From b09dadb1c1bdf15220b72ba6e99f4abf19200199 Mon Sep 17 00:00:00 2001
From: Emmanuel Marty <emmanuel@fgl.com>
Date: Wed, 9 Oct 2019 13:16:29 +0200
Subject: [PATCH] Small LZSA2 token count reduction
---
src/shrink_block_v2.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/src/shrink_block_v2.c b/src/shrink_block_v2.c
index 8214f1e..a86f440 100644
--- a/src/shrink_block_v2.c
+++ b/src/shrink_block_v2.c
@@ -413,7 +413,10 @@ static void lzsa_optimize_forward_v2(lzsa_compressor *pCompressor, const unsigne
static int lzsa_optimize_command_count_v2(lzsa_compressor *pCompressor, const unsigned char *pInWindow, lzsa_match *pBestMatch, const int nStartOffset, const int nEndOffset) {
int i;
int nNumLiterals = 0;
+ int nPrevRepMatchOffset = 0;
int nRepMatchOffset = 0;
+ int nRepMatchLen = 0;
+ int nRepIndex = 0;
int nDidReduce = 0;
for (i = nStartOffset; i < nEndOffset; ) {
@@ -502,6 +505,15 @@ static int lzsa_optimize_command_count_v2(lzsa_compressor *pCompressor, const un
if (pBestMatch[nNextIndex].offset != nRepMatchOffset)
nReducedCommandSize += (pBestMatch[nNextIndex].offset <= 32) ? 4 : ((pBestMatch[nNextIndex].offset <= 512) ? 8 : ((pBestMatch[nNextIndex].offset <= (8192 + 512)) ? 12 : 16));
+ int nReplaceRepOffset = 0;
+ if (nRepMatchOffset && nRepMatchOffset != nPrevRepMatchOffset && nRepMatchLen >= MIN_MATCH_SIZE_V2 && nRepMatchOffset != pBestMatch[nNextIndex].offset && nRepIndex >= pBestMatch[nNextIndex].offset &&
+ (nRepIndex - pBestMatch[nNextIndex].offset + nRepMatchLen) <= (nEndOffset - LAST_LITERALS) &&
+ !memcmp(pInWindow + nRepIndex - nRepMatchOffset, pInWindow + nRepIndex - pBestMatch[nNextIndex].offset, nRepMatchLen)) {
+ /* Replacing this match command by literals would let us create a repmatch */
+ nReplaceRepOffset = 1;
+ nReducedCommandSize -= (nRepMatchOffset <= 32) ? 4 : ((nRepMatchOffset <= 512) ? 8 : ((nRepMatchOffset <= (8192 + 512)) ? 12 : 16));
+ }
+
if (nOriginalCombinedCommandSize >= nReducedCommandSize) {
/* Reduce */
int nMatchLen = pMatch->length;
@@ -512,6 +524,11 @@ static int lzsa_optimize_command_count_v2(lzsa_compressor *pCompressor, const un
}
nDidReduce = 1;
+
+ if (nReplaceRepOffset) {
+ pBestMatch[nRepIndex].offset = pBestMatch[nNextIndex].offset;
+ nRepMatchOffset = pBestMatch[nNextIndex].offset;
+ }
continue;
}
}
@@ -532,7 +549,10 @@ static int lzsa_optimize_command_count_v2(lzsa_compressor *pCompressor, const un
continue;
}
+ nPrevRepMatchOffset = nRepMatchOffset;
nRepMatchOffset = pMatch->offset;
+ nRepMatchLen = pMatch->length;
+ nRepIndex = i;
i += pMatch->length;
nNumLiterals = 0;