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Small LZSA2 token count reduction

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Emmanuel Marty 2019-10-09 13:16:29 +02:00 committed by GitHub
parent 03f841d04f
commit b09dadb1c1
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1 changed files with 20 additions and 0 deletions
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20
src/shrink_block_v2.c
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@ -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;