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///////////////////////////////////////////////////////////////////////////////
//
/// \file lzma_encoder_getoptimumfast.c
//
// Copyright (C) 1999-2006 Igor Pavlov
// Copyright (C) 2007 Lasse Collin
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library 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 GNU
// Lesser General Public License for more details.
//
///////////////////////////////////////////////////////////////////////////////
// NOTE: If you want to keep the line length in 80 characters, set
// tab width to 4 or less in your editor when editing this file.
#include "lzma_encoder_private.h"
#define change_pair(small_dist, big_dist) \
(((big_dist) >> 7) > (small_dist))
extern void
lzma_get_optimum_fast(lzma_coder *restrict coder,
uint32_t *restrict back_res, uint32_t *restrict len_res)
{
// Local copies
const uint32_t fast_bytes = coder->fast_bytes;
uint32_t len_main;
uint32_t num_distance_pairs;
if (!coder->longest_match_was_found) {
lzma_read_match_distances(coder, &len_main, &num_distance_pairs);
} else {
len_main = coder->longest_match_length;
num_distance_pairs = coder->num_distance_pairs;
coder->longest_match_was_found = false;
}
const uint8_t *buf = coder->lz.buffer + coder->lz.read_pos - 1;
uint32_t num_available_bytes
= coder->lz.write_pos - coder->lz.read_pos + 1;
if (num_available_bytes < 2) {
// There's not enough input left to encode a match.
*back_res = UINT32_MAX;
*len_res = 1;
return;
}
if (num_available_bytes > MATCH_MAX_LEN)
num_available_bytes = MATCH_MAX_LEN;
// Look for repetitive matches; scan the previous four match distances
uint32_t rep_lens[REP_DISTANCES];
uint32_t rep_max_index = 0;
for (uint32_t i = 0; i < REP_DISTANCES; ++i) {
const uint32_t back_offset = coder->reps[i] + 1;
// If the first two bytes (2 == MATCH_MIN_LEN) do not match,
// this rep_distance[i] is not useful. This is indicated
// using zero as the length of the repetitive match.
if (buf[0] != *(buf - back_offset)
|| buf[1] != *(buf + 1 - back_offset)) {
rep_lens[i] = 0;
continue;
}
// The first two bytes matched.
// Calculate the length of the match.
uint32_t len;
for (len = 2; len < num_available_bytes
&& buf[len] == *(buf + len - back_offset);
++len) ;
// If we have found a repetitive match that is at least
// as long as fast_bytes, return it immediatelly.
if (len >= fast_bytes) {
*back_res = i;
*len_res = len;
move_pos(len - 1);
return;
}
rep_lens[i] = len;
// After this loop, rep_lens[rep_max_index] is the biggest
// value of all values in rep_lens[].
if (len > rep_lens[rep_max_index])
rep_max_index = i;
}
if (len_main >= fast_bytes) {
*back_res = coder->match_distances[num_distance_pairs]
+ REP_DISTANCES;
*len_res = len_main;
move_pos(len_main - 1);
return;
}
uint32_t back_main = 0;
if (len_main >= 2) {
back_main = coder->match_distances[num_distance_pairs];
while (num_distance_pairs > 2 && len_main ==
coder->match_distances[num_distance_pairs - 3] + 1) {
if (!change_pair(coder->match_distances[
num_distance_pairs - 2], back_main))
break;
num_distance_pairs -= 2;
len_main = coder->match_distances[num_distance_pairs - 1];
back_main = coder->match_distances[num_distance_pairs];
}
if (len_main == 2 && back_main >= 0x80)
len_main = 1;
}
if (rep_lens[rep_max_index] >= 2) {
if (rep_lens[rep_max_index] + 1 >= len_main
|| (rep_lens[rep_max_index] + 2 >= len_main
&& (back_main > (1 << 9)))
|| (rep_lens[rep_max_index] + 3 >= len_main
&& (back_main > (1 << 15)))) {
*back_res = rep_max_index;
*len_res = rep_lens[rep_max_index];
move_pos(*len_res - 1);
return;
}
}
if (len_main >= 2 && num_available_bytes > 2) {
lzma_read_match_distances(coder, &coder->longest_match_length,
&coder->num_distance_pairs);
if (coder->longest_match_length >= 2) {
const uint32_t new_distance = coder->match_distances[
coder->num_distance_pairs];
if ((coder->longest_match_length >= len_main
&& new_distance < back_main)
|| (coder->longest_match_length == len_main + 1
&& !change_pair(back_main, new_distance))
|| (coder->longest_match_length > len_main + 1)
|| (coder->longest_match_length + 1 >= len_main
&& len_main >= 3
&& change_pair(new_distance, back_main))) {
coder->longest_match_was_found = true;
*back_res = UINT32_MAX;
*len_res = 1;
return;
}
}
++buf;
--num_available_bytes;
for (uint32_t i = 0; i < REP_DISTANCES; ++i) {
const uint32_t back_offset = coder->reps[i] + 1;
if (buf[1] != *(buf + 1 - back_offset)
|| buf[2] != *(buf + 2 - back_offset)) {
rep_lens[i] = 0;
continue;
}
uint32_t len;
for (len = 2; len < num_available_bytes
&& buf[len] == *(buf + len - back_offset);
++len) ;
if (len + 1 >= len_main) {
coder->longest_match_was_found = true;
*back_res = UINT32_MAX;
*len_res = 1;
return;
}
}
*back_res = back_main + REP_DISTANCES;
*len_res = len_main;
move_pos(len_main - 2);
return;
}
*back_res = UINT32_MAX;
*len_res = 1;
return;
}
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