From 553454340be50d8c3d948d191d83e25905472cdb Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <raymond.hettinger@gmail.com>
Date: Wed, 19 Sep 2018 22:58:19 -0700
Subject: [PATCH 1/4] Initially, bound one block at a time

---
 Lib/test/test_deque.py       | 5 +++++
 Modules/_collectionsmodule.c | 6 ++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index 921136069d7722..0f9912cecfb887 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -288,6 +288,11 @@ def test_index(self):
                     else:
                         self.assertEqual(d.index(element, start, stop), target)
 
+        # Test large start argument
+        d = deque(range(0, 10000, 10))
+        i = d.index(9500, 900)
+        self.assertEqual(d[i], 9500)
+
     def test_index_bug_24913(self):
         d = deque('A' * 3)
         with self.assertRaises(ValueError):
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 935b4348a8ff8b..e9a432be2ee632 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -1050,8 +1050,10 @@ deque_index(dequeobject *deque, PyObject *const *args, Py_ssize_t nargs)
         start = stop;
     assert(0 <= start && start <= stop && stop <= Py_SIZE(deque));
 
-    /* XXX Replace this loop with faster code from deque_item() */
-    for (i=0 ; i<start ; i++) {
+    for (i=0 ; i<start-BLOCKLEN ; i+=BLOCKLEN) {
+            b = b->rightlink;
+    }
+    for ( ; i<start ; i++) {
         index++;
         if (index == BLOCKLEN) {
             b = b->rightlink;

From d62453c103eaeea5030f6f7fa06ea55fc9545766 Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <raymond.hettinger@gmail.com>
Date: Wed, 19 Sep 2018 22:59:44 -0700
Subject: [PATCH 2/4] Fix indentation

---
 Modules/_collectionsmodule.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index e9a432be2ee632..ba48076c643fe0 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -1051,7 +1051,7 @@ deque_index(dequeobject *deque, PyObject *const *args, Py_ssize_t nargs)
     assert(0 <= start && start <= stop && stop <= Py_SIZE(deque));
 
     for (i=0 ; i<start-BLOCKLEN ; i+=BLOCKLEN) {
-            b = b->rightlink;
+        b = b->rightlink;
     }
     for ( ; i<start ; i++) {
         index++;

From 6b7e13eadda1c67d77c709978ec7e67c3764a96c Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <raymond.hettinger@gmail.com>
Date: Fri, 21 Sep 2018 00:22:37 -0700
Subject: [PATCH 3/4] Add spaces as requested

---
 Modules/_collectionsmodule.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index ba48076c643fe0..267cf07f1f72a3 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -1050,10 +1050,10 @@ deque_index(dequeobject *deque, PyObject *const *args, Py_ssize_t nargs)
         start = stop;
     assert(0 <= start && start <= stop && stop <= Py_SIZE(deque));
 
-    for (i=0 ; i<start-BLOCKLEN ; i+=BLOCKLEN) {
+    for (i=0 ; i < start - BLOCKLEN ; i += BLOCKLEN) {
         b = b->rightlink;
     }
-    for ( ; i<start ; i++) {
+    for ( ; i < start ; i++) {
         index++;
         if (index == BLOCKLEN) {
             b = b->rightlink;

From f3322aa86be7209a856987bd7172d2dcdc150b44 Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <raymond.hettinger@gmail.com>
Date: Fri, 21 Sep 2018 00:38:16 -0700
Subject: [PATCH 4/4] Expand test to cover different starting offsets

---
 Lib/test/test_deque.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index 0f9912cecfb887..51b66b76aca91d 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -290,8 +290,11 @@ def test_index(self):
 
         # Test large start argument
         d = deque(range(0, 10000, 10))
-        i = d.index(9500, 900)
-        self.assertEqual(d[i], 9500)
+        for step in range(100):
+            i = d.index(8500, 700)
+            self.assertEqual(d[i], 8500)
+            # Repeat test with a different internal offset
+            d.rotate()
 
     def test_index_bug_24913(self):
         d = deque('A' * 3)