2019-05-09 14:51:29 +00:00
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/*
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* matchfinder.c - LZ match finder implementation
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*
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* The following copying information applies to this specific source code file:
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*
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* Written in 2019 by Emmanuel Marty <marty.emmanuel@gmail.com>
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* Portions written in 2014-2015 by Eric Biggers <ebiggers3@gmail.com>
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*
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* To the extent possible under law, the author(s) have dedicated all copyright
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* and related and neighboring rights to this software to the public domain
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* worldwide via the Creative Commons Zero 1.0 Universal Public Domain
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* Dedication (the "CC0").
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*
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* This software is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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* FOR A PARTICULAR PURPOSE. See the CC0 for more details.
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*
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* You should have received a copy of the CC0 along with this software; if not
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* see <http://creativecommons.org/publicdomain/zero/1.0/>.
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*/
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/*
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* Uses the libdivsufsort library Copyright (c) 2003-2008 Yuta Mori
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*
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* Inspired by LZ4 by Yann Collet. https://github.com/lz4/lz4
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* With help, ideas, optimizations and speed measurements by spke <zxintrospec@gmail.com>
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* With ideas from Lizard by Przemyslaw Skibinski and Yann Collet. https://github.com/inikep/lizard
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* Also with ideas from smallz4 by Stephan Brumme. https://create.stephan-brumme.com/smallz4/
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*
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*/
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#include <stdlib.h>
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#include <string.h>
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#include "matchfinder.h"
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#include "format.h"
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#include "lib.h"
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/**
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* Parse input data, build suffix array and overlaid data structures to speed up match finding
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*
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* @param pCompressor compression context
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* @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
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* @param nInWindowSize total input size in bytes (previously compressed bytes + bytes to compress)
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*
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* @return 0 for success, non-zero for failure
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*/
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2019-06-07 21:15:40 +00:00
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int lzsa_build_suffix_array(lzsa_compressor *pCompressor, const unsigned char *pInWindow, const int nInWindowSize) {
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2019-05-09 14:51:29 +00:00
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unsigned int *intervals = pCompressor->intervals;
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/* Build suffix array from input data */
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if (divsufsort_build_array(&pCompressor->divsufsort_context, pInWindow, (saidx_t*)intervals, nInWindowSize) != 0) {
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return 100;
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}
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int *PLCP = (int*)pCompressor->pos_data; /* Use temporarily */
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int *Phi = PLCP;
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int nCurLen = 0;
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int i;
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/* Compute the permuted LCP first (K<>rkk<6B>inen method) */
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Phi[intervals[0]] = -1;
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for (i = 1; i < nInWindowSize; i++)
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Phi[intervals[i]] = intervals[i - 1];
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for (i = 0; i < nInWindowSize; i++) {
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if (Phi[i] == -1) {
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PLCP[i] = 0;
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continue;
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}
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int nMaxLen = (i > Phi[i]) ? (nInWindowSize - i) : (nInWindowSize - Phi[i]);
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while (nCurLen < nMaxLen && pInWindow[i + nCurLen] == pInWindow[Phi[i] + nCurLen]) nCurLen++;
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PLCP[i] = nCurLen;
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if (nCurLen > 0)
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nCurLen--;
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}
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/* Rotate permuted LCP into the LCP. This has better cache locality than the direct Kasai LCP method. This also
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* saves us from having to build the inverse suffix array index, as the LCP is calculated without it using this method,
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* and the interval builder below doesn't need it either. */
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intervals[0] &= POS_MASK;
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int nMinMatchSize = pCompressor->min_match_size;
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for (i = 1; i < nInWindowSize - 1; i++) {
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int nIndex = (int)(intervals[i] & POS_MASK);
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int nLen = PLCP[nIndex];
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if (nLen < nMinMatchSize)
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nLen = 0;
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if (nLen > LCP_MAX)
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nLen = LCP_MAX;
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intervals[i] = ((unsigned int)nIndex) | (((unsigned int)nLen) << LCP_SHIFT);
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}
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if (i < nInWindowSize)
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intervals[i] &= POS_MASK;
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/**
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* Build intervals for finding matches
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*
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* Methodology and code fragment taken from wimlib (CC0 license):
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* https://wimlib.net/git/?p=wimlib;a=blob_plain;f=src/lcpit_matchfinder.c;h=a2d6a1e0cd95200d1f3a5464d8359d5736b14cbe;hb=HEAD
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*/
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unsigned int * const SA_and_LCP = intervals;
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unsigned int *pos_data = pCompressor->pos_data;
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unsigned int next_interval_idx;
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unsigned int *top = pCompressor->open_intervals;
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unsigned int prev_pos = SA_and_LCP[0] & POS_MASK;
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*top = 0;
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intervals[0] = 0;
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next_interval_idx = 1;
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for (int r = 1; r < nInWindowSize; r++) {
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const unsigned int next_pos = SA_and_LCP[r] & POS_MASK;
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const unsigned int next_lcp = SA_and_LCP[r] & LCP_MASK;
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const unsigned int top_lcp = *top & LCP_MASK;
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if (next_lcp == top_lcp) {
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/* Continuing the deepest open interval */
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pos_data[prev_pos] = *top;
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}
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else if (next_lcp > top_lcp) {
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/* Opening a new interval */
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*++top = next_lcp | next_interval_idx++;
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pos_data[prev_pos] = *top;
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}
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else {
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/* Closing the deepest open interval */
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pos_data[prev_pos] = *top;
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for (;;) {
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const unsigned int closed_interval_idx = *top-- & POS_MASK;
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const unsigned int superinterval_lcp = *top & LCP_MASK;
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if (next_lcp == superinterval_lcp) {
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/* Continuing the superinterval */
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intervals[closed_interval_idx] = *top;
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break;
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}
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else if (next_lcp > superinterval_lcp) {
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/* Creating a new interval that is a
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* superinterval of the one being
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* closed, but still a subinterval of
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* its superinterval */
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*++top = next_lcp | next_interval_idx++;
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intervals[closed_interval_idx] = *top;
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break;
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}
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else {
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/* Also closing the superinterval */
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intervals[closed_interval_idx] = *top;
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}
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}
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}
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prev_pos = next_pos;
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}
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/* Close any still-open intervals. */
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pos_data[prev_pos] = *top;
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for (; top > pCompressor->open_intervals; top--)
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intervals[*top & POS_MASK] = *(top - 1);
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/* Success */
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return 0;
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}
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/**
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* Find matches at the specified offset in the input window
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*
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* @param pCompressor compression context
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* @param nOffset offset to find matches at, in the input window
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* @param pMatches pointer to returned matches
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* @param nMaxMatches maximum number of matches to return (0 for none)
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*
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* @return number of matches
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*/
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2019-06-07 21:15:40 +00:00
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int lzsa_find_matches_at(lzsa_compressor *pCompressor, const int nOffset, lzsa_match *pMatches, const int nMaxMatches) {
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2019-05-09 14:51:29 +00:00
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unsigned int *intervals = pCompressor->intervals;
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unsigned int *pos_data = pCompressor->pos_data;
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unsigned int ref;
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unsigned int super_ref;
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unsigned int match_pos;
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lzsa_match *matchptr;
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/**
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* Find matches using intervals
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*
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* Taken from wimlib (CC0 license):
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* https://wimlib.net/git/?p=wimlib;a=blob_plain;f=src/lcpit_matchfinder.c;h=a2d6a1e0cd95200d1f3a5464d8359d5736b14cbe;hb=HEAD
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*/
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/* Get the deepest lcp-interval containing the current suffix. */
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ref = pos_data[nOffset];
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pos_data[nOffset] = 0;
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/* Ascend until we reach a visited interval, the root, or a child of the
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* root. Link unvisited intervals to the current suffix as we go. */
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while ((super_ref = intervals[ref & POS_MASK]) & LCP_MASK) {
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intervals[ref & POS_MASK] = nOffset;
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ref = super_ref;
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}
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if (super_ref == 0) {
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/* In this case, the current interval may be any of:
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* (1) the root;
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* (2) an unvisited child of the root;
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* (3) an interval last visited by suffix 0
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*
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* We could avoid the ambiguity with (3) by using an lcp
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* placeholder value other than 0 to represent "visited", but
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* it's fastest to use 0. So we just don't allow matches with
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* position 0. */
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if (ref != 0) /* Not the root? */
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intervals[ref & POS_MASK] = nOffset;
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return 0;
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}
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/* Ascend indirectly via pos_data[] links. */
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match_pos = super_ref;
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matchptr = pMatches;
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for (;;) {
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while ((super_ref = pos_data[match_pos]) > ref)
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match_pos = intervals[super_ref & POS_MASK];
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intervals[ref & POS_MASK] = nOffset;
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pos_data[match_pos] = ref;
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if ((matchptr - pMatches) < nMaxMatches) {
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int nMatchOffset = (int)(nOffset - match_pos);
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if (nMatchOffset <= MAX_OFFSET) {
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matchptr->length = (unsigned short)(ref >> LCP_SHIFT);
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matchptr->offset = (unsigned short)nMatchOffset;
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matchptr++;
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}
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}
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if (super_ref == 0)
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break;
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ref = super_ref;
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match_pos = intervals[ref & POS_MASK];
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}
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return (int)(matchptr - pMatches);
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}
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/**
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* Skip previously compressed bytes
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*
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* @param pCompressor compression context
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* @param nStartOffset current offset in input window (typically 0)
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* @param nEndOffset offset to skip to in input window (typically the number of previously compressed bytes)
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*/
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2019-06-07 21:15:40 +00:00
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void lzsa_skip_matches(lzsa_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
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2019-05-09 14:51:29 +00:00
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lzsa_match match;
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int i;
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/* Skipping still requires scanning for matches, as this also performs a lazy update of the intervals. However,
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* we don't store the matches. */
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for (i = nStartOffset; i < nEndOffset; i++) {
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lzsa_find_matches_at(pCompressor, i, &match, 0);
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}
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}
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/**
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* Find all matches for the data to be compressed. Up to NMATCHES_PER_OFFSET matches are stored for each offset, for
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* the optimizer to look at.
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*
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* @param pCompressor compression context
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* @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
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* @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
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*/
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2019-06-07 21:15:40 +00:00
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void lzsa_find_all_matches(lzsa_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
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2019-05-09 14:51:29 +00:00
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lzsa_match *pMatch = pCompressor->match + (nStartOffset << MATCHES_PER_OFFSET_SHIFT);
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int i;
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for (i = nStartOffset; i < nEndOffset; i++) {
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int nMatches = lzsa_find_matches_at(pCompressor, i, pMatch, NMATCHES_PER_OFFSET);
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int m;
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for (m = 0; m < NMATCHES_PER_OFFSET; m++) {
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if (nMatches <= m || i > (nEndOffset - LAST_MATCH_OFFSET)) {
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pMatch->length = 0;
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pMatch->offset = 0;
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}
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else {
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int nMaxLen = (nEndOffset - LAST_LITERALS) - i;
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if (nMaxLen < 0)
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nMaxLen = 0;
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if (pMatch->length > nMaxLen)
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pMatch->length = (unsigned short)nMaxLen;
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}
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pMatch++;
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}
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}
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}
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