From: W. Felix Handte <w@felixhandte.com>
Date: Thu, 3 Sep 2020 17:58:11 +0000 (-0400)
Subject: Truncate Chain at Last Possible Attempt
X-Git-Tag: v1.4.7~80^2~13
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f42c5bddd9b3b5e2741e93c866b988f97c9f296a;p=thirdparty%2Fzstd.git

Truncate Chain at Last Possible Attempt

Make the chain table denser?
---

diff --git a/lib/compress/zstd_lazy.c b/lib/compress/zstd_lazy.c
index 0b70494fa..edba73d05 100644
--- a/lib/compress/zstd_lazy.c
+++ b/lib/compress/zstd_lazy.c
@@ -487,7 +487,9 @@ void ZSTD_dedicatedDictSearch_lazy_loadDictionary(ZSTD_matchState_t* ms, const B
     U32 const chainMask = chainSize - 1;
     U32 idx = ms->nextToUpdate;
     U32 const minChain = chainSize < target ? target - chainSize : idx;
-    U32 bucketSize = 1 << ZSTD_LAZY_DDSS_BUCKET_LOG;
+    U32 const bucketSize = 1 << ZSTD_LAZY_DDSS_BUCKET_LOG;
+    U32 const nbAttempts = (1 << ms->cParams.searchLog) - bucketSize + 1;
+    U32 const chainLimit = nbAttempts > 255 ? 255 : nbAttempts;
     U32* const chains = (U32*)malloc(chainSize * sizeof(U32));
     assert(chains != NULL);
     assert(idx != 0);
@@ -517,7 +519,7 @@ void ZSTD_dedicatedDictSearch_lazy_loadDictionary(ZSTD_matchState_t* ms, const B
             while (i) {
                 chainTable[chainPos++] = i;
                 count++;
-                if (i < minChain || count >= 255) {
+                if (i < minChain || count >= chainLimit) {
                     break;
                 }
                 i = chains[i & chainMask];