1 files changed, 29 insertions, 2 deletions

diff --git a/src/t_zset.c b/src/t_zset.c
index 4b28c24ef..2ef02ac8a 100644
--- a/src/t_zset.c
+++ b/src/t_zset.c
@@ -1283,6 +1283,10 @@ int zsetScore(robj *zobj, sds member, double *score) {
  *            assume 0 as previous score.
  * ZADD_NX:   Perform the operation only if the element does not exist.
  * ZADD_XX:   Perform the operation only if the element already exist.
+ * ZADD_GT:   Perform the operation on existing elements only if the new score is 
+ *            greater than the current score.
+ * ZADD_LT:   Perform the operation on existing elements only if the new score is 
+ *            less than the current score.
  *
  * When ZADD_INCR is used, the new score of the element is stored in
  * '*newscore' if 'newscore' is not NULL.
@@ -1317,6 +1321,8 @@ int zsetAdd(robj *zobj, double score, sds ele, int *flags, double *newscore) {
     int incr = (*flags & ZADD_INCR) != 0;
     int nx = (*flags & ZADD_NX) != 0;
     int xx = (*flags & ZADD_XX) != 0;
+    int gt = (*flags & ZADD_GT) != 0;
+    int lt = (*flags & ZADD_LT) != 0;
     *flags = 0; /* We'll return our response flags. */
     double curscore;
 
@@ -1348,7 +1354,12 @@ int zsetAdd(robj *zobj, double score, sds ele, int *flags, double *newscore) {
             }
 
             /* Remove and re-insert when score changed. */
-            if (score != curscore) {
+            if (score != curscore &&  
+                /* LT? Only update if score is less than current. */
+                (!lt || score < curscore) &&
+                /* GT? Only update if score is greater than current. */
+                (!gt || score > curscore)) 
+            {
                 zobj->ptr = zzlDelete(zobj->ptr,eptr);
                 zobj->ptr = zzlInsert(zobj->ptr,ele,score);
                 *flags |= ZADD_UPDATED;
@@ -1393,7 +1404,12 @@ int zsetAdd(robj *zobj, double score, sds ele, int *flags, double *newscore) {
             }
 
             /* Remove and re-insert when score changes. */
-            if (score != curscore) {
+            if (score != curscore &&  
+                /* LT? Only update if score is less than current. */
+                (!lt || score < curscore) &&
+                /* GT? Only update if score is greater than current. */
+                (!gt || score > curscore)) 
+            {
                 znode = zslUpdateScore(zs->zsl,curscore,ele,score);
                 /* Note that we did not removed the original element from
                  * the hash table representing the sorted set, so we just
@@ -1555,6 +1571,8 @@ void zaddGenericCommand(client *c, int flags) {
         else if (!strcasecmp(opt,"xx")) flags |= ZADD_XX;
         else if (!strcasecmp(opt,"ch")) flags |= ZADD_CH;
         else if (!strcasecmp(opt,"incr")) flags |= ZADD_INCR;
+        else if (!strcasecmp(opt,"gt")) flags |= ZADD_GT;
+        else if (!strcasecmp(opt,"lt")) flags |= ZADD_LT;
         else break;
         scoreidx++;
     }
@@ -1564,6 +1582,8 @@ void zaddGenericCommand(client *c, int flags) {
     int nx = (flags & ZADD_NX) != 0;
     int xx = (flags & ZADD_XX) != 0;
     int ch = (flags & ZADD_CH) != 0;
+    int gt = (flags & ZADD_GT) != 0;
+    int lt = (flags & ZADD_LT) != 0;
 
     /* After the options, we expect to have an even number of args, since
      * we expect any number of score-element pairs. */
@@ -1580,6 +1600,13 @@ void zaddGenericCommand(client *c, int flags) {
             "XX and NX options at the same time are not compatible");
         return;
     }
+    
+    if ((gt && nx) || (lt && nx) || (gt && lt)) {
+        addReplyError(c,
+            "GT, LT, and/or NX options at the same time are not compatible");
+        return;
+    }
+    /* Note that XX is compatible with either GT or LT */
 
     if (incr && elements > 1) {
         addReplyError(c,