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gh-94603: micro optimize list.pop (gh-94604)

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Pieter Eendebak 2022-12-27 11:55:54 +01:00 committed by GitHub
parent ce39aaffee
commit b3da698952
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2 changed files with 21 additions and 12 deletions
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1
Misc/NEWS.d/next/Core and Builtins/2022-07-06-18-44-00.gh-issue-94603.Q_03xV.rst Normal file
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@ -0,0 +1 @@
Improve performance of ``list.pop`` for small lists.

32
Objects/listobject.c
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@ -1022,21 +1022,29 @@ list_pop_impl(PyListObject *self, Py_ssize_t index)
PyErr_SetString(PyExc_IndexError, "pop index out of range");
return NULL;
}
v = self->ob_item[index];
if (index == Py_SIZE(self) - 1) {
status = list_resize(self, Py_SIZE(self) - 1);
if (status >= 0)
return v; /* and v now owns the reference the list had */
else
return NULL;
PyObject **items = self->ob_item;
v = items[index];
const Py_ssize_t size_after_pop = Py_SIZE(self) - 1;
if (size_after_pop == 0) {
Py_INCREF(v);
status = _list_clear(self);
}
Py_INCREF(v);
status = list_ass_slice(self, index, index+1, (PyObject *)NULL);
if (status < 0) {
Py_DECREF(v);
else {
if ((size_after_pop - index) > 0) {
memmove(&items[index], &items[index+1], (size_after_pop - index) * sizeof(PyObject *));
}
status = list_resize(self, size_after_pop);
}
if (status >= 0) {
return v; // and v now owns the reference the list had
}
else {
// list resize failed, need to restore
memmove(&items[index+1], &items[index], (size_after_pop - index)* sizeof(PyObject *));
items[index] = v;
return NULL;
}
return v;
}
/* Reverse a slice of a list in place, from lo up to (exclusive) hi. */