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Small improvement of the LZSA2 compression ratio

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Emmanuel Marty 2019-06-21 17:28:17 +02:00 committed by GitHub
parent 1c3911a659
commit 63c261ce2d
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 29 additions and 1 deletions
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2
src/lzsa.c
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@ -46,7 +46,7 @@
#define OPT_RAW 2 #define OPT_RAW 2
#define OPT_FAVOR_RATIO 4 #define OPT_FAVOR_RATIO 4
#define TOOL_VERSION "1.0.0" #define TOOL_VERSION "1.0.1"
/*---------------------------------------------------------------------------*/ /*---------------------------------------------------------------------------*/

28
src/shrink_block_v2.c
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@ -451,6 +451,7 @@ static int lzsa_optimize_command_count_v2(lzsa_compressor *pCompressor, const in
int nNumLiterals = 0; int nNumLiterals = 0;
int nDidReduce = 0; int nDidReduce = 0;
int nPreviousMatchOffset = -1; int nPreviousMatchOffset = -1;
int nRepMatchOffset = 0;
lzsa_repmatch_opt *repmatch_opt = pCompressor->repmatch_opt; lzsa_repmatch_opt *repmatch_opt = pCompressor->repmatch_opt;
for (i = nStartOffset; i < nEndOffset; ) { for (i = nStartOffset; i < nEndOffset; ) {
@ -480,6 +481,19 @@ static int lzsa_optimize_command_count_v2(lzsa_compressor *pCompressor, const in
* match command by literals, the output size will not increase and it will remove one command. */ * match command by literals, the output size will not increase and it will remove one command. */
nReduce = 1; nReduce = 1;
} }
else {
if (nMatchOffset != nRepMatchOffset &&
pCompressor->best_match[i + nMatchLen].offset == nRepMatchOffset) {
int nRepMatchSize = (nRepMatchOffset <= 32) ? 4 : ((nRepMatchOffset <= 512) ? 8 : ((nRepMatchOffset <= (8192 + 512)) ? 12 : 16)) /* match offset */;
if (nCommandSize > ((nMatchLen << 3) + lzsa_get_literals_varlen_size_v2(nNumLiterals + nMatchLen) - nRepMatchSize)) {
/* Same case, replacing this command by literals alone isn't enough on its own to have savings, however this match command is inbetween two matches with
* identical offsets, while this command has a different match offset. Replacing it with literals allows to use a rep-match for the two commands around it, and
* that is enough for some savings. Replace. */
nReduce = 1;
}
}
}
} }
else { else {
int nCurIndex = i + nMatchLen; int nCurIndex = i + nMatchLen;
@ -501,8 +515,22 @@ static int lzsa_optimize_command_count_v2(lzsa_compressor *pCompressor, const in
* more room than the match, and doesn't grow the next match command's literals encoding, go ahead and remove the command. */ * more room than the match, and doesn't grow the next match command's literals encoding, go ahead and remove the command. */
nReduce = 1; nReduce = 1;
} }
else {
if (nCurIndex < nEndOffset && pCompressor->best_match[nCurIndex].length >= MIN_MATCH_SIZE_V2 &&
pCompressor->best_match[nCurIndex].offset != nMatchOffset &&
pCompressor->best_match[nCurIndex].offset == nRepMatchOffset) {
int nRepMatchSize = (nRepMatchOffset <= 32) ? 4 : ((nRepMatchOffset <= 512) ? 8 : ((nRepMatchOffset <= (8192 + 512)) ? 12 : 16)) /* match offset */;
if (nCommandSize > ((nMatchLen << 3) + lzsa_get_literals_varlen_size_v2(nNumLiterals + nNextNumLiterals + nMatchLen) - lzsa_get_literals_varlen_size_v2(nNextNumLiterals) - nRepMatchSize)) {
/* Same case, but now replacing this command allows to use a rep-match and get savings, so do it */
nReduce = 1;
} }
} }
}
}
}
if (pMatch->length)
nRepMatchOffset = pMatch->offset;
if (nReduce) { if (nReduce) {
int j; int j;