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bpo-8425: Set inplace difference fash path for large complement sets #15590

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Merged
rhettinger merged 1 commit into from
Aug 29, 2019
Merged

bpo-8425: Set inplace difference fash path for large complement sets #15590

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-08-29-01-55-38.bpo-8425.FTq4A8.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Optimize set difference_update for the case when the other set is much
larger than the base set. (Suggested by Evgeny Kapun with code contributed
by Michele Orrù).
18 changes: 17 additions & 1 deletion Objects/setobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1463,9 +1463,25 @@ set_difference_update_internal(PySetObject *so, PyObject *other)
setentry *entry;
Py_ssize_t pos = 0;

/* Optimization: When the other set is more than 8 times
larger than the base set, replace the other set with
interesection of the two sets.
*/
if ((PySet_GET_SIZE(other) >> 3) > PySet_GET_SIZE(so)) {
other = set_intersection(so, other);
if (other == NULL)
return -1;
} else {
Py_INCREF(other);
}

while (set_next((PySetObject *)other, &pos, &entry))
if (set_discard_entry(so, entry->key, entry->hash) < 0)
if (set_discard_entry(so, entry->key, entry->hash) < 0) {
Py_DECREF(other);
return -1;
}

Py_DECREF(other);
} else {
PyObject *key, *it;
it = PyObject_GetIter(other);
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