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Increase LZSA2 ratio by ~0.02%

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Emmanuel Marty 2019-10-27 14:55:39 +01:00 committed by GitHub
parent 8551c3ff8a
commit 3c4f535e0b
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 56 additions and 29 deletions
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85
src/shrink_block_v2.c
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@ -174,10 +174,64 @@ static inline int lzsa_write_match_varlen_v2(unsigned char *pOutData, int nOutOf
return nOutOffset;
}
/**
* Insert forward rep candidate
*
* @param pCompressor compression context
* @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
* @param i input data window position whose matches are being considered
* @param nMatchOffset match offset to use as rep candidate
* @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
*/
static void lzsa_insert_forward_match_v2(lzsa_compressor *pCompressor, const unsigned char *pInWindow, const int i, const int nMatchOffset, const int nEndOffset, int nDepth) {
lzsa_arrival *arrival = pCompressor->arrival;
int j;
if (nDepth >= 10) return;
for (j = 0; j < NMATCHES_PER_OFFSET && arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].from_slot; j++) {
int nRepOffset = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_offset;
if (nMatchOffset != nRepOffset && nRepOffset && arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_len >= MIN_MATCH_SIZE_V2) {
int nRepPos = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_pos;
int nRepLen = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_len;
if (nRepPos > nMatchOffset &&
(nRepPos - nMatchOffset + nRepLen) <= (nEndOffset - LAST_LITERALS) &&
!memcmp(pInWindow + nRepPos - nRepOffset, pInWindow + nRepPos - nMatchOffset, nRepLen)) {
lzsa_match *fwd_match = pCompressor->match + (nRepPos << 5);
int exists = 0;
int r;
for (r = 0; r < 32 && fwd_match[r].length >= MIN_MATCH_SIZE_V2; r++) {
if (fwd_match[r].offset == nMatchOffset) {
exists = 1;
if (fwd_match[r].length < nRepLen) {
fwd_match[r].length = nRepLen;
lzsa_insert_forward_match_v2(pCompressor, pInWindow, nRepPos, nMatchOffset, nEndOffset, nDepth + 1);
}
break;
}
}
if (!exists && r < 32) {
fwd_match[r].offset = nMatchOffset;
fwd_match[r].length = nRepLen;
lzsa_insert_forward_match_v2(pCompressor, pInWindow, nRepPos, nMatchOffset, nEndOffset, nDepth + 1);
}
}
}
}
}
/**
* Attempt to pick optimal matches using a forward arrivals parser, so as to produce the smallest possible output that decompresses to the same input
*
* @param pCompressor compression context
* @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
* @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
* @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
* @param nInsertForwardReps non-zero to insert forward repmatch candidates, zero to use the previously inserted candidates
@ -289,35 +343,8 @@ static void lzsa_optimize_forward_v2(lzsa_compressor *pCompressor, const unsigne
while (j < NMATCHES_PER_OFFSET)
nMaxRepLen[j++] = 0;
for (j = 0; j < NMATCHES_PER_OFFSET && arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].from_slot; j++) {
int nRepOffset = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_offset;
if (nMatchOffset != nRepOffset && nRepOffset && nInsertForwardReps && arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_len >= MIN_MATCH_SIZE_V2) {
int nRepPos = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_pos;
int nRepLen = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_len;
if (nRepPos > nMatchOffset &&
(nRepPos - nMatchOffset + nRepLen) <= (nEndOffset - LAST_LITERALS) &&
!memcmp(pInWindow + nRepPos - nRepOffset, pInWindow + nRepPos - nMatchOffset, nRepLen)) {
lzsa_match *fwd_match = pCompressor->match + (nRepPos << 5);
int exists = 0;
int r;
for (r = 0; r < 32 && fwd_match[r].length >= MIN_MATCH_SIZE_V2; r++) {
if (fwd_match[r].offset == nMatchOffset) {
exists = 1;
break;
}
}
if (!exists && r < 32) {
fwd_match[r].offset = nMatchOffset;
fwd_match[r].length = nRepLen;
}
}
}
}
if (nInsertForwardReps)
lzsa_insert_forward_match_v2(pCompressor, pInWindow, i, nMatchOffset, nEndOffset, 0);
if (nMatchLen >= LEAVE_ALONE_MATCH_SIZE)
nStartingMatchLen = nMatchLen;