From: W. Felix Handte <w@felixhandte.com>
Date: Mon, 17 Aug 2020 21:43:01 +0000 (-0400)
Subject: Fix Off-By-One Error in Counting DDS Search Attempts
X-Git-Tag: v1.4.7~81^2~16
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=df386b3d8d50cef611d7f9693417d63620170bd1;p=thirdparty%2Fzstd.git

Fix Off-By-One Error in Counting DDS Search Attempts

This caused us to double-search the first position and fail to search the
last position in the chain, slowing down search and making it less effective.
---

diff --git a/lib/compress/zstd_lazy.c b/lib/compress/zstd_lazy.c
index 0ee9f6506..5e38e49cc 100644
--- a/lib/compress/zstd_lazy.c
+++ b/lib/compress/zstd_lazy.c
@@ -575,7 +575,7 @@ size_t ZSTD_HcFindBestMatch_generic (
         const U32 ddsMinChain = ddsSize > ddsChainSize ? ddsSize - ddsChainSize : 0;
         const U32 bucketSize           = (1 << DD_BLOG);
 
-        U32 attemptNb = 0;
+        U32 attemptNb = 1;
 
         matchIndex = dms->hashTable[ddsIdx];
 
@@ -603,7 +603,7 @@ size_t ZSTD_HcFindBestMatch_generic (
                 break;
             }
 
-            if (attemptNb < bucketSize - 1) {
+            if (attemptNb < bucketSize) {
                 matchIndex = dms->hashTable[ddsIdx + attemptNb];
             } else {
                 matchIndex = dms->chainTable[matchIndex & ddsChainMask];