From 7cfeb8cccf945e5de7210d8bd5a398acfd0959d8 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 0690fd2f..71436198 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);