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Add comment and make minor code clean-up to improve clarity.

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Raymond Hettinger 2014-05-18 21:32:40 +01:00
parent 4c5a187c0a
commit 507d997714
1 changed files with 13 additions and 3 deletions
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16
Modules/_collectionsmodule.c
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@ -1831,6 +1831,16 @@ _count_elements(PyObject *self, PyObject *args)
if (mapping_get != NULL && mapping_get == dict_get && if (mapping_get != NULL && mapping_get == dict_get &&
mapping_setitem != NULL && mapping_setitem == dict_setitem) { mapping_setitem != NULL && mapping_setitem == dict_setitem) {
while (1) { while (1) {
/* Fast path advantages:
1. Eliminate double hashing
(by re-using the same hash for both the get and set)
2. Avoid argument overhead of PyObject_CallFunctionObjArgs
(argument tuple creation and parsing)
3. Avoid indirection through a bound method object
(creates another argument tuple)
4. Avoid initial increment from zero
(reuse an existing one-object instead)
*/
Py_hash_t hash; Py_hash_t hash;
key = PyIter_Next(it); key = PyIter_Next(it);
@ -1848,13 +1858,13 @@ _count_elements(PyObject *self, PyObject *args)
oldval = _PyDict_GetItem_KnownHash(mapping, key, hash); oldval = _PyDict_GetItem_KnownHash(mapping, key, hash);
if (oldval == NULL) { if (oldval == NULL) {
if (_PyDict_SetItem_KnownHash(mapping, key, one, hash) == -1) if (_PyDict_SetItem_KnownHash(mapping, key, one, hash) == -1)
break; goto done;
} else { } else {
newval = PyNumber_Add(oldval, one); newval = PyNumber_Add(oldval, one);
if (newval == NULL) if (newval == NULL)
break; goto done;
if (_PyDict_SetItem_KnownHash(mapping, key, newval, hash) == -1) if (_PyDict_SetItem_KnownHash(mapping, key, newval, hash) == -1)
break; goto done;
Py_CLEAR(newval); Py_CLEAR(newval);
} }
Py_DECREF(key); Py_DECREF(key);