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lzsa/src/matchfinder.c

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/*
* matchfinder.c - LZ match finder implementation
*
* The following copying information applies to this specific source code file:
*
* Written in 2019 by Emmanuel Marty <marty.emmanuel@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 help, ideas, optimizations and speed measurements by spke <zxintrospec@gmail.com>
* 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 "matchfinder.h"
#include "format.h"
#include "lib.h"
/**
* 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
*/
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
*/
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)
*/
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
*/
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++;
}
}
}
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