From: Yann Collet <cyan@fb.com>
Date: Tue, 22 May 2018 22:06:36 +0000 (-0700)
Subject: disable 2-passes strategy
X-Git-Tag: v1.3.5~3^2~41^2~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a8ddf1d370fc1ff8e61f75225f756c81ec719c7e;p=thirdparty%2Fzstd.git

disable 2-passes strategy
---

diff --git a/lib/compress/zstd_ldm.c b/lib/compress/zstd_ldm.c
index 03348f177..423aedafd 100644
--- a/lib/compress/zstd_ldm.c
+++ b/lib/compress/zstd_ldm.c
@@ -642,8 +642,6 @@ size_t ZSTD_ldm_blockCompress(rawSeqStore_t* rawSeqStore,
     ZSTD_ldm_limitTableUpdate(ms, ip);
     ZSTD_ldm_fillFastTables(ms, cParams, ip);
     /* Compress the last literals */
-    {   size_t const lastLiterals = blockCompressor(ms, seqStore, rep, cParams,
-                                                    ip, iend - ip);
-        return lastLiterals;
-    }
+    return blockCompressor(ms, seqStore, rep, cParams,
+                           ip, iend - ip);
 }
diff --git a/lib/compress/zstd_opt.c b/lib/compress/zstd_opt.c
index b72eea69e..4295ec1bc 100644
--- a/lib/compress/zstd_opt.c
+++ b/lib/compress/zstd_opt.c
@@ -1012,6 +1012,7 @@ size_t ZSTD_compressBlock_btopt(
 }
 
 
+/* used in 2-pass strategy */
 static U32 ZSTD_upscaleStat(U32* table, U32 lastEltIndex, int bonus)
 {
     U32 s, sum=0;
@@ -1024,7 +1025,8 @@ static U32 ZSTD_upscaleStat(U32* table, U32 lastEltIndex, int bonus)
     return sum;
 }
 
-static void ZSTD_upscaleStats(optState_t* optPtr)
+/* used in 2-pass strategy */
+MEM_STATIC void ZSTD_upscaleStats(optState_t* optPtr)
 {
     optPtr->litSum = ZSTD_upscaleStat(optPtr->litFreq, MaxLit, 0);
     optPtr->litLengthSum = ZSTD_upscaleStat(optPtr->litLengthFreq, MaxLL, 1);
@@ -1037,6 +1039,12 @@ size_t ZSTD_compressBlock_btultra(
         const ZSTD_compressionParameters* cParams, const void* src, size_t srcSize)
 {
     DEBUGLOG(5, "ZSTD_compressBlock_btultra (srcSize=%zu)", srcSize);
+#if 0
+    /* 2-pass strategy (disabled)
+     * this strategy makes a first pass over first block to collect statistics
+     * and seed next round's statistics with it.
+     * The compression ratio gain is generally small (~0.5% on first block),
+     * the cost is 2x cpu time on first block. */
     assert(srcSize <= ZSTD_BLOCKSIZE_MAX);
     if ( (ms->opt.litLengthSum==0)   /* first block */
       && (seqStore->sequences == seqStore->sequencesStart)   /* no ldm */
@@ -1057,6 +1065,7 @@ size_t ZSTD_compressBlock_btultra(
         /* re-inforce weight of collected statistics */
         ZSTD_upscaleStats(&ms->opt);
     }
+#endif
     return ZSTD_compressBlock_opt_generic(ms, seqStore, rep, cParams, src, srcSize, 2 /*optLevel*/, 0 /*extDict*/);
 }