing many similar values.
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -795,6 +795,7 @@ frozenset_hash(PyObject *self)
    hash ^= ((Py_uhash_t)PySet_GET_SIZE(self) + 1) * 1927868237UL;

    /* Disperse patterns arising in nested frozensets */
+    hash ^= (hash >> 11) ^ (~hash >> 25);
    hash = hash * 69069U + 907133923UL;

    /* -1 is reserved as an error code */