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Small LZSA2 ratio increase for some files

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Emmanuel Marty 2021-06-04 19:11:22 +02:00 committed by GitHub
parent 65d6972f2c
commit 5e404e93d1
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 78 additions and 2 deletions
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68
src/shrink_block_v2.c
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@ -1310,6 +1310,7 @@ int lzsa_optimize_and_write_block_v2(lzsa_compressor *pCompressor, const unsigne
int* first_offset_for_byte = pCompressor->first_offset_for_byte;
int* next_offset_for_pos = pCompressor->next_offset_for_pos;
int* offset_cache = pCompressor->offset_cache;
int nPosition;
/* Supplement small matches */
@ -1352,12 +1353,77 @@ int lzsa_optimize_and_write_block_v2(lzsa_compressor *pCompressor, const unsigne
match[m].offset = nMatchOffset;
m++;
nInserted++;
if (nInserted >= 15)
if (nInserted >= 12)
break;
}
}
}
/* Supplement matches further */
memset(offset_cache, 0xff, sizeof(int) * 2048);
for (nPosition = nPreviousBlockSize + 1; nPosition < (nEndOffset - 1); nPosition++) {
lzsa_match* match = pCompressor->match + ((nPosition - nPreviousBlockSize) << MATCHES_PER_INDEX_SHIFT_V2);
if (match[0].length < 5) {
int m = 0;
int nMatchPos;
while (m < 46 && match[m].length) {
offset_cache[match[m].offset & 2047] = nPosition;
m++;
}
for (nMatchPos = next_offset_for_pos[nPosition - nPreviousBlockSize]; m < 46 && nMatchPos >= 0; nMatchPos = next_offset_for_pos[nMatchPos - nPreviousBlockSize]) {
int nMatchOffset = nPosition - nMatchPos;
if (nMatchOffset <= MAX_OFFSET) {
int nAlreadyExists = 0;
if (offset_cache[nMatchOffset & 2047] == nPosition) {
int nExistingMatchIdx;
for (nExistingMatchIdx = 0; nExistingMatchIdx < m; nExistingMatchIdx++) {
if (match[nExistingMatchIdx].offset == nMatchOffset) {
nAlreadyExists = 1;
break;
}
}
}
if (!nAlreadyExists) {
int nForwardPos = nPosition + 2;
int nGotMatch = 0;
while (nForwardPos >= nMatchOffset && (nForwardPos + 2) < nEndOffset && nForwardPos < (nPosition + 2 + 1 + 2)) {
if (!memcmp(pInWindow + nForwardPos, pInWindow + nForwardPos - nMatchOffset, 2)) {
nGotMatch = 1;
break;
}
nForwardPos++;
}
if (nGotMatch) {
int nMatchLen = 2;
while (nMatchLen < 16 && nPosition < (nEndOffset - nMatchLen) && pInWindow[nMatchPos + nMatchLen] == pInWindow[nPosition + nMatchLen])
nMatchLen++;
match[m].length = nMatchLen | 0x8000;
match[m].offset = nMatchOffset;
m++;
lzsa_insert_forward_match_v2(pCompressor, pInWindow, nPosition, nMatchOffset, nPreviousBlockSize, nEndOffset, 8);
break;
}
}
}
else {
break;
}
}
}
}
/* Compress optimally with the extra matches */
memset(pCompressor->best_match, 0, BLOCK_SIZE * sizeof(lzsa_match));
lzsa_optimize_forward_v2(pCompressor, pInWindow, pCompressor->best_match - nPreviousBlockSize, nPreviousBlockSize, nPreviousBlockSize + nInDataSize, 1 /* reduce */, 0 /* use forward reps */, nArrivalsPerPosition);

11
src/shrink_context.c
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@ -66,6 +66,7 @@ int lzsa_compressor_init(lzsa_compressor *pCompressor, const int nMaxWindowSize,
pCompressor->rep_len_handled_mask = NULL;
pCompressor->first_offset_for_byte = NULL;
pCompressor->next_offset_for_pos = NULL;
pCompressor->offset_cache = NULL;
pCompressor->min_match_size = nMinMatchSize;
if (pCompressor->min_match_size < nMinMatchSizeForFormat)
pCompressor->min_match_size = nMinMatchSizeForFormat;
@ -116,7 +117,10 @@ int lzsa_compressor_init(lzsa_compressor *pCompressor, const int nMaxWindowSize,
if (pCompressor->first_offset_for_byte) {
pCompressor->next_offset_for_pos = (int*)malloc(BLOCK_SIZE * sizeof(int));
if (pCompressor->next_offset_for_pos) {
return 0;
pCompressor->offset_cache = (int*)malloc(2048 * sizeof(int));
if (pCompressor->offset_cache) {
return 0;
}
}
}
}
@ -146,6 +150,11 @@ int lzsa_compressor_init(lzsa_compressor *pCompressor, const int nMaxWindowSize,
void lzsa_compressor_destroy(lzsa_compressor *pCompressor) {
divsufsort_destroy(&pCompressor->divsufsort_context);
if (pCompressor->offset_cache) {
free(pCompressor->offset_cache);
pCompressor->offset_cache = NULL;
}
if (pCompressor->next_offset_for_pos) {
free(pCompressor->next_offset_for_pos);
pCompressor->next_offset_for_pos = NULL;

1
src/shrink_context.h
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@ -128,6 +128,7 @@ typedef struct _lzsa_compressor {
char *rep_len_handled_mask;
int *first_offset_for_byte;
int *next_offset_for_pos;
int *offset_cache;
int min_match_size;
int format_version;
int flags;