csrc/enc/encode.cc
// 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.
//
// Implementation of Brotli compressor.
#include "./encode.h"
#include <algorithm>
#include <limits>
#include "./backward_references.h"
#include "./bit_cost.h"
#include "./block_splitter.h"
#include "./brotli_bit_stream.h"
#include "./cluster.h"
#include "./context.h"
#include "./metablock.h"
#include "./transform.h"
#include "./entropy_encode.h"
#include "./fast_log.h"
#include "./hash.h"
#include "./histogram.h"
#include "./literal_cost.h"
#include "./prefix.h"
#include "./write_bits.h"
namespace brotli {
static const double kMinUTF8Ratio = 0.75;
int ParseAsUTF8(int* symbol, const uint8_t* input, int size) {
// ASCII
if ((input[0] & 0x80) == 0) {
*symbol = input[0];
if (*symbol > 0) {
return 1;
}
}
// 2-byte UTF8
if (size > 1 &&
(input[0] & 0xe0) == 0xc0 &&
(input[1] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x1f) << 6) |
(input[1] & 0x3f));
if (*symbol > 0x7f) {
return 2;
}
}
// 3-byte UFT8
if (size > 2 &&
(input[0] & 0xf0) == 0xe0 &&
(input[1] & 0xc0) == 0x80 &&
(input[2] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x0f) << 12) |
((input[1] & 0x3f) << 6) |
(input[2] & 0x3f));
if (*symbol > 0x7ff) {
return 3;
}
}
// 4-byte UFT8
if (size > 3 &&
(input[0] & 0xf8) == 0xf0 &&
(input[1] & 0xc0) == 0x80 &&
(input[2] & 0xc0) == 0x80 &&
(input[3] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x07) << 18) |
((input[1] & 0x3f) << 12) |
((input[2] & 0x3f) << 6) |
(input[3] & 0x3f));
if (*symbol > 0xffff && *symbol <= 0x10ffff) {
return 4;
}
}
// Not UTF8, emit a special symbol above the UTF8-code space
*symbol = 0x110000 | input[0];
return 1;
}
// Returns true if at least min_fraction of the data is UTF8-encoded.
bool IsMostlyUTF8(const uint8_t* data, size_t length, double min_fraction) {
size_t size_utf8 = 0;
size_t pos = 0;
while (pos < length) {
int symbol;
int bytes_read = ParseAsUTF8(&symbol, data + pos, length - pos);
pos += bytes_read;
if (symbol < 0x110000) size_utf8 += bytes_read;
}
return size_utf8 > min_fraction * length;
}
void RecomputeDistancePrefixes(Command* cmds,
size_t num_commands,
int num_direct_distance_codes,
int distance_postfix_bits) {
if (num_direct_distance_codes == 0 &&
distance_postfix_bits == 0) {
return;
}
for (int i = 0; i < num_commands; ++i) {
Command* cmd = &cmds[i];
if (cmd->copy_len_ > 0 && cmd->cmd_prefix_ >= 128) {
PrefixEncodeCopyDistance(cmd->DistanceCode(),
num_direct_distance_codes,
distance_postfix_bits,
&cmd->dist_prefix_,
&cmd->dist_extra_);
}
}
}
uint8_t* BrotliCompressor::GetBrotliStorage(size_t size) {
if (storage_size_ < size) {
storage_.reset(new uint8_t[size]);
storage_size_ = size;
}
return &storage_[0];
}
BrotliCompressor::BrotliCompressor(BrotliParams params)
: params_(params),
hashers_(new Hashers()),
input_pos_(0),
num_commands_(0),
last_insert_len_(0),
last_flush_pos_(0),
last_processed_pos_(0),
prev_byte_(0),
prev_byte2_(0),
storage_size_(0) {
// Sanitize params.
params_.quality = std::max(0, params_.quality);
if (params_.lgwin < kMinWindowBits) {
params_.lgwin = kMinWindowBits;
} else if (params_.lgwin > kMaxWindowBits) {
params_.lgwin = kMaxWindowBits;
}
if (params_.lgblock == 0) {
params_.lgblock = 16;
if (params_.quality >= 9 && params_.lgwin > params_.lgblock) {
params_.lgblock = std::min(21, params_.lgwin);
}
} else {
params_.lgblock = std::min(kMaxInputBlockBits,
std::max(kMinInputBlockBits, params_.lgblock));
}
if (params_.quality <= 9) {
params_.enable_dictionary = false;
params_.enable_transforms = false;
params_.greedy_block_split = true;
params_.enable_context_modeling = false;
}
// Set maximum distance, see section 9.1. of the spec.
max_backward_distance_ = (1 << params_.lgwin) - 16;
// Initialize input and literal cost ring buffers.
// We allocate at least lgwin + 1 bits for the ring buffer so that the newly
// added block fits there completely and we still get lgwin bits and at least
// read_block_size_bits + 1 bits because the copy tail length needs to be
// smaller than ringbuffer size.
int ringbuffer_bits = std::max(params_.lgwin + 1, params_.lgblock + 1);
ringbuffer_.reset(new RingBuffer(ringbuffer_bits, params_.lgblock));
if (params_.quality > 9) {
literal_cost_mask_ = (1 << params_.lgblock) - 1;
literal_cost_.reset(new float[literal_cost_mask_ + 1]);
}
// Allocate command buffer.
cmd_buffer_size_ = std::max(1 << 18, 1 << params_.lgblock);
commands_.reset(new brotli::Command[cmd_buffer_size_]);
// Initialize last byte with stream header.
if (params_.lgwin == 16) {
last_byte_ = 0;
last_byte_bits_ = 1;
} else {
last_byte_ = ((params_.lgwin - 17) << 1) | 1;
last_byte_bits_ = 4;
}
// Initialize distance cache.
dist_cache_[0] = 4;
dist_cache_[1] = 11;
dist_cache_[2] = 15;
dist_cache_[3] = 16;
// Initialize hashers.
switch (params_.quality) {
case 0:
case 1: hash_type_ = 1; break;
case 2:
case 3: hash_type_ = 2; break;
case 4: hash_type_ = 3; break;
case 5:
case 6: hash_type_ = 4; break;
case 7: hash_type_ = 5; break;
case 8: hash_type_ = 6; break;
case 9: hash_type_ = 7; break;
default: // quality > 9
hash_type_ = (params_.mode == BrotliParams::MODE_TEXT) ? 8 : 9;
}
hashers_->Init(hash_type_);
if (params_.mode == BrotliParams::MODE_TEXT &&
params_.enable_dictionary) {
StoreDictionaryWordHashes(params_.enable_transforms);
}
}
BrotliCompressor::~BrotliCompressor() {
}
StaticDictionary* BrotliCompressor::static_dictionary_ = NULL;
void BrotliCompressor::StoreDictionaryWordHashes(bool enable_transforms) {
if (static_dictionary_ == NULL) {
static_dictionary_ = new StaticDictionary;
static_dictionary_->Fill(enable_transforms);
}
hashers_->SetStaticDictionary(static_dictionary_);
}
void BrotliCompressor::CopyInputToRingBuffer(const size_t input_size,
const uint8_t* input_buffer) {
ringbuffer_->Write(input_buffer, input_size);
input_pos_ += input_size;
// Erase a few more bytes in the ring buffer to make hashing not
// depend on uninitialized data. This makes compression deterministic
// and it prevents uninitialized memory warnings in Valgrind. Even
// without erasing, the output would be valid (but nondeterministic).
//
// Background information: The compressor stores short (at most 8 bytes)
// substrings of the input already read in a hash table, and detects
// repetitions by looking up such substrings in the hash table. If it
// can find a substring, it checks whether the substring is really there
// in the ring buffer (or it's just a hash collision). Should the hash
// table become corrupt, this check makes sure that the output is
// still valid, albeit the compression ratio would be bad.
//
// The compressor populates the hash table from the ring buffer as it's
// reading new bytes from the input. However, at the last few indexes of
// the ring buffer, there are not enough bytes to build full-length
// substrings from. Since the hash table always contains full-length
// substrings, we erase with dummy 0s here to make sure that those
// substrings will contain 0s at the end instead of uninitialized
// data.
//
// Please note that erasing is not necessary (because the
// memory region is already initialized since he ring buffer
// has a `tail' that holds a copy of the beginning,) so we
// skip erasing if we have already gone around at least once in
// the ring buffer.
size_t pos = ringbuffer_->position();
// Only clear during the first round of ringbuffer writes. On
// subsequent rounds data in the ringbuffer would be affected.
if (pos <= ringbuffer_->mask()) {
// This is the first time when the ring buffer is being written.
// We clear 3 bytes just after the bytes that have been copied from
// the input buffer.
//
// The ringbuffer has a "tail" that holds a copy of the beginning,
// but only once the ring buffer has been fully written once, i.e.,
// pos <= mask. For the first time, we need to write values
// in this tail (where index may be larger than mask), so that
// we have exactly defined behavior and don't read un-initialized
// memory. Due to performance reasons, hashing reads data using a
// LOAD32, which can go 3 bytes beyond the bytes written in the
// ringbuffer.
memset(ringbuffer_->start() + pos, 0, 3);
}
}
bool BrotliCompressor::WriteBrotliData(const bool is_last,
const bool force_flush,
size_t* out_size,
uint8_t** output) {
const size_t bytes = input_pos_ - last_processed_pos_;
const uint8_t* data = ringbuffer_->start();
const size_t mask = ringbuffer_->mask();
if (bytes > input_block_size()) {
return false;
}
bool utf8_mode =
params_.enable_context_modeling &&
IsMostlyUTF8(&data[last_processed_pos_ & mask], bytes, kMinUTF8Ratio);
if (literal_cost_.get()) {
if (utf8_mode) {
EstimateBitCostsForLiteralsUTF8(last_processed_pos_, bytes, mask,
literal_cost_mask_, data,
literal_cost_.get());
} else {
EstimateBitCostsForLiterals(last_processed_pos_, bytes, mask,
literal_cost_mask_,
data, literal_cost_.get());
}
}
double base_min_score = params_.enable_context_modeling ? 8.115 : 4.0;
CreateBackwardReferences(bytes, last_processed_pos_, data, mask,
literal_cost_.get(),
literal_cost_mask_,
max_backward_distance_,
base_min_score,
params_.quality,
hashers_.get(),
hash_type_,
dist_cache_,
&last_insert_len_,
&commands_[num_commands_],
&num_commands_);
if (!is_last && !force_flush &&
num_commands_ + (input_block_size() >> 1) < cmd_buffer_size_ &&
input_pos_ + input_block_size() <= last_flush_pos_ + mask + 1) {
// Everything will happen later.
last_processed_pos_ = input_pos_;
*out_size = 0;
return true;
}
// Create the last insert-only command.
if (last_insert_len_ > 0) {
brotli::Command cmd(last_insert_len_);
commands_[num_commands_++] = cmd;
last_insert_len_ = 0;
}
return WriteMetaBlockInternal(is_last, utf8_mode, out_size, output);
}
bool BrotliCompressor::WriteMetaBlockInternal(const bool is_last,
const bool utf8_mode,
size_t* out_size,
uint8_t** output) {
const size_t bytes = input_pos_ - last_flush_pos_;
const uint8_t* data = ringbuffer_->start();
const size_t mask = ringbuffer_->mask();
const size_t max_out_size = 2 * bytes + 500;
uint8_t* storage = GetBrotliStorage(max_out_size);
storage[0] = last_byte_;
int storage_ix = last_byte_bits_;
bool uncompressed = false;
if (num_commands_ < (bytes >> 8) + 2) {
int num_literals = 0;
for (int i = 0; i < num_commands_; ++i) {
num_literals += commands_[i].insert_len_;
}
if (num_literals > 0.99 * bytes) {
int literal_histo[256] = { 0 };
static const int kSampleRate = 13;
static const double kMinEntropy = 7.92;
static const double kBitCostThreshold = bytes * kMinEntropy / kSampleRate;
for (int i = last_flush_pos_; i < input_pos_; i += kSampleRate) {
++literal_histo[data[i & mask]];
}
if (BitsEntropy(literal_histo, 256) > kBitCostThreshold) {
uncompressed = true;
}
}
}
if (bytes == 0) {
if (!StoreCompressedMetaBlockHeader(is_last, 0, &storage_ix, &storage[0])) {
return false;
}
storage_ix = (storage_ix + 7) & ~7;
} else if (uncompressed) {
if (!StoreUncompressedMetaBlock(is_last,
data, last_flush_pos_, mask, bytes,
&storage_ix,
&storage[0])) {
return false;
}
} else {
// Save the state of the distance cache in case we need to restore it for
// emitting an uncompressed block.
int saved_dist_cache[4];
memcpy(saved_dist_cache, dist_cache_, sizeof(dist_cache_));
int num_direct_distance_codes = 0;
int distance_postfix_bits = 0;
if (params_.quality > 9 && params_.mode == BrotliParams::MODE_FONT) {
num_direct_distance_codes = 12;
distance_postfix_bits = 1;
RecomputeDistancePrefixes(commands_.get(),
num_commands_,
num_direct_distance_codes,
distance_postfix_bits);
}
int literal_context_mode = utf8_mode ? CONTEXT_UTF8 : CONTEXT_SIGNED;
MetaBlockSplit mb;
if (params_.greedy_block_split) {
BuildMetaBlockGreedy(data, last_flush_pos_, mask,
commands_.get(), num_commands_,
&mb);
} else {
BuildMetaBlock(data, last_flush_pos_, mask,
prev_byte_, prev_byte2_,
commands_.get(), num_commands_,
literal_context_mode,
params_.enable_context_modeling,
&mb);
}
if (params_.quality >= 3) {
OptimizeHistograms(num_direct_distance_codes,
distance_postfix_bits,
&mb);
}
if (!StoreMetaBlock(data, last_flush_pos_, bytes, mask,
prev_byte_, prev_byte2_,
is_last,
num_direct_distance_codes,
distance_postfix_bits,
literal_context_mode,
commands_.get(), num_commands_,
mb,
&storage_ix,
&storage[0])) {
return false;
}
if (bytes + 4 < (storage_ix >> 3)) {
// Restore the distance cache and last byte.
memcpy(dist_cache_, saved_dist_cache, sizeof(dist_cache_));
storage[0] = last_byte_;
storage_ix = last_byte_bits_;
if (!StoreUncompressedMetaBlock(is_last, data, last_flush_pos_, mask,
bytes, &storage_ix, &storage[0])) {
return false;
}
}
}
last_byte_ = storage[storage_ix >> 3];
last_byte_bits_ = storage_ix & 7;
last_flush_pos_ = input_pos_;
last_processed_pos_ = input_pos_;
prev_byte_ = data[(last_flush_pos_ - 1) & mask];
prev_byte2_ = data[(last_flush_pos_ - 2) & mask];
num_commands_ = 0;
*output = &storage[0];
*out_size = storage_ix >> 3;
return true;
}
bool BrotliCompressor::WriteMetaBlock(const size_t input_size,
const uint8_t* input_buffer,
const bool is_last,
size_t* encoded_size,
uint8_t* encoded_buffer) {
CopyInputToRingBuffer(input_size, input_buffer);
size_t out_size = 0;
uint8_t* output;
if (!WriteBrotliData(is_last, /* force_flush = */ true, &out_size, &output) ||
out_size > *encoded_size) {
return false;
}
if (out_size > 0) {
memcpy(encoded_buffer, output, out_size);
}
*encoded_size = out_size;
return true;
}
bool BrotliCompressor::WriteMetadata(const size_t input_size,
const uint8_t* input_buffer,
const bool is_last,
size_t* encoded_size,
uint8_t* encoded_buffer) {
if (input_size > (1 << 24) || input_size + 6 > *encoded_size) {
return false;
}
int storage_ix = last_byte_bits_;
encoded_buffer[0] = last_byte_;
WriteBits(1, 0, &storage_ix, encoded_buffer);
WriteBits(2, 3, &storage_ix, encoded_buffer);
WriteBits(1, 0, &storage_ix, encoded_buffer);
if (input_size == 0) {
WriteBits(2, 0, &storage_ix, encoded_buffer);
*encoded_size = (storage_ix + 7) >> 3;
} else {
size_t nbits = Log2Floor(input_size - 1) + 1;
size_t nbytes = (nbits + 7) / 8;
WriteBits(2, nbytes, &storage_ix, encoded_buffer);
WriteBits(8 * nbytes, input_size - 1, &storage_ix, encoded_buffer);
size_t hdr_size = (storage_ix + 7) >> 3;
memcpy(&encoded_buffer[hdr_size], input_buffer, input_size);
*encoded_size = hdr_size + input_size;
}
if (is_last) {
encoded_buffer[(*encoded_size)++] = 3;
}
last_byte_ = 0;
last_byte_bits_ = 0;
return true;
}
bool BrotliCompressor::FinishStream(
size_t* encoded_size, uint8_t* encoded_buffer) {
return WriteMetaBlock(0, NULL, true, encoded_size, encoded_buffer);
}
int BrotliCompressBuffer(BrotliParams params,
size_t input_size,
const uint8_t* input_buffer,
size_t* encoded_size,
uint8_t* encoded_buffer) {
if (*encoded_size == 0) {
// Output buffer needs at least one byte.
return 0;
}
BrotliCompressor compressor(params);
BrotliMemIn in(input_buffer, input_size);
BrotliMemOut out(encoded_buffer, *encoded_size);
if (!BrotliCompress(params, &in, &out)) {
return 0;
}
*encoded_size = out.position();
return 1;
}
size_t CopyOneBlockToRingBuffer(BrotliIn* r, BrotliCompressor* compressor) {
const size_t block_size = compressor->input_block_size();
size_t bytes_read = 0;
const uint8_t* data = reinterpret_cast<const uint8_t*>(
r->Read(block_size, &bytes_read));
if (data == NULL) {
return 0;
}
compressor->CopyInputToRingBuffer(bytes_read, data);
// Read more bytes until block_size is filled or an EOF (data == NULL) is
// received. This is useful to get deterministic compressed output for the
// same input no matter how r->Read splits the input to chunks.
for (size_t remaining = block_size - bytes_read; remaining > 0; ) {
size_t more_bytes_read = 0;
data = reinterpret_cast<const uint8_t*>(
r->Read(remaining, &more_bytes_read));
if (data == NULL) {
break;
}
compressor->CopyInputToRingBuffer(more_bytes_read, data);
bytes_read += more_bytes_read;
remaining -= more_bytes_read;
}
return bytes_read;
}
bool BrotliInIsFinished(BrotliIn* r) {
size_t read_bytes;
return r->Read(0, &read_bytes) == NULL;
}
int BrotliCompress(BrotliParams params, BrotliIn* in, BrotliOut* out) {
size_t in_bytes = 0;
size_t out_bytes = 0;
uint8_t* output;
bool final_block = false;
BrotliCompressor compressor(params);
while (!final_block) {
in_bytes = CopyOneBlockToRingBuffer(in, &compressor);
final_block = in_bytes == 0 || BrotliInIsFinished(in);
out_bytes = 0;
if (!compressor.WriteBrotliData(final_block,
/* force_flush = */ false,
&out_bytes, &output)) {
return false;
}
if (out_bytes > 0 && !out->Write(output, out_bytes)) {
return false;
}
}
return true;
}
} // namespace brotli