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lzsa/src/shrink.c

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/*
* shrink.c - block compressor implementation
*
* The following copying information applies to this specific source code file:
*
* Written in 2019 by Emmanuel Marty <marty.emmanuel@gmail.com>
* With help, ideas, optimizations and speed measurements by spke <zxintrospec@gmail.com>
* Portions written in 2014-2015 by Eric Biggers <ebiggers3@gmail.com>
*
* To the extent possible under law, the author(s) have dedicated all copyright
* and related and neighboring rights to this software to the public domain
* worldwide via the Creative Commons Zero 1.0 Universal Public Domain
* Dedication (the "CC0").
*
* This software is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the CC0 for more details.
*
* You should have received a copy of the CC0 along with this software; if not
* see <http://creativecommons.org/publicdomain/zero/1.0/>.
*/
/*
* Uses the libdivsufsort library Copyright (c) 2003-2008 Yuta Mori
*
* Inspired by LZ4 by Yann Collet. https://github.com/lz4/lz4
* With ideas from Lizard by Przemyslaw Skibinski and Yann Collet. https://github.com/inikep/lizard
* Also with ideas from smallz4 by Stephan Brumme. https://create.stephan-brumme.com/smallz4/
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "shrink.h"
#include "format.h"
#define LCP_BITS 15
#define LCP_MAX (1<<(LCP_BITS - 1))
#define LCP_SHIFT (32-LCP_BITS)
#define LCP_MASK (((1<<LCP_BITS) - 1) << LCP_SHIFT)
#define POS_MASK ((1<<LCP_SHIFT) - 1)
#define NMATCHES_PER_OFFSET 8
#define MATCHES_PER_OFFSET_SHIFT 3
#define LEAVE_ALONE_MATCH_SIZE 1000
#define LAST_MATCH_OFFSET 4
#define LAST_LITERALS 1
#define MODESWITCH_PENALTY 1
/** One match */
typedef struct _lzsa_match {
unsigned short length;
unsigned short offset;
} lzsa_match;
/**
* Initialize compression context
*
* @param pCompressor compression context to initialize
* @param nMaxWindowSize maximum size of input data window (previously compressed bytes + bytes to compress)
* @param nMinMatchSize minimum match size (cannot be less than MIN_MATCH_SIZE)
* @param nFlags compression flags
*
* @return 0 for success, non-zero for failure
*/
int lzsa_compressor_init(lsza_compressor *pCompressor, const int nMaxWindowSize, const int nMinMatchSize, const int nFlags) {
int nResult;
nResult = divsufsort_init(&pCompressor->divsufsort_context);
pCompressor->intervals = NULL;
pCompressor->pos_data = NULL;
pCompressor->open_intervals = NULL;
pCompressor->match = NULL;
pCompressor->min_match_size = nMinMatchSize;
if (pCompressor->min_match_size < MIN_MATCH_SIZE)
pCompressor->min_match_size = MIN_MATCH_SIZE;
else if (pCompressor->min_match_size > (MATCH_RUN_LEN - 1))
pCompressor->min_match_size = MATCH_RUN_LEN - 1;
pCompressor->flags = nFlags;
pCompressor->num_commands = 0;
if (!nResult) {
pCompressor->intervals = (unsigned int *)malloc(nMaxWindowSize * sizeof(unsigned int));
if (pCompressor->intervals) {
pCompressor->pos_data = (unsigned int *)malloc(nMaxWindowSize * sizeof(unsigned int));
if (pCompressor->pos_data) {
pCompressor->open_intervals = (unsigned int *)malloc((LCP_MAX + 1) * sizeof(unsigned int));
if (pCompressor->open_intervals) {
pCompressor->match = (lzsa_match *)malloc(nMaxWindowSize * NMATCHES_PER_OFFSET * sizeof(lzsa_match));
if (pCompressor->match)
return 0;
}
}
}
}
lzsa_compressor_destroy(pCompressor);
return 100;
}
/**
* Clean up compression context and free up any associated resources
*
* @param pCompressor compression context to clean up
*/
void lzsa_compressor_destroy(lsza_compressor *pCompressor) {
divsufsort_destroy(&pCompressor->divsufsort_context);
if (pCompressor->match) {
free(pCompressor->match);
pCompressor->match = NULL;
}
if (pCompressor->open_intervals) {
free(pCompressor->open_intervals);
pCompressor->open_intervals = NULL;
}
if (pCompressor->pos_data) {
free(pCompressor->pos_data);
pCompressor->pos_data = NULL;
}
if (pCompressor->intervals) {
free(pCompressor->intervals);
pCompressor->intervals = NULL;
}
}
/**
* Parse input data, build suffix array and overlaid data structures to speed up match finding
*
* @param pCompressor compression context
* @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
* @param nInWindowSize total input size in bytes (previously compressed bytes + bytes to compress)
*
* @return 0 for success, non-zero for failure
*/
static int lzsa_build_suffix_array(lsza_compressor *pCompressor, const unsigned char *pInWindow, const int nInWindowSize) {
unsigned int *intervals = pCompressor->intervals;
/* Build suffix array from input data */
if (divsufsort_build_array(&pCompressor->divsufsort_context, pInWindow, (saidx_t*)intervals, nInWindowSize) != 0) {
return 100;
}
int *PLCP = (int*)pCompressor->pos_data; /* Use temporarily */
int *Phi = PLCP;
int nCurLen = 0;
int i;
/* Compute the permuted LCP first (K<>rkk<6B>inen method) */
Phi[intervals[0]] = -1;
for (i = 1; i < nInWindowSize; i++)
Phi[intervals[i]] = intervals[i - 1];
for (i = 0; i < nInWindowSize; i++) {
if (Phi[i] == -1) {
PLCP[i] = 0;
continue;
}
int nMaxLen = (i > Phi[i]) ? (nInWindowSize - i) : (nInWindowSize - Phi[i]);
while (nCurLen < nMaxLen && pInWindow[i + nCurLen] == pInWindow[Phi[i] + nCurLen]) nCurLen++;
PLCP[i] = nCurLen;
if (nCurLen > 0)
nCurLen--;
}
/* Rotate permuted LCP into the LCP. This has better cache locality than the direct Kasai LCP method. This also
* saves us from having to build the inverse suffix array index, as the LCP is calculated without it using this method,
* and the interval builder below doesn't need it either. */
intervals[0] &= POS_MASK;
int nMinMatchSize = pCompressor->min_match_size;
for (i = 1; i < nInWindowSize - 1; i++) {
int nIndex = (int)(intervals[i] & POS_MASK);
int nLen = PLCP[nIndex];
if (nLen < nMinMatchSize)
nLen = 0;
if (nLen > LCP_MAX)
nLen = LCP_MAX;
intervals[i] = ((unsigned int)nIndex) | (((unsigned int)nLen) << LCP_SHIFT);
}
if (i < nInWindowSize)
intervals[i] &= POS_MASK;
/**
* Build intervals for finding matches
*
* Methodology and code fragment taken from wimlib (CC0 license):
* https://wimlib.net/git/?p=wimlib;a=blob_plain;f=src/lcpit_matchfinder.c;h=a2d6a1e0cd95200d1f3a5464d8359d5736b14cbe;hb=HEAD
*/
unsigned int * const SA_and_LCP = intervals;
unsigned int *pos_data = pCompressor->pos_data;
unsigned int next_interval_idx;
unsigned int *top = pCompressor->open_intervals;
unsigned int prev_pos = SA_and_LCP[0] & POS_MASK;
*top = 0;
intervals[0] = 0;
next_interval_idx = 1;
for (int r = 1; r < nInWindowSize; r++) {
const unsigned int next_pos = SA_and_LCP[r] & POS_MASK;
const unsigned int next_lcp = SA_and_LCP[r] & LCP_MASK;
const unsigned int top_lcp = *top & LCP_MASK;
if (next_lcp == top_lcp) {
/* Continuing the deepest open interval */
pos_data[prev_pos] = *top;
}
else if (next_lcp > top_lcp) {
/* Opening a new interval */
*++top = next_lcp | next_interval_idx++;
pos_data[prev_pos] = *top;
}
else {
/* Closing the deepest open interval */
pos_data[prev_pos] = *top;
for (;;) {
const unsigned int closed_interval_idx = *top-- & POS_MASK;
const unsigned int superinterval_lcp = *top & LCP_MASK;
if (next_lcp == superinterval_lcp) {
/* Continuing the superinterval */
intervals[closed_interval_idx] = *top;
break;
}
else if (next_lcp > superinterval_lcp) {
/* Creating a new interval that is a
* superinterval of the one being
* closed, but still a subinterval of
* its superinterval */
*++top = next_lcp | next_interval_idx++;
intervals[closed_interval_idx] = *top;
break;
}
else {
/* Also closing the superinterval */
intervals[closed_interval_idx] = *top;
}
}
}
prev_pos = next_pos;
}
/* Close any still-open intervals. */
pos_data[prev_pos] = *top;
for (; top > pCompressor->open_intervals; top--)
intervals[*top & POS_MASK] = *(top - 1);
/* Success */
return 0;
}
/**
* Find matches at the specified offset in the input window
*
* @param pCompressor compression context
* @param nOffset offset to find matches at, in the input window
* @param pMatches pointer to returned matches
* @param nMaxMatches maximum number of matches to return (0 for none)
*
* @return number of matches
*/
static int lzsa_find_matches_at(lsza_compressor *pCompressor, const int nOffset, lzsa_match *pMatches, const int nMaxMatches) {
unsigned int *intervals = pCompressor->intervals;
unsigned int *pos_data = pCompressor->pos_data;
unsigned int ref;
unsigned int super_ref;
unsigned int match_pos;
lzsa_match *matchptr;
/**
* Find matches using intervals
*
* Taken from wimlib (CC0 license):
* https://wimlib.net/git/?p=wimlib;a=blob_plain;f=src/lcpit_matchfinder.c;h=a2d6a1e0cd95200d1f3a5464d8359d5736b14cbe;hb=HEAD
*/
/* Get the deepest lcp-interval containing the current suffix. */
ref = pos_data[nOffset];
pos_data[nOffset] = 0;
/* Ascend until we reach a visited interval, the root, or a child of the
* root. Link unvisited intervals to the current suffix as we go. */
while ((super_ref = intervals[ref & POS_MASK]) & LCP_MASK) {
intervals[ref & POS_MASK] = nOffset;
ref = super_ref;
}
if (super_ref == 0) {
/* In this case, the current interval may be any of:
* (1) the root;
* (2) an unvisited child of the root;
* (3) an interval last visited by suffix 0
*
* We could avoid the ambiguity with (3) by using an lcp
* placeholder value other than 0 to represent "visited", but
* it's fastest to use 0. So we just don't allow matches with
* position 0. */
if (ref != 0) /* Not the root? */
intervals[ref & POS_MASK] = nOffset;
return 0;
}
/* Ascend indirectly via pos_data[] links. */
match_pos = super_ref;
matchptr = pMatches;
for (;;) {
while ((super_ref = pos_data[match_pos]) > ref)
match_pos = intervals[super_ref & POS_MASK];
intervals[ref & POS_MASK] = nOffset;
pos_data[match_pos] = ref;
if ((matchptr - pMatches) < nMaxMatches) {
int nMatchOffset = (int)(nOffset - match_pos);
if (nMatchOffset <= MAX_OFFSET) {
matchptr->length = (unsigned short)(ref >> LCP_SHIFT);
matchptr->offset = (unsigned short)nMatchOffset;
matchptr++;
}
}
if (super_ref == 0)
break;
ref = super_ref;
match_pos = intervals[ref & POS_MASK];
}
return (int)(matchptr - pMatches);
}
/**
* Skip previously compressed bytes
*
* @param pCompressor compression context
* @param nStartOffset current offset in input window (typically 0)
* @param nEndOffset offset to skip to in input window (typically the number of previously compressed bytes)
*/
static void lzsa_skip_matches(lsza_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
lzsa_match match;
int i;
/* Skipping still requires scanning for matches, as this also performs a lazy update of the intervals. However,
* we don't store the matches. */
for (i = nStartOffset; i < nEndOffset; i++) {
lzsa_find_matches_at(pCompressor, i, &match, 0);
}
}
/**
* Find all matches for the data to be compressed. Up to NMATCHES_PER_OFFSET matches are stored for each offset, for
* the optimizer to look at.
*
* @param pCompressor compression context
* @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
*/
static void lzsa_find_all_matches(lsza_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
lzsa_match *pMatch = pCompressor->match + (nStartOffset << MATCHES_PER_OFFSET_SHIFT);
int i;
for (i = nStartOffset; i < nEndOffset; i++) {
int nMatches = lzsa_find_matches_at(pCompressor, i, pMatch, NMATCHES_PER_OFFSET);
int m;
for (m = 0; m < NMATCHES_PER_OFFSET; m++) {
if (nMatches <= m || i > (nEndOffset - LAST_MATCH_OFFSET)) {
pMatch->length = 0;
pMatch->offset = 0;
}
else {
int nMaxLen = (nEndOffset - LAST_LITERALS) - i;
if (nMaxLen < 0)
nMaxLen = 0;
if (pMatch->length > nMaxLen)
pMatch->length = (unsigned short)nMaxLen;
}
pMatch++;
}
}
}
/**
* Get the number of extra bits required to represent a literals length
*
* @param nLength literals length
*
* @return number of extra bits required
*/
static inline int lzsa_get_literals_varlen_size(const int nLength) {
if (nLength < LITERALS_RUN_LEN) {
return 0;
}
else {
if (nLength < 256)
return 8;
else {
if (nLength < 512)
return 16;
else
return 24;
}
}
}
/**
* Write extra literals length bytes to output (compressed) buffer. The caller must first check that there is enough
* room to write the bytes.
*
* @param pOutData pointer to output buffer
* @param nOutOffset current write index into output buffer
* @param nLength literals length
*/
static inline int lzsa_write_literals_varlen(unsigned char *pOutData, int nOutOffset, int nLength) {
if (nLength >= LITERALS_RUN_LEN) {
if (nLength < 256)
pOutData[nOutOffset++] = nLength - LITERALS_RUN_LEN;
else {
if (nLength < 512) {
pOutData[nOutOffset++] = 250;
pOutData[nOutOffset++] = nLength - 256;
}
else {
pOutData[nOutOffset++] = 249;
pOutData[nOutOffset++] = nLength & 0xff;
pOutData[nOutOffset++] = (nLength >> 8) & 0xff;
}
}
}
return nOutOffset;
}
/**
* Get the number of extra bits required to represent an encoded match length
*
* @param nLength encoded match length (actual match length - MIN_MATCH_SIZE)
*
* @return number of extra bits required
*/
static inline int lzsa_get_match_varlen_size(const int nLength) {
if (nLength < MATCH_RUN_LEN) {
return 0;
}
else {
if ((nLength + MIN_MATCH_SIZE) < 256)
return 8;
else {
if ((nLength + MIN_MATCH_SIZE) < 512)
return 16;
else
return 24;
}
}
}
/**
* Write extra encoded match length bytes to output (compressed) buffer. The caller must first check that there is enough
* room to write the bytes.
*
* @param pOutData pointer to output buffer
* @param nOutOffset current write index into output buffer
* @param nLength encoded match length (actual match length - MIN_MATCH_SIZE)
*/
static inline int lzsa_write_match_varlen(unsigned char *pOutData, int nOutOffset, int nLength) {
if (nLength >= MATCH_RUN_LEN) {
if ((nLength + MIN_MATCH_SIZE) < 256)
pOutData[nOutOffset++] = nLength - MATCH_RUN_LEN;
else {
if ((nLength + MIN_MATCH_SIZE) < 512) {
pOutData[nOutOffset++] = 239;
pOutData[nOutOffset++] = nLength + MIN_MATCH_SIZE - 256;
}
else {
pOutData[nOutOffset++] = 238;
pOutData[nOutOffset++] = (nLength + MIN_MATCH_SIZE) & 0xff;
pOutData[nOutOffset++] = ((nLength + MIN_MATCH_SIZE) >> 8) & 0xff;
}
}
}
return nOutOffset;
}
/**
* Attempt to pick optimal matches, so as to produce the smallest possible output that decompresses to the same input
*
* @param pCompressor compression context
* @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
*/
static void lzsa_optimize_matches(lsza_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
int *cost = (int*)pCompressor->pos_data; /* Reuse */
int nLastLiteralsOffset;
int nMinMatchSize = pCompressor->min_match_size;
const int nFavorRatio = (pCompressor->flags & LZSA_FLAG_FAVOR_RATIO) ? 1 : 0;
int i;
cost[nEndOffset - 1] = 8;
nLastLiteralsOffset = nEndOffset;
for (i = nEndOffset - 2; i != (nStartOffset - 1); i--) {
int nBestCost, nBestMatchLen, nBestMatchOffset;
int nLiteralsLen = nLastLiteralsOffset - i;
nBestCost = 8 + cost[i + 1];
if (nLiteralsLen == LITERALS_RUN_LEN || nLiteralsLen == 256 || nLiteralsLen == 512) {
/* Add to the cost of encoding literals as their number crosses a variable length encoding boundary.
* The cost automatically accumulates down the chain. */
nBestCost += 8;
}
if (pCompressor->match[(i + 1) << MATCHES_PER_OFFSET_SHIFT].length >= MIN_MATCH_SIZE)
nBestCost += MODESWITCH_PENALTY;
nBestMatchLen = 0;
nBestMatchOffset = 0;
lzsa_match *pMatch = pCompressor->match + (i << MATCHES_PER_OFFSET_SHIFT);
int m;
for (m = 0; m < NMATCHES_PER_OFFSET && pMatch[m].length >= nMinMatchSize; m++) {
int nMatchOffsetSize = (pMatch[m].offset <= 256) ? 8 : 16;
if (pMatch[m].length >= LEAVE_ALONE_MATCH_SIZE) {
int nCurCost;
int nMatchLen = pMatch[m].length;
if ((i + nMatchLen) > (nEndOffset - LAST_LITERALS))
nMatchLen = nEndOffset - LAST_LITERALS - i;
nCurCost = 8 + nMatchOffsetSize + lzsa_get_match_varlen_size(nMatchLen - MIN_MATCH_SIZE);
nCurCost += cost[i + nMatchLen];
if (pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].length >= MIN_MATCH_SIZE)
nCurCost += MODESWITCH_PENALTY;
if (nBestCost > (nCurCost - nFavorRatio)) {
nBestCost = nCurCost;
nBestMatchLen = nMatchLen;
nBestMatchOffset = pMatch[m].offset;
}
}
else {
int nMatchLen = pMatch[m].length;
int k, nMatchRunLen;
if ((i + nMatchLen) > (nEndOffset - LAST_LITERALS))
nMatchLen = nEndOffset - LAST_LITERALS - i;
nMatchRunLen = nMatchLen;
if (nMatchRunLen > MATCH_RUN_LEN)
nMatchRunLen = MATCH_RUN_LEN;
for (k = nMinMatchSize; k < nMatchRunLen; k++) {
int nCurCost;
nCurCost = 8 + nMatchOffsetSize /* no extra match len bytes */;
nCurCost += cost[i + k];
if (pCompressor->match[(i + k) << MATCHES_PER_OFFSET_SHIFT].length >= MIN_MATCH_SIZE)
nCurCost += MODESWITCH_PENALTY;
if (nBestCost > (nCurCost - nFavorRatio)) {
nBestCost = nCurCost;
nBestMatchLen = k;
nBestMatchOffset = pMatch[m].offset;
}
}
for (; k <= nMatchLen; k++) {
int nCurCost;
nCurCost = 8 + nMatchOffsetSize + lzsa_get_match_varlen_size(k - MIN_MATCH_SIZE);
nCurCost += cost[i + k];
if (pCompressor->match[(i + k) << MATCHES_PER_OFFSET_SHIFT].length >= MIN_MATCH_SIZE)
nCurCost += MODESWITCH_PENALTY;
if (nBestCost > (nCurCost - nFavorRatio)) {
nBestCost = nCurCost;
nBestMatchLen = k;
nBestMatchOffset = pMatch[m].offset;
}
}
}
}
if (nBestMatchLen >= MIN_MATCH_SIZE)
nLastLiteralsOffset = i;
cost[i] = nBestCost;
pMatch->length = nBestMatchLen;
pMatch->offset = nBestMatchOffset;
}
}
/**
* Attempt to minimize the number of commands issued in the compressed data block, in order to speed up decompression without
* impacting the compression ratio
*
* @param pCompressor compression context
* @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
*
* @return non-zero if the number of tokens was reduced, 0 if it wasn't
*/
static int lzsa_optimize_command_count(lsza_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
int i;
int nNumLiterals = 0;
int nDidReduce = 0;
for (i = nStartOffset; i < nEndOffset; ) {
lzsa_match *pMatch = pCompressor->match + (i << MATCHES_PER_OFFSET_SHIFT);
if (pMatch->length >= MIN_MATCH_SIZE) {
int nMatchLen = pMatch->length;
int nReduce = 0;
if (nMatchLen <= 9 && (i + nMatchLen) < nEndOffset) /* max reducable command size: <token> <EE> <ll> <ll> <offset> <offset> <EE> <mm> <mm> */ {
int nMatchOffset = pMatch->offset;
int nEncodedMatchLen = nMatchLen - MIN_MATCH_SIZE;
int nCommandSize = 8 /* token */ + lzsa_get_literals_varlen_size(nNumLiterals) + ((nMatchOffset <= 256) ? 8 : 16) /* match offset */ + lzsa_get_match_varlen_size(nEncodedMatchLen);
if (pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].length >= MIN_MATCH_SIZE) {
if (nCommandSize >= ((nMatchLen << 3) + lzsa_get_literals_varlen_size(nNumLiterals + nMatchLen))) {
/* This command is a match; the next command is also a match. The next command currently has no literals; replacing this command by literals will
* make the next command eat the cost of encoding the current number of literals, + nMatchLen extra literals. The size of the current match command is
* at least as much as the number of literal bytes + the extra cost of encoding them in the next match command, so we can safely replace the current
* match command by literals, the output size will not increase and it will remove one command. */
nReduce = 1;
}
}
else {
int nCurIndex = i + nMatchLen;
int nNextNumLiterals = 0;
do {
nCurIndex++;
nNextNumLiterals++;
} while (nCurIndex < nEndOffset && pCompressor->match[nCurIndex << MATCHES_PER_OFFSET_SHIFT].length < MIN_MATCH_SIZE);
if (nCommandSize >= ((nMatchLen << 3) + lzsa_get_literals_varlen_size(nNumLiterals + nNextNumLiterals + nMatchLen) - lzsa_get_literals_varlen_size(nNextNumLiterals))) {
/* This command is a match, and is followed by literals, and then another match or the end of the input data. If encoding this match as literals doesn't take
* more room than the match, and doesn't grow the next match command's literals encoding, go ahead and remove the command. */
nReduce = 1;
}
}
}
if (nReduce) {
int j;
for (j = 0; j < nMatchLen; j++) {
pCompressor->match[(i + j) << MATCHES_PER_OFFSET_SHIFT].length = 0;
}
nNumLiterals += nMatchLen;
i += nMatchLen;
nDidReduce = 1;
}
else {
if ((i + nMatchLen) < nEndOffset && nMatchLen >= LCP_MAX &&
pMatch->offset && pMatch->offset <= 32 && pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].offset == pMatch->offset && (nMatchLen % pMatch->offset) == 0 &&
(nMatchLen + pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].length) <= MAX_OFFSET) {
/* Join */
pMatch->length += pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].length;
pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].offset = 0;
pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].length = -1;
continue;
}
nNumLiterals = 0;
i += nMatchLen;
}
}
else {
nNumLiterals++;
i++;
}
}
return nDidReduce;
}
/**
* Emit block of compressed data
*
* @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 pOutData pointer to output buffer
* @param nMaxOutDataSize maximum size of output buffer, in bytes
*
* @return size of compressed data in output buffer, or -1 if the data is uncompressible
*/
static int lzsa_write_block(lsza_compressor *pCompressor, const unsigned char *pInWindow, const int nStartOffset, const int nEndOffset, unsigned char *pOutData, const int nMaxOutDataSize) {
int i;
int nNumLiterals = 0;
int nInFirstLiteralOffset = 0;
int nOutOffset = 0;
for (i = nStartOffset; i < nEndOffset; ) {
lzsa_match *pMatch = pCompressor->match + (i << MATCHES_PER_OFFSET_SHIFT);
if (pMatch->length >= MIN_MATCH_SIZE) {
int nMatchOffset = pMatch->offset;
int nMatchLen = pMatch->length;
int nEncodedMatchLen = nMatchLen - MIN_MATCH_SIZE;
int nTokenLiteralsLen = (nNumLiterals >= LITERALS_RUN_LEN) ? LITERALS_RUN_LEN : nNumLiterals;
int nTokenMatchLen = (nEncodedMatchLen >= MATCH_RUN_LEN) ? MATCH_RUN_LEN : nEncodedMatchLen;
int nTokenLongOffset = (nMatchOffset <= 256) ? 0x00 : 0x80;
int nCommandSize = 8 /* token */ + lzsa_get_literals_varlen_size(nNumLiterals) + (nNumLiterals << 3) + (nTokenLongOffset ? 16 : 8) /* match offset */ + lzsa_get_match_varlen_size(nEncodedMatchLen);
if ((nOutOffset + (nCommandSize >> 3)) > nMaxOutDataSize)
return -1;
if (nMatchOffset < MIN_OFFSET || nMatchOffset > MAX_OFFSET)
return -1;
pOutData[nOutOffset++] = nTokenLongOffset | (nTokenLiteralsLen << 4) | nTokenMatchLen;
nOutOffset = lzsa_write_literals_varlen(pOutData, nOutOffset, nNumLiterals);
if (nNumLiterals != 0) {
memcpy(pOutData + nOutOffset, pInWindow + nInFirstLiteralOffset, nNumLiterals);
nOutOffset += nNumLiterals;
nNumLiterals = 0;
}
pOutData[nOutOffset++] = (-nMatchOffset) & 0xff;
if (nTokenLongOffset) {
pOutData[nOutOffset++] = (-nMatchOffset) >> 8;
}
nOutOffset = lzsa_write_match_varlen(pOutData, nOutOffset, nEncodedMatchLen);
i += nMatchLen;
pCompressor->num_commands++;
}
else {
if (nNumLiterals == 0)
nInFirstLiteralOffset = i;
nNumLiterals++;
i++;
}
}
{
int nTokenLiteralsLen = (nNumLiterals >= LITERALS_RUN_LEN) ? LITERALS_RUN_LEN : nNumLiterals;
int nCommandSize = 8 /* token */ + lzsa_get_literals_varlen_size(nNumLiterals) + (nNumLiterals << 3);
if ((nOutOffset + (nCommandSize >> 3)) > nMaxOutDataSize)
return -1;
if (pCompressor->flags & LZSA_FLAG_RAW_BLOCK)
pOutData[nOutOffset++] = (nTokenLiteralsLen << 4) | 0x0f;
else
pOutData[nOutOffset++] = (nTokenLiteralsLen << 4) | 0x00;
nOutOffset = lzsa_write_literals_varlen(pOutData, nOutOffset, nNumLiterals);
if (nNumLiterals != 0) {
memcpy(pOutData + nOutOffset, pInWindow + nInFirstLiteralOffset, nNumLiterals);
nOutOffset += nNumLiterals;
nNumLiterals = 0;
}
pCompressor->num_commands++;
}
if (pCompressor->flags & LZSA_FLAG_RAW_BLOCK) {
/* Emit EOD marker for raw block */
if ((nOutOffset + 4) > nMaxOutDataSize)
return -1;
pOutData[nOutOffset++] = 0;
pOutData[nOutOffset++] = 238;
pOutData[nOutOffset++] = 0;
pOutData[nOutOffset++] = 0;
}
return nOutOffset;
}
/**
* Compress one block of data
*
* @param pCompressor compression context
* @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
* @param nPreviousBlockSize number of previously compressed bytes (or 0 for none)
* @param nInDataSize number of input bytes to compress
* @param pOutData pointer to output buffer
* @param nMaxOutDataSize maximum size of output buffer, in bytes
*
* @return size of compressed data in output buffer, or -1 if the data is uncompressible
*/
int lzsa_shrink_block(lsza_compressor *pCompressor, const unsigned char *pInWindow, const int nPreviousBlockSize, const int nInDataSize, unsigned char *pOutData, const int nMaxOutDataSize) {
if (lzsa_build_suffix_array(pCompressor, pInWindow, nPreviousBlockSize + nInDataSize))
return -1;
if (nPreviousBlockSize) {
lzsa_skip_matches(pCompressor, 0, nPreviousBlockSize);
}
lzsa_find_all_matches(pCompressor, nPreviousBlockSize, nPreviousBlockSize + nInDataSize);
lzsa_optimize_matches(pCompressor, nPreviousBlockSize, nPreviousBlockSize + nInDataSize);
int nDidReduce;
int nPasses = 0;
do {
nDidReduce = lzsa_optimize_command_count(pCompressor, nPreviousBlockSize, nPreviousBlockSize + nInDataSize);
nPasses++;
} while (nDidReduce && nPasses < 20);
return lzsa_write_block(pCompressor, pInWindow, nPreviousBlockSize, nPreviousBlockSize + nInDataSize, pOutData, nMaxOutDataSize);
}
/**
* Get the number of compression commands issued in compressed data blocks
*
* @return number of commands
*/
int lzsa_compressor_get_command_count(lsza_compressor *pCompressor) {
return pCompressor->num_commands;
}
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