bpo-41902: Micro optimization for compute_item of range (GH-22492)
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-10-02-13-32-05.bpo-41902.ZKTxzW.rst b/Misc/NEWS.d/next/Core and Builtins/2020-10-02-13-32-05.bpo-41902.ZKTxzW.rst
new file mode 100644
index 0000000..b118a6a
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-10-02-13-32-05.bpo-41902.ZKTxzW.rst
@@ -0,0 +1,3 @@
+Micro optimization when compute :c:member:`~PySequenceMethods.sq_item` and
+:c:member:`~PyMappingMethods.mp_subscript` of :class:`range`. Patch by
+Dong-hee Na.
diff --git a/Objects/rangeobject.c b/Objects/rangeobject.c
index ba6d425..eaa48d5 100644
--- a/Objects/rangeobject.c
+++ b/Objects/rangeobject.c
@@ -254,11 +254,17 @@ compute_item(rangeobject *r, PyObject *i)
/* PyLong equivalent to:
* return r->start + (i * r->step)
*/
- incr = PyNumber_Multiply(i, r->step);
- if (!incr)
- return NULL;
- result = PyNumber_Add(r->start, incr);
- Py_DECREF(incr);
+ if (r->step == _PyLong_One) {
+ result = PyNumber_Add(r->start, i);
+ }
+ else {
+ incr = PyNumber_Multiply(i, r->step);
+ if (!incr) {
+ return NULL;
+ }
+ result = PyNumber_Add(r->start, incr);
+ Py_DECREF(incr);
+ }
return result;
}