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028291865d
brotli/enc/encode.cc
Eugene Kliuchnikov 028291865d Extract common parts: constants, dictionary, etc.
2016-06-03 10:51:04 +02:00

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/* Copyright 2013 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
// Implementation of Brotli compressor.
#include "./encode.h"
#include <algorithm>
#include <cstdlib> /* free, malloc */
#include <cstring> /* memset */
#include <limits>
#include "./backward_references.h"
#include "./bit_cost.h"
#include "./block_splitter.h"
#include "./brotli_bit_stream.h"
#include "./cluster.h"
#include "./compress_fragment.h"
#include "./compress_fragment_two_pass.h"
#include "./context.h"
#include "./entropy_encode.h"
#include "./fast_log.h"
#include "./hash.h"
#include "./histogram.h"
#include "./metablock.h"
#include "./prefix.h"
#include "./transform.h"
#include "./utf8_util.h"
#include "./write_bits.h"
namespace brotli {
static const int kMinQualityForBlockSplit = 4;
static const int kMinQualityForContextModeling = 5;
static const int kMinQualityForOptimizeHistograms = 4;
// For quality 2 there is no block splitting, so we buffer at most this much
// literals and commands.
static const size_t kMaxNumDelayedSymbols = 0x2fff;
#define COPY_ARRAY(dst, src) memcpy(dst, src, sizeof(src));
static void RecomputeDistancePrefixes(Command* cmds,
size_t num_commands,
uint32_t num_direct_distance_codes,
uint32_t distance_postfix_bits) {
if (num_direct_distance_codes == 0 && distance_postfix_bits == 0) {
return;
}
for (size_t i = 0; i < num_commands; ++i) {
Command* cmd = &cmds[i];
if (cmd->copy_len() && cmd->cmd_prefix_ >= 128) {
PrefixEncodeCopyDistance(cmd->DistanceCode(),
num_direct_distance_codes,
distance_postfix_bits,
&cmd->dist_prefix_,
&cmd->dist_extra_);
}
}
}
/* Wraps 64-bit input position to 32-bit ringbuffer position preserving
"not-a-first-lap" feature. */
static uint32_t WrapPosition(uint64_t position) {
uint32_t result = static_cast<uint32_t>(position);
if (position > (1u << 30)) {
result = (result & ((1u << 30) - 1)) | (1u << 30);
}
return result;
}
uint8_t* BrotliCompressor::GetBrotliStorage(size_t size) {
if (storage_size_ < size) {
delete[] storage_;
storage_ = new uint8_t[size];
storage_size_ = size;
}
return storage_;
}
static size_t MaxHashTableSize(int quality) {
return quality == 0 ? 1 << 15 : 1 << 17;
}
static size_t HashTableSize(size_t max_table_size, size_t input_size) {
size_t htsize = 256;
while (htsize < max_table_size && htsize < input_size) {
htsize <<= 1;
}
return htsize;
}
int* BrotliCompressor::GetHashTable(int quality,
size_t input_size,
size_t* table_size) {
// Use smaller hash table when input.size() is smaller, since we
// fill the table, incurring O(hash table size) overhead for
// compression, and if the input is short, we won't need that
// many hash table entries anyway.
const size_t max_table_size = MaxHashTableSize(quality);
assert(max_table_size >= 256);
size_t htsize = HashTableSize(max_table_size, input_size);
int* table;
if (htsize <= sizeof(small_table_) / sizeof(small_table_[0])) {
table = small_table_;
} else {
if (large_table_ == NULL) {
large_table_ = new int[max_table_size];
}
table = large_table_;
}
*table_size = htsize;
memset(table, 0, htsize * sizeof(*table));
return table;
}
static void EncodeWindowBits(int lgwin, uint8_t* last_byte,
uint8_t* last_byte_bits) {
if (lgwin == 16) {
*last_byte = 0;
*last_byte_bits = 1;
} else if (lgwin == 17) {
*last_byte = 1;
*last_byte_bits = 7;
} else if (lgwin > 17) {
*last_byte = static_cast<uint8_t>(((lgwin - 17) << 1) | 1);
*last_byte_bits = 4;
} else {
*last_byte = static_cast<uint8_t>(((lgwin - 8) << 4) | 1);
*last_byte_bits = 7;
}
}
// Initializes the command and distance prefix codes for the first block.
static void InitCommandPrefixCodes(uint8_t cmd_depths[128],
uint16_t cmd_bits[128],
uint8_t cmd_code[512],
size_t* cmd_code_numbits) {
static const uint8_t kDefaultCommandDepths[128] = {
0, 4, 4, 5, 6, 6, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8,
0, 0, 0, 4, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7,
7, 7, 10, 10, 10, 10, 10, 10, 0, 4, 4, 5, 5, 5, 6, 6,
7, 8, 8, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
6, 6, 6, 6, 6, 6, 5, 5, 5, 5, 5, 5, 4, 4, 4, 4,
4, 4, 4, 5, 5, 5, 5, 5, 5, 6, 6, 7, 7, 7, 8, 10,
12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
};
static const uint16_t kDefaultCommandBits[128] = {
0, 0, 8, 9, 3, 35, 7, 71,
39, 103, 23, 47, 175, 111, 239, 31,
0, 0, 0, 4, 12, 2, 10, 6,
13, 29, 11, 43, 27, 59, 87, 55,
15, 79, 319, 831, 191, 703, 447, 959,
0, 14, 1, 25, 5, 21, 19, 51,
119, 159, 95, 223, 479, 991, 63, 575,
127, 639, 383, 895, 255, 767, 511, 1023,
14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
27, 59, 7, 39, 23, 55, 30, 1, 17, 9, 25, 5, 0, 8, 4, 12,
2, 10, 6, 21, 13, 29, 3, 19, 11, 15, 47, 31, 95, 63, 127, 255,
767, 2815, 1791, 3839, 511, 2559, 1535, 3583, 1023, 3071, 2047, 4095,
};
COPY_ARRAY(cmd_depths, kDefaultCommandDepths);
COPY_ARRAY(cmd_bits, kDefaultCommandBits);
// Initialize the pre-compressed form of the command and distance prefix
// codes.
static const uint8_t kDefaultCommandCode[] = {
0xff, 0x77, 0xd5, 0xbf, 0xe7, 0xde, 0xea, 0x9e, 0x51, 0x5d, 0xde, 0xc6,
0x70, 0x57, 0xbc, 0x58, 0x58, 0x58, 0xd8, 0xd8, 0x58, 0xd5, 0xcb, 0x8c,
0xea, 0xe0, 0xc3, 0x87, 0x1f, 0x83, 0xc1, 0x60, 0x1c, 0x67, 0xb2, 0xaa,
0x06, 0x83, 0xc1, 0x60, 0x30, 0x18, 0xcc, 0xa1, 0xce, 0x88, 0x54, 0x94,
0x46, 0xe1, 0xb0, 0xd0, 0x4e, 0xb2, 0xf7, 0x04, 0x00,
};
static const int kDefaultCommandCodeNumBits = 448;
COPY_ARRAY(cmd_code, kDefaultCommandCode);
*cmd_code_numbits = kDefaultCommandCodeNumBits;
}
// Decide about the context map based on the ability of the prediction
// ability of the previous byte UTF8-prefix on the next byte. The
// prediction ability is calculated as shannon entropy. Here we need
// shannon entropy instead of 'BitsEntropy' since the prefix will be
// encoded with the remaining 6 bits of the following byte, and
// BitsEntropy will assume that symbol to be stored alone using Huffman
// coding.
static void ChooseContextMap(int quality,
uint32_t* bigram_histo,
size_t* num_literal_contexts,
const uint32_t** literal_context_map) {
uint32_t monogram_histo[3] = { 0 };
uint32_t two_prefix_histo[6] = { 0 };
size_t total = 0;
for (size_t i = 0; i < 9; ++i) {
total += bigram_histo[i];
monogram_histo[i % 3] += bigram_histo[i];
size_t j = i;
if (j >= 6) {
j -= 6;
}
two_prefix_histo[j] += bigram_histo[i];
}
size_t dummy;
double entropy1 = ShannonEntropy(monogram_histo, 3, &dummy);
double entropy2 = (ShannonEntropy(two_prefix_histo, 3, &dummy) +
ShannonEntropy(two_prefix_histo + 3, 3, &dummy));
double entropy3 = 0;
for (size_t k = 0; k < 3; ++k) {
entropy3 += ShannonEntropy(bigram_histo + 3 * k, 3, &dummy);
}
assert(total != 0);
double scale = 1.0 / static_cast<double>(total);
entropy1 *= scale;
entropy2 *= scale;
entropy3 *= scale;
static const uint32_t kStaticContextMapContinuation[64] = {
1, 1, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
};
static const uint32_t kStaticContextMapSimpleUTF8[64] = {
0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
};
if (quality < 7) {
// 3 context models is a bit slower, don't use it at lower qualities.
entropy3 = entropy1 * 10;
}
// If expected savings by symbol are less than 0.2 bits, skip the
// context modeling -- in exchange for faster decoding speed.
if (entropy1 - entropy2 < 0.2 &&
entropy1 - entropy3 < 0.2) {
*num_literal_contexts = 1;
} else if (entropy2 - entropy3 < 0.02) {
*num_literal_contexts = 2;
*literal_context_map = kStaticContextMapSimpleUTF8;
} else {
*num_literal_contexts = 3;
*literal_context_map = kStaticContextMapContinuation;
}
}
static void DecideOverLiteralContextModeling(
const uint8_t* input,
size_t start_pos,
size_t length,
size_t mask,
int quality,
ContextType* literal_context_mode,
size_t* num_literal_contexts,
const uint32_t** literal_context_map) {
if (quality < kMinQualityForContextModeling || length < 64) {
return;
}
// Gather bigram data of the UTF8 byte prefixes. To make the analysis of
// UTF8 data faster we only examine 64 byte long strides at every 4kB
// intervals.
const size_t end_pos = start_pos + length;
uint32_t bigram_prefix_histo[9] = { 0 };
for (; start_pos + 64 <= end_pos; start_pos += 4096) {
static const int lut[4] = { 0, 0, 1, 2 };
const size_t stride_end_pos = start_pos + 64;
int prev = lut[input[start_pos & mask] >> 6] * 3;
for (size_t pos = start_pos + 1; pos < stride_end_pos; ++pos) {
const uint8_t literal = input[pos & mask];
++bigram_prefix_histo[prev + lut[literal >> 6]];
prev = lut[literal >> 6] * 3;
}
}
*literal_context_mode = CONTEXT_UTF8;
ChooseContextMap(quality, &bigram_prefix_histo[0], num_literal_contexts,
literal_context_map);
}
static bool ShouldCompress(const uint8_t* data,
const size_t mask,
const uint64_t last_flush_pos,
const size_t bytes,
const size_t num_literals,
const size_t num_commands) {
if (num_commands < (bytes >> 8) + 2) {
if (num_literals > 0.99 * static_cast<double>(bytes)) {
uint32_t literal_histo[256] = { 0 };
static const uint32_t kSampleRate = 13;
static const double kMinEntropy = 7.92;
const double bit_cost_threshold =
static_cast<double>(bytes) * kMinEntropy / kSampleRate;
size_t t = (bytes + kSampleRate - 1) / kSampleRate;
uint32_t pos = static_cast<uint32_t>(last_flush_pos);
for (size_t i = 0; i < t; i++) {
++literal_histo[data[pos & mask]];
pos += kSampleRate;
}
if (BitsEntropy(literal_histo, 256) > bit_cost_threshold) {
return false;
}
}
}
return true;
}
static void WriteMetaBlockInternal(const uint8_t* data,
const size_t mask,
const uint64_t last_flush_pos,
const size_t bytes,
const bool is_last,
const int quality,
const bool font_mode,
const uint8_t prev_byte,
const uint8_t prev_byte2,
const size_t num_literals,
const size_t num_commands,
Command* commands,
const int* saved_dist_cache,
int* dist_cache,
size_t* storage_ix,
uint8_t* storage) {
if (bytes == 0) {
// Write the ISLAST and ISEMPTY bits.
WriteBits(2, 3, storage_ix, storage);
*storage_ix = (*storage_ix + 7u) & ~7u;
return;
}
if (!ShouldCompress(data, mask, last_flush_pos, bytes,
num_literals, num_commands)) {
// Restore the distance cache, as its last update by
// CreateBackwardReferences is now unused.
memcpy(dist_cache, saved_dist_cache, 4 * sizeof(dist_cache[0]));
StoreUncompressedMetaBlock(is_last, data,
WrapPosition(last_flush_pos), mask, bytes,
storage_ix, storage);
return;
}
const uint8_t last_byte = storage[0];
const uint8_t last_byte_bits = static_cast<uint8_t>(*storage_ix & 0xff);
uint32_t num_direct_distance_codes = 0;
uint32_t distance_postfix_bits = 0;
if (quality > 9 && font_mode) {
num_direct_distance_codes = 12;
distance_postfix_bits = 1;
RecomputeDistancePrefixes(commands,
num_commands,
num_direct_distance_codes,
distance_postfix_bits);
}
if (quality == 2) {
StoreMetaBlockFast(data, WrapPosition(last_flush_pos),
bytes, mask, is_last,
commands, num_commands,
storage_ix, storage);
} else if (quality < kMinQualityForBlockSplit) {
StoreMetaBlockTrivial(data, WrapPosition(last_flush_pos),
bytes, mask, is_last,
commands, num_commands,
storage_ix, storage);
} else {
MetaBlockSplit mb;
ContextType literal_context_mode = CONTEXT_UTF8;
if (quality <= 9) {
size_t num_literal_contexts = 1;
const uint32_t* literal_context_map = NULL;
DecideOverLiteralContextModeling(data, WrapPosition(last_flush_pos),
bytes, mask,
quality,
&literal_context_mode,
&num_literal_contexts,
&literal_context_map);
if (literal_context_map == NULL) {
BuildMetaBlockGreedy(data, WrapPosition(last_flush_pos), mask,
commands, num_commands, &mb);
} else {
BuildMetaBlockGreedyWithContexts(data, WrapPosition(last_flush_pos),
mask,
prev_byte, prev_byte2,
literal_context_mode,
num_literal_contexts,
literal_context_map,
commands, num_commands,
&mb);
}
} else {
if (!IsMostlyUTF8(data, WrapPosition(last_flush_pos), mask, bytes,
kMinUTF8Ratio)) {
literal_context_mode = CONTEXT_SIGNED;
}
BuildMetaBlock(data, WrapPosition(last_flush_pos), mask,
prev_byte, prev_byte2,
commands, num_commands,
literal_context_mode,
&mb);
}
if (quality >= kMinQualityForOptimizeHistograms) {
OptimizeHistograms(num_direct_distance_codes,
distance_postfix_bits,
&mb);
}
StoreMetaBlock(data, WrapPosition(last_flush_pos), bytes, mask,
prev_byte, prev_byte2,
is_last,
num_direct_distance_codes,
distance_postfix_bits,
literal_context_mode,
commands, num_commands,
mb,
storage_ix, storage);
}
if (bytes + 4 < (*storage_ix >> 3)) {
// Restore the distance cache and last byte.
memcpy(dist_cache, saved_dist_cache, 4 * sizeof(dist_cache[0]));
storage[0] = last_byte;
*storage_ix = last_byte_bits;
StoreUncompressedMetaBlock(is_last, data,
WrapPosition(last_flush_pos), mask,
bytes, storage_ix, storage);
}
}
BrotliCompressor::BrotliCompressor(BrotliParams params)
: params_(params),
hashers_(new Hashers()),
input_pos_(0),
num_commands_(0),
num_literals_(0),
last_insert_len_(0),
last_flush_pos_(0),
last_processed_pos_(0),
prev_byte_(0),
prev_byte2_(0),
storage_size_(0),
storage_(0),
large_table_(NULL),
cmd_code_numbits_(0),
command_buf_(NULL),
literal_buf_(NULL),
is_last_block_emitted_(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_.quality <= 1) {
params_.lgblock = params_.lgwin;
} else if (params_.quality < kMinQualityForBlockSplit) {
params_.lgblock = 14;
} else if (params_.lgblock == 0) {
params_.lgblock = 16;
if (params_.quality >= 9 && params_.lgwin > params_.lgblock) {
params_.lgblock = std::min(18, params_.lgwin);
}
} else {
params_.lgblock = std::min(kMaxInputBlockBits,
std::max(kMinInputBlockBits, params_.lgblock));
}
// 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_ = new RingBuffer(ringbuffer_bits, params_.lgblock);
commands_ = 0;
cmd_alloc_size_ = 0;
// Initialize last byte with stream header.
EncodeWindowBits(params_.lgwin, &last_byte_, &last_byte_bits_);
// Initialize distance cache.
dist_cache_[0] = 4;
dist_cache_[1] = 11;
dist_cache_[2] = 15;
dist_cache_[3] = 16;
// Save the state of the distance cache in case we need to restore it for
// emitting an uncompressed block.
memcpy(saved_dist_cache_, dist_cache_, sizeof(dist_cache_));
if (params_.quality == 0) {
InitCommandPrefixCodes(cmd_depths_, cmd_bits_,
cmd_code_, &cmd_code_numbits_);
} else if (params_.quality == 1) {
command_buf_ = new uint32_t[kCompressFragmentTwoPassBlockSize];
literal_buf_ = new uint8_t[kCompressFragmentTwoPassBlockSize];
}
// Initialize hashers.
hash_type_ = std::min(10, params_.quality);
hashers_->Init(hash_type_);
}
BrotliCompressor::~BrotliCompressor(void) {
delete[] storage_;
free(commands_);
delete ringbuffer_;
delete hashers_;
delete[] large_table_;
delete[] command_buf_;
delete[] literal_buf_;
}
void BrotliCompressor::CopyInputToRingBuffer(const size_t input_size,
const uint8_t* input_buffer) {
ringbuffer_->Write(input_buffer, input_size);
input_pos_ += input_size;
// TL;DR: If needed, initialize 7 more bytes in the ring buffer to make the
// 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 7 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
// LOAD64, which can go 7 bytes beyond the bytes written in the
// ringbuffer.
memset(ringbuffer_->start() + pos, 0, 7);
}
}
void BrotliCompressor::BrotliSetCustomDictionary(
const size_t size, const uint8_t* dict) {
CopyInputToRingBuffer(size, dict);
last_flush_pos_ = size;
last_processed_pos_ = size;
if (size > 0) {
prev_byte_ = dict[size - 1];
}
if (size > 1) {
prev_byte2_ = dict[size - 2];
}
hashers_->PrependCustomDictionary(hash_type_, params_.lgwin, size, dict);
}
bool BrotliCompressor::WriteBrotliData(const bool is_last,
const bool force_flush,
size_t* out_size,
uint8_t** output) {
const uint64_t delta = input_pos_ - last_processed_pos_;
const uint8_t* data = ringbuffer_->start();
const uint32_t mask = ringbuffer_->mask();
/* Adding more blocks after "last" block is forbidden. */
if (is_last_block_emitted_) return false;
if (is_last) is_last_block_emitted_ = 1;
if (delta > input_block_size()) {
return false;
}
const uint32_t bytes = static_cast<uint32_t>(delta);
if (params_.quality <= 1) {
if (delta == 0 && !is_last) {
// We have no new input data and we don't have to finish the stream, so
// nothing to do.
*out_size = 0;
return true;
}
const size_t max_out_size = 2 * bytes + 500;
uint8_t* storage = GetBrotliStorage(max_out_size);
storage[0] = last_byte_;
size_t storage_ix = last_byte_bits_;
size_t table_size;
int* table = GetHashTable(params_.quality, bytes, &table_size);
if (params_.quality == 0) {
BrotliCompressFragmentFast(
&data[WrapPosition(last_processed_pos_) & mask],
bytes, is_last,
table, table_size,
cmd_depths_, cmd_bits_,
&cmd_code_numbits_, cmd_code_,
&storage_ix, storage);
} else {
BrotliCompressFragmentTwoPass(
&data[WrapPosition(last_processed_pos_) & mask],
bytes, is_last,
command_buf_, literal_buf_,
table, table_size,
&storage_ix, storage);
}
last_byte_ = storage[storage_ix >> 3];
last_byte_bits_ = storage_ix & 7u;
last_processed_pos_ = input_pos_;
*output = &storage[0];
*out_size = storage_ix >> 3;
return true;
}
// Theoretical max number of commands is 1 per 2 bytes.
size_t newsize = num_commands_ + bytes / 2 + 1;
if (newsize > cmd_alloc_size_) {
// Reserve a bit more memory to allow merging with a next block
// without realloc: that would impact speed.
newsize += (bytes / 4) + 16;
cmd_alloc_size_ = newsize;
commands_ =
static_cast<Command*>(realloc(commands_, sizeof(Command) * newsize));
}
CreateBackwardReferences(bytes, WrapPosition(last_processed_pos_),
is_last, data, mask,
params_.quality,
params_.lgwin,
hashers_,
hash_type_,
dist_cache_,
&last_insert_len_,
&commands_[num_commands_],
&num_commands_,
&num_literals_);
size_t max_length = std::min<size_t>(mask + 1, 1u << kMaxInputBlockBits);
const size_t max_literals = max_length / 8;
const size_t max_commands = max_length / 8;
if (!is_last && !force_flush &&
(params_.quality >= kMinQualityForBlockSplit ||
(num_literals_ + num_commands_ < kMaxNumDelayedSymbols)) &&
num_literals_ < max_literals &&
num_commands_ < max_commands &&
input_pos_ + input_block_size() <= last_flush_pos_ + max_length) {
// Merge with next input block. 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;
num_literals_ += last_insert_len_;
last_insert_len_ = 0;
}
if (!is_last && input_pos_ == last_flush_pos_) {
// We have no new input data and we don't have to finish the stream, so
// nothing to do.
*out_size = 0;
return true;
}
assert(input_pos_ >= last_flush_pos_);
assert(input_pos_ > last_flush_pos_ || is_last);
assert(input_pos_ - last_flush_pos_ <= 1u << 24);
const uint32_t metablock_size =
static_cast<uint32_t>(input_pos_ - last_flush_pos_);
const size_t max_out_size = 2 * metablock_size + 500;
uint8_t* storage = GetBrotliStorage(max_out_size);
storage[0] = last_byte_;
size_t storage_ix = last_byte_bits_;
bool font_mode = params_.mode == BrotliParams::MODE_FONT;
WriteMetaBlockInternal(
data, mask, last_flush_pos_, metablock_size, is_last, params_.quality,
font_mode, prev_byte_, prev_byte2_, num_literals_, num_commands_,
commands_, saved_dist_cache_, dist_cache_, &storage_ix, storage);
last_byte_ = storage[storage_ix >> 3];
last_byte_bits_ = storage_ix & 7u;
last_flush_pos_ = input_pos_;
last_processed_pos_ = input_pos_;
if (last_flush_pos_ > 0) {
prev_byte_ = data[(static_cast<uint32_t>(last_flush_pos_) - 1) & mask];
}
if (last_flush_pos_ > 1) {
prev_byte2_ = data[(static_cast<uint32_t>(last_flush_pos_) - 2) & mask];
}
num_commands_ = 0;
num_literals_ = 0;
// Save the state of the distance cache in case we need to restore it for
// emitting an uncompressed block.
memcpy(saved_dist_cache_, dist_cache_, sizeof(dist_cache_));
*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;
}
uint64_t hdr_buffer_data[2];
uint8_t* hdr_buffer = reinterpret_cast<uint8_t*>(&hdr_buffer_data[0]);
size_t storage_ix = last_byte_bits_;
hdr_buffer[0] = last_byte_;
WriteBits(1, 0, &storage_ix, hdr_buffer);
WriteBits(2, 3, &storage_ix, hdr_buffer);
WriteBits(1, 0, &storage_ix, hdr_buffer);
if (input_size == 0) {
WriteBits(2, 0, &storage_ix, hdr_buffer);
*encoded_size = (storage_ix + 7u) >> 3;
memcpy(encoded_buffer, hdr_buffer, *encoded_size);
} else {
uint32_t nbits = (input_size == 1) ? 0 : (Log2FloorNonZero(
static_cast<uint32_t>(input_size) - 1) + 1);
uint32_t nbytes = (nbits + 7) / 8;
WriteBits(2, nbytes, &storage_ix, hdr_buffer);
WriteBits(8 * nbytes, input_size - 1, &storage_ix, hdr_buffer);
size_t hdr_size = (storage_ix + 7u) >> 3;
memcpy(encoded_buffer, hdr_buffer, hdr_size);
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);
}
static int BrotliCompressBufferQuality10(int lgwin,
size_t input_size,
const uint8_t* input_buffer,
size_t* encoded_size,
uint8_t* encoded_buffer) {
const size_t mask = std::numeric_limits<size_t>::max() >> 1;
assert(input_size <= mask + 1);
const size_t max_backward_limit = (1 << lgwin) - 16;
int dist_cache[4] = { 4, 11, 15, 16 };
int saved_dist_cache[4] = { 4, 11, 15, 16 };
int ok = 1;
const size_t max_out_size = *encoded_size;
size_t total_out_size = 0;
uint8_t last_byte;
uint8_t last_byte_bits;
EncodeWindowBits(lgwin, &last_byte, &last_byte_bits);
Hashers::H10* hasher = new Hashers::H10;
const size_t hasher_eff_size = std::min(input_size, max_backward_limit + 16);
hasher->Init(lgwin, 0, hasher_eff_size, true);
const int lgblock = std::min(18, lgwin);
const int lgmetablock = std::min(24, lgwin + 1);
const size_t max_block_size = static_cast<size_t>(1) << lgblock;
const size_t max_metablock_size = static_cast<size_t>(1) << lgmetablock;
const size_t max_literals_per_metablock = max_metablock_size / 8;
const size_t max_commands_per_metablock = max_metablock_size / 8;
size_t metablock_start = 0;
uint8_t prev_byte = 0;
uint8_t prev_byte2 = 0;
while (ok && metablock_start < input_size) {
const size_t metablock_end =
std::min(input_size, metablock_start + max_metablock_size);
const size_t expected_num_commands =
(metablock_end - metablock_start) / 12 + 16;
Command* commands = 0;
size_t num_commands = 0;
size_t last_insert_len = 0;
size_t num_literals = 0;
size_t metablock_size = 0;
size_t cmd_alloc_size = 0;
for (size_t block_start = metablock_start; block_start < metablock_end; ) {
size_t block_size = std::min(metablock_end - block_start, max_block_size);
ZopfliNode* nodes = new ZopfliNode[block_size + 1];
std::vector<uint32_t> path;
hasher->StitchToPreviousBlock(block_size, block_start,
input_buffer, mask);
ZopfliComputeShortestPath(block_size, block_start, input_buffer, mask,
max_backward_limit, dist_cache,
hasher, nodes, &path);
// We allocate a command buffer in the first iteration of this loop that
// will be likely big enough for the whole metablock, so that for most
// inputs we will not have to reallocate in later iterations. We do the
// allocation here and not before the loop, because if the input is small,
// this will be allocated after the zopfli cost model is freed, so this
// will not increase peak memory usage.
// TODO: If the first allocation is too small, increase command
// buffer size exponentially.
size_t new_cmd_alloc_size = std::max(expected_num_commands,
num_commands + path.size() + 1);
if (cmd_alloc_size != new_cmd_alloc_size) {
cmd_alloc_size = new_cmd_alloc_size;
commands = static_cast<Command*>(
realloc(commands, cmd_alloc_size * sizeof(Command)));
}
ZopfliCreateCommands(block_size, block_start, max_backward_limit, path,
&nodes[0], dist_cache, &last_insert_len,
&commands[num_commands], &num_literals);
num_commands += path.size();
block_start += block_size;
metablock_size += block_size;
delete[] nodes;
if (num_literals > max_literals_per_metablock ||
num_commands > max_commands_per_metablock) {
break;
}
}
if (last_insert_len > 0) {
Command cmd(last_insert_len);
commands[num_commands++] = cmd;
num_literals += last_insert_len;
}
const bool is_last = (metablock_start + metablock_size == input_size);
uint8_t* storage = NULL;
size_t storage_ix = last_byte_bits;
if (metablock_size == 0) {
// Write the ISLAST and ISEMPTY bits.
storage = new uint8_t[16];
storage[0] = last_byte;
WriteBits(2, 3, &storage_ix, storage);
storage_ix = (storage_ix + 7u) & ~7u;
} else if (!ShouldCompress(input_buffer, mask, metablock_start,
metablock_size, num_literals, num_commands)) {
// Restore the distance cache, as its last update by
// CreateBackwardReferences is now unused.
memcpy(dist_cache, saved_dist_cache, 4 * sizeof(dist_cache[0]));
storage = new uint8_t[metablock_size + 16];
storage[0] = last_byte;
StoreUncompressedMetaBlock(is_last, input_buffer,
metablock_start, mask, metablock_size,
&storage_ix, storage);
} else {
uint32_t num_direct_distance_codes = 0;
uint32_t distance_postfix_bits = 0;
MetaBlockSplit mb;
ContextType literal_context_mode = CONTEXT_UTF8;
if (!IsMostlyUTF8(
input_buffer, metablock_start, mask, metablock_size,
kMinUTF8Ratio)) {
literal_context_mode = CONTEXT_SIGNED;
}
BuildMetaBlock(input_buffer, metablock_start, mask,
prev_byte, prev_byte2,
commands, num_commands,
literal_context_mode,
&mb);
OptimizeHistograms(num_direct_distance_codes,
distance_postfix_bits,
&mb);
const size_t max_out_metablock_size = 2 * metablock_size + 500;
storage = new uint8_t[max_out_metablock_size];
storage[0] = last_byte;
StoreMetaBlock(input_buffer, metablock_start, metablock_size, mask,
prev_byte, prev_byte2,
is_last,
num_direct_distance_codes,
distance_postfix_bits,
literal_context_mode,
commands, num_commands,
mb,
&storage_ix, storage);
if (metablock_size + 4 < (storage_ix >> 3)) {
// Restore the distance cache and last byte.
memcpy(dist_cache, saved_dist_cache, 4 * sizeof(dist_cache[0]));
storage[0] = last_byte;
storage_ix = last_byte_bits;
StoreUncompressedMetaBlock(is_last, input_buffer,
metablock_start, mask,
metablock_size, &storage_ix, storage);
}
}
last_byte = storage[storage_ix >> 3];
last_byte_bits = storage_ix & 7u;
metablock_start += metablock_size;
prev_byte = input_buffer[metablock_start - 1];
prev_byte2 = input_buffer[metablock_start - 2];
// Save the state of the distance cache in case we need to restore it for
// emitting an uncompressed block.
memcpy(saved_dist_cache, dist_cache, 4 * sizeof(dist_cache[0]));
const size_t out_size = storage_ix >> 3;
total_out_size += out_size;
if (total_out_size <= max_out_size) {
memcpy(encoded_buffer, storage, out_size);
encoded_buffer += out_size;
} else {
ok = 0;
}
delete[] storage;
free(commands);
}
*encoded_size = total_out_size;
delete hasher;
return ok;
}
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;
}
if (input_size == 0) {
// Handle the special case of empty input.
*encoded_size = 1;
*encoded_buffer = 6;
return 1;
}
if (params.quality == 10) {
// TODO: Implement this direct path for all quality levels.
const int lgwin = std::min(24, std::max(16, params.lgwin));
return BrotliCompressBufferQuality10(lgwin, input_size, input_buffer,
encoded_size, encoded_buffer);
}
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;
}
static bool BrotliInIsFinished(BrotliIn* r) {
size_t read_bytes;
return r->Read(0, &read_bytes) == NULL;
}
static const uint8_t* BrotliInReadAndCheckEnd(const size_t block_size,
BrotliIn* r,
size_t* bytes_read,
bool* is_last) {
*bytes_read = 0;
const uint8_t* data = reinterpret_cast<const uint8_t*>(
r->Read(block_size, bytes_read));
assert((data == NULL) == (*bytes_read == 0));
*is_last = BrotliInIsFinished(r);
return data;
}
static bool CopyOneBlockToRingBuffer(BrotliIn* r,
BrotliCompressor* compressor,
size_t* bytes_read,
bool* is_last) {
const size_t block_size = compressor->input_block_size();
const uint8_t* data = BrotliInReadAndCheckEnd(block_size, r,
bytes_read, is_last);
if (data == NULL) {
return *is_last;
}
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 = BrotliInReadAndCheckEnd(remaining, r, &more_bytes_read, is_last);
if (data == NULL) {
return *is_last;
}
compressor->CopyInputToRingBuffer(more_bytes_read, data);
*bytes_read += more_bytes_read;
remaining -= more_bytes_read;
}
return true;
}
int BrotliCompress(BrotliParams params, BrotliIn* in, BrotliOut* out) {
return BrotliCompressWithCustomDictionary(0, 0, params, in, out);
}
// Reads the provided input in 'block_size' blocks. Only the last read can be
// smaller than 'block_size'.
class BrotliBlockReader {
public:
explicit BrotliBlockReader(size_t block_size)
: block_size_(block_size), buf_(NULL) {}
~BrotliBlockReader(void) { delete[] buf_; }
const uint8_t* Read(BrotliIn* in, size_t* bytes_read, bool* is_last) {
*bytes_read = 0;
const uint8_t* data = BrotliInReadAndCheckEnd(block_size_, in,
bytes_read, is_last);
if (data == NULL || *bytes_read == block_size_ || *is_last) {
// If we could get the whole block in one read, or it is the last block,
// we just return the pointer to the data without copying.
return data;
}
// If the data comes in smaller chunks, we need to copy it into an internal
// buffer until we get a whole block or reach the last chunk.
if (buf_ == NULL) {
buf_ = new uint8_t[block_size_];
}
memcpy(buf_, data, *bytes_read);
do {
size_t cur_bytes_read = 0;
data = BrotliInReadAndCheckEnd(block_size_ - *bytes_read, in,
&cur_bytes_read, is_last);
if (data == NULL) {
return *is_last ? buf_ : NULL;
}
memcpy(&buf_[*bytes_read], data, cur_bytes_read);
*bytes_read += cur_bytes_read;
} while (*bytes_read < block_size_ && !*is_last);
return buf_;
}
private:
const size_t block_size_;
uint8_t* buf_;
};
int BrotliCompressWithCustomDictionary(size_t dictsize, const uint8_t* dict,
BrotliParams params,
BrotliIn* in, BrotliOut* out) {
if (params.quality <= 1) {
const int quality = std::max(0, params.quality);
const int lgwin = std::min(kMaxWindowBits,
std::max(kMinWindowBits, params.lgwin));
uint8_t* storage = NULL;
int* table = NULL;
uint32_t* command_buf = NULL;
uint8_t* literal_buf = NULL;
uint8_t cmd_depths[128];
uint16_t cmd_bits[128];
uint8_t cmd_code[512];
size_t cmd_code_numbits;
if (quality == 0) {
InitCommandPrefixCodes(cmd_depths, cmd_bits, cmd_code, &cmd_code_numbits);
}
uint8_t last_byte;
uint8_t last_byte_bits;
EncodeWindowBits(lgwin, &last_byte, &last_byte_bits);
BrotliBlockReader r(1u << lgwin);
int ok = 1;
bool is_last = false;
while (ok && !is_last) {
// Read next block of input.
size_t bytes;
const uint8_t* data = r.Read(in, &bytes, &is_last);
if (data == NULL) {
if (!is_last) {
ok = 0;
break;
}
assert(bytes == 0);
}
// Set up output storage.
const size_t max_out_size = 2 * bytes + 500;
if (storage == NULL) {
storage = new uint8_t[max_out_size];
}
storage[0] = last_byte;
size_t storage_ix = last_byte_bits;
// Set up hash table.
size_t htsize = HashTableSize(MaxHashTableSize(quality), bytes);
if (table == NULL) {
table = new int[htsize];
}
memset(table, 0, htsize * sizeof(table[0]));
// Set up command and literal buffers for two pass mode.
if (quality == 1 && command_buf == NULL) {
size_t buf_size = std::min(bytes, kCompressFragmentTwoPassBlockSize);
command_buf = new uint32_t[buf_size];
literal_buf = new uint8_t[buf_size];
}
// Do the actual compression.
if (quality == 0) {
BrotliCompressFragmentFast(data, bytes, is_last, table, htsize,
cmd_depths, cmd_bits,
&cmd_code_numbits, cmd_code,
&storage_ix, storage);
} else {
BrotliCompressFragmentTwoPass(data, bytes, is_last,
command_buf, literal_buf,
table, htsize,
&storage_ix, storage);
}
// Save last bytes to stitch it together with the next output block.
last_byte = storage[storage_ix >> 3];
last_byte_bits = storage_ix & 7u;
// Write output block.
size_t out_bytes = storage_ix >> 3;
if (out_bytes > 0 && !out->Write(storage, out_bytes)) {
ok = 0;
break;
}
}
delete[] storage;
delete[] table;
delete[] command_buf;
delete[] literal_buf;
return ok;
}
size_t in_bytes = 0;
size_t out_bytes = 0;
uint8_t* output = NULL;
bool final_block = false;
BrotliCompressor compressor(params);
if (dictsize != 0) compressor.BrotliSetCustomDictionary(dictsize, dict);
while (!final_block) {
if (!CopyOneBlockToRingBuffer(in, &compressor, &in_bytes, &final_block)) {
return false;
}
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
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