mirror of
https://github.com/google/brotli.git
synced 2024-11-22 11:40:06 +00:00
378 lines
15 KiB
C++
378 lines
15 KiB
C++
// Copyright 2013 Google Inc. All Rights Reserved.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
//
|
|
// Function to find backward reference copies.
|
|
|
|
#include "./backward_references.h"
|
|
|
|
#include <algorithm>
|
|
#include <vector>
|
|
|
|
#include "./command.h"
|
|
|
|
namespace brotli {
|
|
|
|
template<typename Hasher, bool kUseCostModel, bool kUseDictionary>
|
|
void CreateBackwardReferences(size_t num_bytes,
|
|
size_t position,
|
|
const uint8_t* ringbuffer,
|
|
size_t ringbuffer_mask,
|
|
const float* literal_cost,
|
|
size_t literal_cost_mask,
|
|
const size_t max_backward_limit,
|
|
const double base_min_score,
|
|
const int quality,
|
|
Hasher* hasher,
|
|
int* dist_cache,
|
|
int* last_insert_len,
|
|
Command* commands,
|
|
int* num_commands,
|
|
int* num_literals) {
|
|
if (num_bytes >= 3 && position >= 3) {
|
|
// Prepare the hashes for three last bytes of the last write.
|
|
// These could not be calculated before, since they require knowledge
|
|
// of both the previous and the current block.
|
|
hasher->Store(&ringbuffer[(position - 3) & ringbuffer_mask],
|
|
position - 3);
|
|
hasher->Store(&ringbuffer[(position - 2) & ringbuffer_mask],
|
|
position - 2);
|
|
hasher->Store(&ringbuffer[(position - 1) & ringbuffer_mask],
|
|
position - 1);
|
|
}
|
|
const Command * const orig_commands = commands;
|
|
int insert_length = *last_insert_len;
|
|
size_t i = position & ringbuffer_mask;
|
|
const int i_diff = position - i;
|
|
const size_t i_end = i + num_bytes;
|
|
|
|
// For speed up heuristics for random data.
|
|
const int random_heuristics_window_size = quality < 9 ? 64 : 512;
|
|
int apply_random_heuristics = i + random_heuristics_window_size;
|
|
|
|
double average_cost = 5.4;
|
|
if (kUseCostModel) {
|
|
average_cost = 0.0;
|
|
for (int k = position; k < position + num_bytes; ++k) {
|
|
average_cost += literal_cost[k & literal_cost_mask];
|
|
}
|
|
if (num_bytes > 0) {
|
|
average_cost /= num_bytes;
|
|
}
|
|
}
|
|
|
|
// M1 match is for considering for two repeated copies, if moving
|
|
// one literal form the previous copy to the current one allows the
|
|
// current copy to be more efficient (because the way static dictionary
|
|
// codes words). M1 matching improves text compression density by ~0.15 %.
|
|
bool match_found_M1 = false;
|
|
int best_len_M1 = 0;
|
|
int best_len_code_M1 = 0;
|
|
int best_dist_M1 = 0;
|
|
double best_score_M1 = 0;
|
|
while (i + 3 < i_end) {
|
|
int max_length = i_end - i;
|
|
size_t max_distance = std::min(i + i_diff, max_backward_limit);
|
|
double min_score = base_min_score;
|
|
if (kUseCostModel && insert_length < 8) {
|
|
double cost_diff[8] =
|
|
{ 0.1, 0.038, 0.019, 0.013, 0.001, 0.001, 0.001, 0.001 };
|
|
min_score += cost_diff[insert_length];
|
|
}
|
|
int best_len = 0;
|
|
int best_len_code = 0;
|
|
int best_dist = 0;
|
|
double best_score = min_score;
|
|
bool match_found = hasher->FindLongestMatch(
|
|
ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, average_cost,
|
|
dist_cache, i + i_diff, max_length, max_distance,
|
|
&best_len, &best_len_code, &best_dist, &best_score);
|
|
if (match_found) {
|
|
if (kUseDictionary && match_found_M1 && best_score_M1 > best_score) {
|
|
// Two copies after each other. Take the last literal from the
|
|
// last copy, and use it as the first of this one.
|
|
Command prev_cmd = commands[-1];
|
|
commands[-1] = Command(prev_cmd.insert_len_,
|
|
prev_cmd.copy_len_ - 1,
|
|
prev_cmd.copy_len_ - 1,
|
|
prev_cmd.DistanceCode());
|
|
hasher->Store(ringbuffer + i, i + i_diff);
|
|
--i;
|
|
best_len = best_len_M1;
|
|
best_len_code = best_len_code_M1;
|
|
best_dist = best_dist_M1;
|
|
best_score = best_score_M1;
|
|
} else {
|
|
// Found a match. Let's look for something even better ahead.
|
|
int delayed_backward_references_in_row = 0;
|
|
for (;;) {
|
|
--max_length;
|
|
int best_len_2 = quality < 4 ? std::min(best_len - 1, max_length) : 0;
|
|
int best_len_code_2 = 0;
|
|
int best_dist_2 = 0;
|
|
double best_score_2 = min_score;
|
|
max_distance = std::min(i + i_diff + 1, max_backward_limit);
|
|
hasher->Store(ringbuffer + i, i + i_diff);
|
|
match_found = hasher->FindLongestMatch(
|
|
ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, average_cost,
|
|
dist_cache, i + i_diff + 1, max_length, max_distance,
|
|
&best_len_2, &best_len_code_2, &best_dist_2, &best_score_2);
|
|
double cost_diff_lazy = 7.0;
|
|
if (kUseCostModel) {
|
|
cost_diff_lazy = 0.0;
|
|
if (best_len >= 4) {
|
|
cost_diff_lazy +=
|
|
literal_cost[(i + 4) & literal_cost_mask] - average_cost;
|
|
}
|
|
{
|
|
const int tail_length = best_len_2 - best_len + 1;
|
|
for (int k = 0; k < tail_length; ++k) {
|
|
cost_diff_lazy -=
|
|
literal_cost[(i + best_len + k) & literal_cost_mask] -
|
|
average_cost;
|
|
}
|
|
}
|
|
// If we are not inserting any symbols, inserting one is more
|
|
// expensive than if we were inserting symbols anyways.
|
|
if (insert_length < 1) {
|
|
cost_diff_lazy += 0.97;
|
|
}
|
|
// Add bias to slightly avoid lazy matching.
|
|
cost_diff_lazy += 2.0 + delayed_backward_references_in_row * 0.2;
|
|
cost_diff_lazy += 0.04 * literal_cost[i & literal_cost_mask];
|
|
}
|
|
if (match_found && best_score_2 >= best_score + cost_diff_lazy) {
|
|
// Ok, let's just write one byte for now and start a match from the
|
|
// next byte.
|
|
++i;
|
|
++insert_length;
|
|
best_len = best_len_2;
|
|
best_len_code = best_len_code_2;
|
|
best_dist = best_dist_2;
|
|
best_score = best_score_2;
|
|
if (++delayed_backward_references_in_row < 4) {
|
|
continue;
|
|
}
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
apply_random_heuristics =
|
|
i + 2 * best_len + random_heuristics_window_size;
|
|
max_distance = std::min(i + i_diff, max_backward_limit);
|
|
int distance_code = best_dist + 16;
|
|
if (best_dist <= max_distance) {
|
|
if (best_dist == dist_cache[0]) {
|
|
distance_code = 1;
|
|
} else if (best_dist == dist_cache[1]) {
|
|
distance_code = 2;
|
|
} else if (best_dist == dist_cache[2]) {
|
|
distance_code = 3;
|
|
} else if (best_dist == dist_cache[3]) {
|
|
distance_code = 4;
|
|
} else if (quality > 1 && best_dist >= 6) {
|
|
for (int k = 4; k < kNumDistanceShortCodes; ++k) {
|
|
int idx = kDistanceCacheIndex[k];
|
|
int candidate = dist_cache[idx] + kDistanceCacheOffset[k];
|
|
static const int kLimits[16] = { 0, 0, 0, 0,
|
|
6, 6, 11, 11,
|
|
11, 11, 11, 11,
|
|
12, 12, 12, 12 };
|
|
if (best_dist == candidate && best_dist >= kLimits[k]) {
|
|
distance_code = k + 1;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
if (distance_code > 1) {
|
|
dist_cache[3] = dist_cache[2];
|
|
dist_cache[2] = dist_cache[1];
|
|
dist_cache[1] = dist_cache[0];
|
|
dist_cache[0] = best_dist;
|
|
}
|
|
}
|
|
Command cmd(insert_length, best_len, best_len_code, distance_code);
|
|
*commands++ = cmd;
|
|
*num_literals += insert_length;
|
|
insert_length = 0;
|
|
if (kUseDictionary) {
|
|
++i;
|
|
// Copy all copied literals to the hasher, except the last one.
|
|
// We cannot store the last one yet, otherwise we couldn't find
|
|
// the possible M1 match.
|
|
for (int j = 1; j < best_len - 1; ++j) {
|
|
if (i + 3 < i_end) {
|
|
hasher->Store(ringbuffer + i, i + i_diff);
|
|
}
|
|
++i;
|
|
}
|
|
// Prepare M1 match.
|
|
if (hasher->HasStaticDictionary() &&
|
|
best_len >= 4 && i + 20 < i_end && best_dist <= max_distance) {
|
|
max_distance = std::min(i + i_diff, max_backward_limit);
|
|
best_score_M1 = min_score;
|
|
match_found_M1 = hasher->FindLongestMatch(
|
|
ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, average_cost,
|
|
dist_cache, i + i_diff, i_end - i, max_distance,
|
|
&best_len_M1, &best_len_code_M1, &best_dist_M1, &best_score_M1);
|
|
} else {
|
|
match_found_M1 = false;
|
|
}
|
|
if (kUseCostModel) {
|
|
// This byte is just moved from the previous copy to the current,
|
|
// that is no gain.
|
|
best_score_M1 -= literal_cost[i & literal_cost_mask];
|
|
// Adjust for losing the opportunity for lazy matching.
|
|
best_score_M1 -= 3.75;
|
|
}
|
|
// Store the last one of the match.
|
|
if (i + 3 < i_end) {
|
|
hasher->Store(ringbuffer + i, i + i_diff);
|
|
}
|
|
++i;
|
|
} else {
|
|
// Put the hash keys into the table, if there are enough
|
|
// bytes left.
|
|
for (int j = 1; j < best_len; ++j) {
|
|
hasher->Store(&ringbuffer[i + j], i + i_diff + j);
|
|
}
|
|
i += best_len;
|
|
}
|
|
} else {
|
|
match_found_M1 = false;
|
|
++insert_length;
|
|
hasher->Store(ringbuffer + i, i + i_diff);
|
|
++i;
|
|
// If we have not seen matches for a long time, we can skip some
|
|
// match lookups. Unsuccessful match lookups are very very expensive
|
|
// and this kind of a heuristic speeds up compression quite
|
|
// a lot.
|
|
if (i > apply_random_heuristics) {
|
|
// Going through uncompressible data, jump.
|
|
if (i > apply_random_heuristics + 4 * random_heuristics_window_size) {
|
|
// It is quite a long time since we saw a copy, so we assume
|
|
// that this data is not compressible, and store hashes less
|
|
// often. Hashes of non compressible data are less likely to
|
|
// turn out to be useful in the future, too, so we store less of
|
|
// them to not to flood out the hash table of good compressible
|
|
// data.
|
|
int i_jump = std::min(i + 16, i_end - 4);
|
|
for (; i < i_jump; i += 4) {
|
|
hasher->Store(ringbuffer + i, i + i_diff);
|
|
insert_length += 4;
|
|
}
|
|
} else {
|
|
int i_jump = std::min(i + 8, i_end - 3);
|
|
for (; i < i_jump; i += 2) {
|
|
hasher->Store(ringbuffer + i, i + i_diff);
|
|
insert_length += 2;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
insert_length += (i_end - i);
|
|
*last_insert_len = insert_length;
|
|
*num_commands += (commands - orig_commands);
|
|
}
|
|
|
|
void CreateBackwardReferences(size_t num_bytes,
|
|
size_t position,
|
|
const uint8_t* ringbuffer,
|
|
size_t ringbuffer_mask,
|
|
const float* literal_cost,
|
|
size_t literal_cost_mask,
|
|
const size_t max_backward_limit,
|
|
const double base_min_score,
|
|
const int quality,
|
|
Hashers* hashers,
|
|
int hash_type,
|
|
int* dist_cache,
|
|
int* last_insert_len,
|
|
Command* commands,
|
|
int* num_commands,
|
|
int* num_literals) {
|
|
switch (hash_type) {
|
|
case 1:
|
|
CreateBackwardReferences<Hashers::H1, false, false>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h1.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
case 2:
|
|
CreateBackwardReferences<Hashers::H2, false, false>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h2.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
case 3:
|
|
CreateBackwardReferences<Hashers::H3, false, false>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h3.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
case 4:
|
|
CreateBackwardReferences<Hashers::H4, false, false>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h4.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
case 5:
|
|
CreateBackwardReferences<Hashers::H5, false, false>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h5.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
case 6:
|
|
CreateBackwardReferences<Hashers::H6, false, false>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h6.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
case 7:
|
|
CreateBackwardReferences<Hashers::H7, false, false>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h7.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
case 8:
|
|
CreateBackwardReferences<Hashers::H8, true, true>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h8.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
case 9:
|
|
CreateBackwardReferences<Hashers::H9, true, false>(
|
|
num_bytes, position, ringbuffer, ringbuffer_mask,
|
|
literal_cost, literal_cost_mask, max_backward_limit, base_min_score,
|
|
quality, hashers->hash_h9.get(), dist_cache, last_insert_len,
|
|
commands, num_commands, num_literals);
|
|
break;
|
|
default:
|
|
break;
|
|
}
|
|
}
|
|
|
|
} // namespace brotli
|