Special case endpoint access for speed.

Modules/collectionsmodule.c

@@ -326,6 +326,13 @@ deque_item(dequeobject *deque, int i)
 		return NULL;
 	}
 
+	if (i == 0) {
+		i = deque->leftindex;
+		b = deque->leftblock;
+	} else if (i == deque->len - 1) {
+		i = deque->rightindex;
+		b = deque->rightblock;
+	} else {
 		i += deque->leftindex;
 		n = i / BLOCKLEN;
 		i %= BLOCKLEN;
@@ -339,6 +346,7 @@ deque_item(dequeobject *deque, int i)
 			while (n--)
 				b = b->leftlink;
 		}
+	}
 	item = b->data[i];
 	Py_INCREF(item);
 	return item;