From 4793ae3b8429dbd1d59410a62df0dff0990f6861 Mon Sep 17 00:00:00 2001
From: senhuang42 <senhuang96@fb.com>
Date: Wed, 30 Sep 2020 12:54:45 -0400
Subject: [PATCH] Prevent duplicate LDMs from being inserted

---
 lib/compress/zstd_opt.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/compress/zstd_opt.c b/lib/compress/zstd_opt.c
index d6c728462..088282ca2 100644
--- a/lib/compress/zstd_opt.c
+++ b/lib/compress/zstd_opt.c
@@ -868,6 +868,10 @@ static void ldm_maybeAddLdm(ZSTD_match_t* matches, U32* nbMatches,
          * the ldm match down as necessary.
          */
         if (candidateMatchLength == matches[*nbMatches-1].len) {
+            if (candidateOffCode == matches[*nbMatches-1].off) {
+                /* No need to insert the match if it's the exact same */
+                return;
+            }
             U32 candidateMatchIdx = *nbMatches;
             matches[*nbMatches].len = candidateMatchLength;
             matches[*nbMatches].off = candidateOffCode;