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Move the active entry multiplication to later in the hash calculation

This commit is contained in:
Raymond Hettinger 2015-08-07 00:43:39 -07:00
parent b501a27ad8
commit 4148195c45
1 changed files with 4 additions and 4 deletions
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8
Objects/setobject.c
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@ -760,15 +760,12 @@ static Py_hash_t
frozenset_hash(PyObject *self)
{
PySetObject *so = (PySetObject *)self;
Py_uhash_t hash = 1927868237UL;
Py_uhash_t hash = 0;
setentry *entry;
if (so->hash != -1)
return so->hash;
/* Initial dispersion based on the number of active entries */
hash *= (Py_uhash_t)PySet_GET_SIZE(self) + 1;
/* Xor-in shuffled bits from every entry's hash field because xor is
commutative and a frozenset hash should be independent of order.
@ -790,6 +787,9 @@ frozenset_hash(PyObject *self)
if ((so->fill - so->used) & 1)
hash ^= _shuffle_bits(-1);
/* Factor in the number of active entries */
hash ^= ((Py_uhash_t)PySet_GET_SIZE(self) + 1) * 1927868237UL;
/* Disperse patterns arising in nested frozensets */
hash = hash * 69069U + 907133923UL;