From 67f594f9b5f62c76206332cb96b588a55c5f5ecf Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Wed, 14 Sep 2011 15:10:28 +0200
Subject: [PATCH] Optimize LRANGE to scan the list starting from the head or
 the tail in order to traverse the minimal number of elements. Thanks to
 Didier Spezia for noticing the problem and providing a patch.

---
 src/t_list.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/t_list.c b/src/t_list.c
index 59455d89..5fdaaa8a 100644
--- a/src/t_list.c
+++ b/src/t_list.c
@@ -519,7 +519,12 @@ void lrangeCommand(redisClient *c) {
             p = ziplistNext(o->ptr,p);
         }
     } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
-        listNode *ln = listIndex(o->ptr,start);
+        listNode *ln;
+
+        /* If we are nearest to the end of the list, reach the element
+         * starting from tail and going backward, as it is faster. */
+        if (start > llen/2) start -= llen;
+        ln = listIndex(o->ptr,start);
 
         while(rangelen--) {
             addReplyBulk(c,ln->value);