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// SPDX-License-Identifier: 0BSD
///////////////////////////////////////////////////////////////////////////////
//
/// \file lzma_encoder_optimum_fast.c
//
// Author: Igor Pavlov
//
///////////////////////////////////////////////////////////////////////////////
#include "lzma_encoder_private.h"
#include "memcmplen.h"
#define change_pair(small_dist, big_dist) \
(((big_dist) >> 7) > (small_dist))
extern void
lzma_lzma_optimum_fast(lzma_lzma1_encoder *restrict coder,
lzma_mf *restrict mf,
uint32_t *restrict back_res, uint32_t *restrict len_res)
{
const uint32_t nice_len = mf->nice_len;
uint32_t len_main;
uint32_t matches_count;
if (mf->read_ahead == 0) {
len_main = mf_find(mf, &matches_count, coder->matches);
} else {
assert(mf->read_ahead == 1);
len_main = coder->longest_match_length;
matches_count = coder->matches_count;
}
const uint8_t *buf = mf_ptr(mf) - 1;
const uint32_t buf_avail = my_min(mf_avail(mf) + 1, MATCH_LEN_MAX);
if (buf_avail < 2) {
// There's not enough input left to encode a match.
*back_res = UINT32_MAX;
*len_res = 1;
return;
}
// Look for repeated matches; scan the previous four match distances
uint32_t rep_len = 0;
uint32_t rep_index = 0;
for (uint32_t i = 0; i < REPS; ++i) {
// Pointer to the beginning of the match candidate
const uint8_t *const buf_back = buf - coder->reps[i] - 1;
// If the first two bytes (2 == MATCH_LEN_MIN) do not match,
// this rep is not useful.
if (not_equal_16(buf, buf_back))
continue;
// The first two bytes matched.
// Calculate the length of the match.
const uint32_t len = lzma_memcmplen(
buf, buf_back, 2, buf_avail);
// If we have found a repeated match that is at least
// nice_len long, return it immediately.
if (len >= nice_len) {
*back_res = i;
*len_res = len;
mf_skip(mf, len - 1);
return;
}
if (len > rep_len) {
rep_index = i;
rep_len = len;
}
}
// We didn't find a long enough repeated match. Encode it as a normal
// match if the match length is at least nice_len.
if (len_main >= nice_len) {
*back_res = coder->matches[matches_count - 1].dist + REPS;
*len_res = len_main;
mf_skip(mf, len_main - 1);
return;
}
uint32_t back_main = 0;
if (len_main >= 2) {
back_main = coder->matches[matches_count - 1].dist;
while (matches_count > 1 && len_main ==
coder->matches[matches_count - 2].len + 1) {
if (!change_pair(coder->matches[
matches_count - 2].dist,
back_main))
break;
--matches_count;
len_main = coder->matches[matches_count - 1].len;
back_main = coder->matches[matches_count - 1].dist;
}
if (len_main == 2 && back_main >= 0x80)
len_main = 1;
}
if (rep_len >= 2) {
if (rep_len + 1 >= len_main
|| (rep_len + 2 >= len_main
&& back_main > (UINT32_C(1) << 9))
|| (rep_len + 3 >= len_main
&& back_main > (UINT32_C(1) << 15))) {
*back_res = rep_index;
*len_res = rep_len;
mf_skip(mf, rep_len - 1);
return;
}
}
if (len_main < 2 || buf_avail <= 2) {
*back_res = UINT32_MAX;
*len_res = 1;
return;
}
// Get the matches for the next byte. If we find a better match,
// the current byte is encoded as a literal.
coder->longest_match_length = mf_find(mf,
&coder->matches_count, coder->matches);
if (coder->longest_match_length >= 2) {
const uint32_t new_dist = coder->matches[
coder->matches_count - 1].dist;
if ((coder->longest_match_length >= len_main
&& new_dist < back_main)
|| (coder->longest_match_length == len_main + 1
&& !change_pair(back_main, new_dist))
|| (coder->longest_match_length > len_main + 1)
|| (coder->longest_match_length + 1 >= len_main
&& len_main >= 3
&& change_pair(new_dist, back_main))) {
*back_res = UINT32_MAX;
*len_res = 1;
return;
}
}
// In contrast to LZMA SDK, dictionary could not have been moved
// between mf_find() calls, thus it is safe to just increment
// the old buf pointer instead of recalculating it with mf_ptr().
++buf;
const uint32_t limit = my_max(2, len_main - 1);
for (uint32_t i = 0; i < REPS; ++i) {
if (memcmp(buf, buf - coder->reps[i] - 1, limit) == 0) {
*back_res = UINT32_MAX;
*len_res = 1;
return;
}
}
*back_res = back_main + REPS;
*len_res = len_main;
mf_skip(mf, len_main - 2);
return;
}
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