gh-116477: Improve performance of range() when start is 0 and step is 1 (#116478)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>
Co-authored-by: Stan Ulbrych <stan@python.org>

Author: 4 people

Misc/NEWS.d/next/Core_and_Builtins/2024-03-07-22-38-07.gh-issue-116477.AqwRAV.rst

@@ -0,0 +1 @@
+Speed up the :class:`range` object constructor in the case of a single argument.

Objects/rangeobject.c

@@ -259,6 +259,14 @@ compute_range_length(PyObject *start, PyObject *stop, PyObject *step)
     assert(PyLong_Check(stop));
     assert(PyLong_Check(step));
 
+    /* fast path for start == 0 and step == 1: length is max(stop, 0) */
+    if (start == zero && step == one) {
+        if (_PyLong_IsPositive((const PyLongObject *)stop)) {
+            return Py_NewRef(stop);
+        }
+        return zero;
+    }
+
     /* fast path when all arguments fit into a long integer */
     long len = compute_range_length_long(start, stop, step);
     if (len >= 0) {