Issue python#6334: Fix buggy internal length calculation in builtin range function

Author: mdickinson

Lib/test/test_builtin.py

@@ -924,6 +924,24 @@ def test_range(self):
         self.assertEqual(list(range(1, 10, 3)), [1, 4, 7])
         #self.assertEqual(list(range(5, -5, -3)), [5, 2, -1, -4])
 
+        #issue 6334: the internal stored range length was being
+        #computed incorrectly in some cases involving large arguments.
+        x = range(10**20, 10**20+10, 3)
+        self.assertEqual(len(x), 4)
+        self.assertEqual(len(list(x)), 4)
+
+        x = range(10**20+10, 10**20, 3)
+        self.assertEqual(len(x), 0)
+        self.assertEqual(len(list(x)), 0)
+
+        x = range(10**20, 10**20+10, -3)
+        self.assertEqual(len(x), 0)
+        self.assertEqual(len(list(x)), 0)
+
+        x = range(10**20+10, 10**20, -3)
+        self.assertEqual(len(x), 4)
+        self.assertEqual(len(list(x)), 4)
+
         """ XXX(nnorwitz):
         # Now test range() with longs
         self.assertEqual(list(range(-2**100)), [])

Objects/rangeobject.c

@@ -581,7 +581,6 @@ range_iter(PyObject *seq)
 {
     rangeobject *r = (rangeobject *)seq;
     longrangeiterobject *it;
-    PyObject *tmp, *len;
     long lstart, lstop, lstep;
 
     assert(PyRange_Check(seq));
@@ -612,15 +611,9 @@ range_iter(PyObject *seq)
 
     it->len = it->index = NULL;
 
-    /* Calculate length: (r->stop - r->start) / r->step */
-    tmp = PyNumber_Subtract(r->stop, r->start);
-    if (!tmp)
+    it->len = range_length_obj(r);
+    if (!it->len)
         goto create_failure;
-    len = PyNumber_FloorDivide(tmp, r->step);
-    Py_DECREF(tmp);
-    if (!len)
-        goto create_failure;
-    it->len = len;
     it->index = PyLong_FromLong(0);
     if (!it->index)
         goto create_failure;