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brotli/enc/brotli_bit_stream.cc
Zoltan Szabadka 534654def1 Add a faster but less dense compression mode. 
The new mode can be used by setting the greedy_block_split
field of BrotliParams to true.

This commit moves all the meta-block processing code
into its own library and moves the meta-block encoding
code to brotli_bit_stream.cc from encode.cc
2015-03-27 14:20:35 +01:00

826 lines
29 KiB
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// Copyright 2014 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.
//
// Brotli bit stream functions to support the low level format. There are no
// compression algorithms here, just the right ordering of bits to match the
// specs.
#include "./brotli_bit_stream.h"
#include <algorithm>
#include <limits>
#include <vector>
#include "./bit_cost.h"
#include "./context.h"
#include "./entropy_encode.h"
#include "./fast_log.h"
#include "./prefix.h"
#include "./write_bits.h"
namespace brotli {
// returns false if fail
// nibblesbits represents the 2 bits to encode MNIBBLES (0-3)
bool EncodeMlen(size_t length, int* bits, int* numbits, int* nibblesbits) {
length--; // MLEN - 1 is encoded
int lg = length == 0 ? 1 : Log2Floor(length) + 1;
if (lg > 28) return false;
int mnibbles = (lg < 16 ? 16 : (lg + 3)) / 4;
*nibblesbits = mnibbles - 4;
*numbits = mnibbles * 4;
*bits = length;
return true;
}
void StoreVarLenUint8(int n, int* storage_ix, uint8_t* storage) {
if (n == 0) {
WriteBits(1, 0, storage_ix, storage);
} else {
WriteBits(1, 1, storage_ix, storage);
int nbits = Log2Floor(n);
WriteBits(3, nbits, storage_ix, storage);
WriteBits(nbits, n - (1 << nbits), storage_ix, storage);
}
}
bool StoreCompressedMetaBlockHeader(bool final_block,
size_t length,
int* storage_ix,
uint8_t* storage) {
// Write ISLAST bit.
WriteBits(1, final_block, storage_ix, storage);
// Write ISEMPTY bit.
if (final_block) {
WriteBits(1, length == 0, storage_ix, storage);
if (length == 0) {
return true;
}
}
if (length == 0) {
// Only the last meta-block can be empty.
return false;
}
int lenbits;
int nlenbits;
int nibblesbits;
if (!EncodeMlen(length, &lenbits, &nlenbits, &nibblesbits)) {
return false;
}
WriteBits(2, nibblesbits, storage_ix, storage);
WriteBits(nlenbits, lenbits, storage_ix, storage);
if (!final_block) {
// Write ISUNCOMPRESSED bit.
WriteBits(1, 0, storage_ix, storage);
}
return true;
}
bool StoreUncompressedMetaBlockHeader(size_t length,
int* storage_ix,
uint8_t* storage) {
// Write ISLAST bit. Uncompressed block cannot be the last one, so set to 0.
WriteBits(1, 0, storage_ix, storage);
int lenbits;
int nlenbits;
int nibblesbits;
if (!EncodeMlen(length, &lenbits, &nlenbits, &nibblesbits)) {
return false;
}
WriteBits(2, nibblesbits, storage_ix, storage);
WriteBits(nlenbits, lenbits, storage_ix, storage);
// Write ISUNCOMPRESSED bit.
WriteBits(1, 1, storage_ix, storage);
return true;
}
void StoreHuffmanTreeOfHuffmanTreeToBitMask(
const int num_codes,
const uint8_t *code_length_bitdepth,
int *storage_ix,
uint8_t *storage) {
static const uint8_t kStorageOrder[kCodeLengthCodes] = {
1, 2, 3, 4, 0, 5, 17, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15
};
// The bit lengths of the Huffman code over the code length alphabet
// are compressed with the following static Huffman code:
// Symbol Code
// ------ ----
// 0 00
// 1 1110
// 2 110
// 3 01
// 4 10
// 5 1111
static const uint8_t kHuffmanBitLengthHuffmanCodeSymbols[6] = {
0, 7, 3, 2, 1, 15
};
static const uint8_t kHuffmanBitLengthHuffmanCodeBitLengths[6] = {
2, 4, 3, 2, 2, 4
};
// Throw away trailing zeros:
int codes_to_store = kCodeLengthCodes;
if (num_codes > 1) {
for (; codes_to_store > 0; --codes_to_store) {
if (code_length_bitdepth[kStorageOrder[codes_to_store - 1]] != 0) {
break;
}
}
}
int skip_some = 0; // skips none.
if (code_length_bitdepth[kStorageOrder[0]] == 0 &&
code_length_bitdepth[kStorageOrder[1]] == 0) {
skip_some = 2; // skips two.
if (code_length_bitdepth[kStorageOrder[2]] == 0) {
skip_some = 3; // skips three.
}
}
WriteBits(2, skip_some, storage_ix, storage);
for (int i = skip_some; i < codes_to_store; ++i) {
uint8_t l = code_length_bitdepth[kStorageOrder[i]];
WriteBits(kHuffmanBitLengthHuffmanCodeBitLengths[l],
kHuffmanBitLengthHuffmanCodeSymbols[l], storage_ix, storage);
}
}
void StoreHuffmanTreeToBitMask(
const std::vector<uint8_t> &huffman_tree,
const std::vector<uint8_t> &huffman_tree_extra_bits,
const uint8_t *code_length_bitdepth,
const std::vector<uint16_t> &code_length_bitdepth_symbols,
int * __restrict storage_ix,
uint8_t * __restrict storage) {
for (int i = 0; i < huffman_tree.size(); ++i) {
int ix = huffman_tree[i];
WriteBits(code_length_bitdepth[ix], code_length_bitdepth_symbols[ix],
storage_ix, storage);
// Extra bits
switch (ix) {
case 16:
WriteBits(2, huffman_tree_extra_bits[i], storage_ix, storage);
break;
case 17:
WriteBits(3, huffman_tree_extra_bits[i], storage_ix, storage);
break;
}
}
}
void StoreSimpleHuffmanTree(const uint8_t* depths,
int symbols[4],
int num_symbols,
int max_bits,
int *storage_ix, uint8_t *storage) {
// value of 1 indicates a simple Huffman code
WriteBits(2, 1, storage_ix, storage);
WriteBits(2, num_symbols - 1, storage_ix, storage); // NSYM - 1
// Sort
for (int i = 0; i < num_symbols; i++) {
for (int j = i + 1; j < num_symbols; j++) {
if (depths[symbols[j]] < depths[symbols[i]]) {
std::swap(symbols[j], symbols[i]);
}
}
}
if (num_symbols == 2) {
WriteBits(max_bits, symbols[0], storage_ix, storage);
WriteBits(max_bits, symbols[1], storage_ix, storage);
} else if (num_symbols == 3) {
WriteBits(max_bits, symbols[0], storage_ix, storage);
WriteBits(max_bits, symbols[1], storage_ix, storage);
WriteBits(max_bits, symbols[2], storage_ix, storage);
} else {
WriteBits(max_bits, symbols[0], storage_ix, storage);
WriteBits(max_bits, symbols[1], storage_ix, storage);
WriteBits(max_bits, symbols[2], storage_ix, storage);
WriteBits(max_bits, symbols[3], storage_ix, storage);
// tree-select
WriteBits(1, depths[symbols[0]] == 1 ? 1 : 0, storage_ix, storage);
}
}
// num = alphabet size
// depths = symbol depths
void StoreHuffmanTree(const uint8_t* depths, size_t num,
int quality,
int *storage_ix, uint8_t *storage) {
// Write the Huffman tree into the brotli-representation.
std::vector<uint8_t> huffman_tree;
std::vector<uint8_t> huffman_tree_extra_bits;
// TODO: Consider allocating these from stack.
huffman_tree.reserve(256);
huffman_tree_extra_bits.reserve(256);
WriteHuffmanTree(depths, num, &huffman_tree, &huffman_tree_extra_bits);
// Calculate the statistics of the Huffman tree in brotli-representation.
int huffman_tree_histogram[kCodeLengthCodes] = { 0 };
for (int i = 0; i < huffman_tree.size(); ++i) {
++huffman_tree_histogram[huffman_tree[i]];
}
int num_codes = 0;
int code = 0;
for (int i = 0; i < kCodeLengthCodes; ++i) {
if (huffman_tree_histogram[i]) {
if (num_codes == 0) {
code = i;
num_codes = 1;
} else if (num_codes == 1) {
num_codes = 2;
break;
}
}
}
// Calculate another Huffman tree to use for compressing both the
// earlier Huffman tree with.
// TODO: Consider allocating these from stack.
uint8_t code_length_bitdepth[kCodeLengthCodes] = { 0 };
std::vector<uint16_t> code_length_bitdepth_symbols(kCodeLengthCodes);
CreateHuffmanTree(&huffman_tree_histogram[0], kCodeLengthCodes,
5, quality, &code_length_bitdepth[0]);
ConvertBitDepthsToSymbols(code_length_bitdepth, kCodeLengthCodes,
code_length_bitdepth_symbols.data());
// Now, we have all the data, let's start storing it
StoreHuffmanTreeOfHuffmanTreeToBitMask(num_codes, code_length_bitdepth,
storage_ix, storage);
if (num_codes == 1) {
code_length_bitdepth[code] = 0;
}
// Store the real huffman tree now.
StoreHuffmanTreeToBitMask(huffman_tree,
huffman_tree_extra_bits,
&code_length_bitdepth[0],
code_length_bitdepth_symbols,
storage_ix, storage);
}
void BuildAndStoreHuffmanTree(const int *histogram,
const int length,
const int quality,
uint8_t* depth,
uint16_t* bits,
int* storage_ix,
uint8_t* storage) {
int count = 0;
int s4[4] = { 0 };
for (size_t i = 0; i < length; i++) {
if (histogram[i]) {
if (count < 4) {
s4[count] = i;
} else if (quality < 3 && count > 4) {
break;
}
count++;
}
}
int max_bits_counter = length - 1;
int max_bits = 0;
while (max_bits_counter) {
max_bits_counter >>= 1;
++max_bits;
}
if (count <= 1) {
WriteBits(4, 1, storage_ix, storage);
WriteBits(max_bits, s4[0], storage_ix, storage);
return;
}
if (length >= 50 && count >= 16 && quality >= 3) {
std::vector<int> counts(length);
memcpy(&counts[0], histogram, sizeof(counts[0]) * length);
OptimizeHuffmanCountsForRle(length, &counts[0]);
CreateHuffmanTree(&counts[0], length, 15, quality, depth);
} else {
CreateHuffmanTree(histogram, length, 15, quality, depth);
}
ConvertBitDepthsToSymbols(depth, length, bits);
if (count <= 4) {
StoreSimpleHuffmanTree(depth, s4, count, max_bits, storage_ix, storage);
} else {
StoreHuffmanTree(depth, length, quality, storage_ix, storage);
}
}
int IndexOf(const std::vector<int>& v, int value) {
for (int i = 0; i < v.size(); ++i) {
if (v[i] == value) return i;
}
return -1;
}
void MoveToFront(std::vector<int>* v, int index) {
int value = (*v)[index];
for (int i = index; i > 0; --i) {
(*v)[i] = (*v)[i - 1];
}
(*v)[0] = value;
}
std::vector<int> MoveToFrontTransform(const std::vector<int>& v) {
if (v.empty()) return v;
std::vector<int> mtf(*std::max_element(v.begin(), v.end()) + 1);
for (int i = 0; i < mtf.size(); ++i) mtf[i] = i;
std::vector<int> result(v.size());
for (int i = 0; i < v.size(); ++i) {
int index = IndexOf(mtf, v[i]);
result[i] = index;
MoveToFront(&mtf, index);
}
return result;
}
// Finds runs of zeros in v_in and replaces them with a prefix code of the run
// length plus extra bits in *v_out and *extra_bits. Non-zero values in v_in are
// shifted by *max_length_prefix. Will not create prefix codes bigger than the
// initial value of *max_run_length_prefix. The prefix code of run length L is
// simply Log2Floor(L) and the number of extra bits is the same as the prefix
// code.
void RunLengthCodeZeros(const std::vector<int>& v_in,
int* max_run_length_prefix,
std::vector<int>* v_out,
std::vector<int>* extra_bits) {
int max_reps = 0;
for (int i = 0; i < v_in.size();) {
for (; i < v_in.size() && v_in[i] != 0; ++i) ;
int reps = 0;
for (; i < v_in.size() && v_in[i] == 0; ++i) {
++reps;
}
max_reps = std::max(reps, max_reps);
}
int max_prefix = max_reps > 0 ? Log2Floor(max_reps) : 0;
*max_run_length_prefix = std::min(max_prefix, *max_run_length_prefix);
for (int i = 0; i < v_in.size();) {
if (v_in[i] != 0) {
v_out->push_back(v_in[i] + *max_run_length_prefix);
extra_bits->push_back(0);
++i;
} else {
int reps = 1;
for (uint32_t k = i + 1; k < v_in.size() && v_in[k] == 0; ++k) {
++reps;
}
i += reps;
while (reps) {
if (reps < (2 << *max_run_length_prefix)) {
int run_length_prefix = Log2Floor(reps);
v_out->push_back(run_length_prefix);
extra_bits->push_back(reps - (1 << run_length_prefix));
break;
} else {
v_out->push_back(*max_run_length_prefix);
extra_bits->push_back((1 << *max_run_length_prefix) - 1);
reps -= (2 << *max_run_length_prefix) - 1;
}
}
}
}
}
// Returns a maximum zero-run-length-prefix value such that run-length coding
// zeros in v with this maximum prefix value and then encoding the resulting
// histogram and entropy-coding v produces the least amount of bits.
int BestMaxZeroRunLengthPrefix(const std::vector<int>& v) {
int min_cost = std::numeric_limits<int>::max();
int best_max_prefix = 0;
for (int max_prefix = 0; max_prefix <= 16; ++max_prefix) {
std::vector<int> rle_symbols;
std::vector<int> extra_bits;
int max_run_length_prefix = max_prefix;
RunLengthCodeZeros(v, &max_run_length_prefix, &rle_symbols, &extra_bits);
if (max_run_length_prefix < max_prefix) break;
HistogramContextMap histogram;
for (int i = 0; i < rle_symbols.size(); ++i) {
histogram.Add(rle_symbols[i]);
}
int bit_cost = PopulationCost(histogram);
if (max_prefix > 0) {
bit_cost += 4;
}
for (int i = 1; i <= max_prefix; ++i) {
bit_cost += histogram.data_[i] * i; // extra bits
}
if (bit_cost < min_cost) {
min_cost = bit_cost;
best_max_prefix = max_prefix;
}
}
return best_max_prefix;
}
void EncodeContextMap(const std::vector<int>& context_map,
int num_clusters,
int* storage_ix, uint8_t* storage) {
StoreVarLenUint8(num_clusters - 1, storage_ix, storage);
if (num_clusters == 1) {
return;
}
std::vector<int> transformed_symbols = MoveToFrontTransform(context_map);
std::vector<int> rle_symbols;
std::vector<int> extra_bits;
int max_run_length_prefix = BestMaxZeroRunLengthPrefix(transformed_symbols);
RunLengthCodeZeros(transformed_symbols, &max_run_length_prefix,
&rle_symbols, &extra_bits);
HistogramContextMap symbol_histogram;
for (int i = 0; i < rle_symbols.size(); ++i) {
symbol_histogram.Add(rle_symbols[i]);
}
bool use_rle = max_run_length_prefix > 0;
WriteBits(1, use_rle, storage_ix, storage);
if (use_rle) {
WriteBits(4, max_run_length_prefix - 1, storage_ix, storage);
}
EntropyCodeContextMap symbol_code;
memset(symbol_code.depth_, 0, sizeof(symbol_code.depth_));
memset(symbol_code.bits_, 0, sizeof(symbol_code.bits_));
BuildAndStoreHuffmanTree(symbol_histogram.data_,
num_clusters + max_run_length_prefix,
9, // quality
symbol_code.depth_, symbol_code.bits_,
storage_ix, storage);
for (int i = 0; i < rle_symbols.size(); ++i) {
WriteBits(symbol_code.depth_[rle_symbols[i]],
symbol_code.bits_[rle_symbols[i]],
storage_ix, storage);
if (rle_symbols[i] > 0 && rle_symbols[i] <= max_run_length_prefix) {
WriteBits(rle_symbols[i], extra_bits[i], storage_ix, storage);
}
}
WriteBits(1, 1, storage_ix, storage); // use move-to-front
}
void StoreBlockSwitch(const BlockSplitCode& code,
const int block_ix,
int* storage_ix,
uint8_t* storage) {
if (block_ix > 0) {
int typecode = code.type_code[block_ix];
WriteBits(code.type_depths[typecode], code.type_bits[typecode],
storage_ix, storage);
}
int lencode = code.length_prefix[block_ix];
WriteBits(code.length_depths[lencode], code.length_bits[lencode],
storage_ix, storage);
WriteBits(code.length_nextra[block_ix], code.length_extra[block_ix],
storage_ix, storage);
}
void BuildAndStoreBlockSplitCode(const std::vector<int>& types,
const std::vector<int>& lengths,
const int num_types,
const int quality,
BlockSplitCode* code,
int* storage_ix,
uint8_t* storage) {
const int num_blocks = types.size();
std::vector<int> type_histo(num_types + 2);
std::vector<int> length_histo(26);
int last_type = 1;
int second_last_type = 0;
code->type_code.resize(num_blocks);
code->length_prefix.resize(num_blocks);
code->length_nextra.resize(num_blocks);
code->length_extra.resize(num_blocks);
code->type_depths.resize(num_types + 2);
code->type_bits.resize(num_types + 2);
code->length_depths.resize(26);
code->length_bits.resize(26);
for (int i = 0; i < num_blocks; ++i) {
int type = types[i];
int type_code = (type == last_type + 1 ? 1 :
type == second_last_type ? 0 :
type + 2);
second_last_type = last_type;
last_type = type;
code->type_code[i] = type_code;
if (i > 0) ++type_histo[type_code];
GetBlockLengthPrefixCode(lengths[i],
&code->length_prefix[i],
&code->length_nextra[i],
&code->length_extra[i]);
++length_histo[code->length_prefix[i]];
}
StoreVarLenUint8(num_types - 1, storage_ix, storage);
if (num_types > 1) {
BuildAndStoreHuffmanTree(&type_histo[0], num_types + 2, quality,
&code->type_depths[0], &code->type_bits[0],
storage_ix, storage);
BuildAndStoreHuffmanTree(&length_histo[0], 26, quality,
&code->length_depths[0], &code->length_bits[0],
storage_ix, storage);
StoreBlockSwitch(*code, 0, storage_ix, storage);
}
}
void StoreTrivialContextMap(int num_types,
int context_bits,
int* storage_ix,
uint8_t* storage) {
StoreVarLenUint8(num_types - 1, storage_ix, storage);
if (num_types > 1) {
int repeat_code = context_bits - 1;
int repeat_bits = (1 << repeat_code) - 1;
int alphabet_size = num_types + repeat_code;
std::vector<int> histogram(alphabet_size);
std::vector<uint8_t> depths(alphabet_size);
std::vector<uint16_t> bits(alphabet_size);
// Write RLEMAX.
WriteBits(1, 1, storage_ix, storage);
WriteBits(4, repeat_code - 1, storage_ix, storage);
histogram[repeat_code] = num_types;
histogram[0] = 1;
for (int i = context_bits; i < alphabet_size; ++i) {
histogram[i] = 1;
}
BuildAndStoreHuffmanTree(&histogram[0], alphabet_size, 1,
&depths[0], &bits[0],
storage_ix, storage);
for (int i = 0; i < num_types; ++i) {
int code = (i == 0 ? 0 : i + context_bits - 1);
WriteBits(depths[code], bits[code], storage_ix, storage);
WriteBits(depths[repeat_code], bits[repeat_code], storage_ix, storage);
WriteBits(repeat_code, repeat_bits, storage_ix, storage);
}
// Write IMTF (inverse-move-to-front) bit.
WriteBits(1, 1, storage_ix, storage);
}
}
// Manages the encoding of one block category (literal, command or distance).
class BlockEncoder {
public:
BlockEncoder(int alphabet_size,
int num_block_types,
const std::vector<int>& block_types,
const std::vector<int>& block_lengths)
: alphabet_size_(alphabet_size),
num_block_types_(num_block_types),
block_types_(block_types),
block_lengths_(block_lengths),
block_ix_(0),
block_len_(block_lengths.empty() ? 0 : block_lengths[0]),
entropy_ix_(0) {}
// Creates entropy codes of block lengths and block types and stores them
// to the bit stream.
void BuildAndStoreBlockSwitchEntropyCodes(int quality,
int* storage_ix, uint8_t* storage) {
BuildAndStoreBlockSplitCode(
block_types_, block_lengths_, num_block_types_,
quality, &block_split_code_, storage_ix, storage);
}
// Creates entropy codes for all block types and stores them to the bit
// stream.
template<int kSize>
void BuildAndStoreEntropyCodes(
const std::vector<Histogram<kSize> >& histograms,
int quality,
int* storage_ix, uint8_t* storage) {
depths_.resize(histograms.size() * alphabet_size_);
bits_.resize(histograms.size() * alphabet_size_);
for (int i = 0; i < histograms.size(); ++i) {
int ix = i * alphabet_size_;
BuildAndStoreHuffmanTree(&histograms[i].data_[0], alphabet_size_,
quality,
&depths_[ix], &bits_[ix],
storage_ix, storage);
}
}
// Stores the next symbol with the entropy code of the current block type.
// Updates the block type and block length at block boundaries.
void StoreSymbol(int symbol, int* storage_ix, uint8_t* storage) {
if (block_len_ == 0) {
++block_ix_;
block_len_ = block_lengths_[block_ix_];
entropy_ix_ = block_types_[block_ix_] * alphabet_size_;
StoreBlockSwitch(block_split_code_, block_ix_, storage_ix, storage);
}
--block_len_;
int ix = entropy_ix_ + symbol;
WriteBits(depths_[ix], bits_[ix], storage_ix, storage);
}
// Stores the next symbol with the entropy code of the current block type and
// context value.
// Updates the block type and block length at block boundaries.
template<int kContextBits>
void StoreSymbolWithContext(int symbol, int context,
const std::vector<int>& context_map,
int* storage_ix, uint8_t* storage) {
if (block_len_ == 0) {
++block_ix_;
block_len_ = block_lengths_[block_ix_];
entropy_ix_ = block_types_[block_ix_] << kContextBits;
StoreBlockSwitch(block_split_code_, block_ix_, storage_ix, storage);
}
--block_len_;
int histo_ix = context_map[entropy_ix_ + context];
int ix = histo_ix * alphabet_size_ + symbol;
WriteBits(depths_[ix], bits_[ix], storage_ix, storage);
}
private:
const int alphabet_size_;
const int num_block_types_;
const std::vector<int>& block_types_;
const std::vector<int>& block_lengths_;
BlockSplitCode block_split_code_;
int block_ix_;
int block_len_;
int entropy_ix_;
std::vector<uint8_t> depths_;
std::vector<uint16_t> bits_;
};
bool StoreMetaBlock(const uint8_t* input,
size_t start_pos,
size_t length,
size_t mask,
bool is_last,
int quality,
int num_direct_distance_codes,
int distance_postfix_bits,
int literal_context_mode,
const brotli::Command *commands,
size_t n_commands,
const MetaBlockSplit& mb,
int *storage_ix,
uint8_t *storage) {
if (!StoreCompressedMetaBlockHeader(is_last, length, storage_ix, storage)) {
return false;
}
if (length == 0) {
return true;
}
int num_distance_codes =
kNumDistanceShortCodes + num_direct_distance_codes +
(48 << distance_postfix_bits);
BlockEncoder literal_enc(256,
mb.literal_split.num_types,
mb.literal_split.types,
mb.literal_split.lengths);
BlockEncoder command_enc(kNumCommandPrefixes,
mb.command_split.num_types,
mb.command_split.types,
mb.command_split.lengths);
BlockEncoder distance_enc(num_distance_codes,
mb.distance_split.num_types,
mb.distance_split.types,
mb.distance_split.lengths);
literal_enc.BuildAndStoreBlockSwitchEntropyCodes(
quality, storage_ix, storage);
command_enc.BuildAndStoreBlockSwitchEntropyCodes(
quality, storage_ix, storage);
distance_enc.BuildAndStoreBlockSwitchEntropyCodes(
quality, storage_ix, storage);
WriteBits(2, distance_postfix_bits, storage_ix, storage);
WriteBits(4, num_direct_distance_codes >> distance_postfix_bits,
storage_ix, storage);
for (int i = 0; i < mb.literal_split.num_types; ++i) {
WriteBits(2, literal_context_mode, storage_ix, storage);
}
if (mb.literal_context_map.empty()) {
StoreTrivialContextMap(mb.literal_histograms.size(), kLiteralContextBits,
storage_ix, storage);
} else {
EncodeContextMap(mb.literal_context_map, mb.literal_histograms.size(),
storage_ix, storage);
}
if (mb.distance_context_map.empty()) {
StoreTrivialContextMap(mb.distance_histograms.size(), kDistanceContextBits,
storage_ix, storage);
} else {
EncodeContextMap(mb.distance_context_map, mb.distance_histograms.size(),
storage_ix, storage);
}
literal_enc.BuildAndStoreEntropyCodes(mb.literal_histograms, quality,
storage_ix, storage);
command_enc.BuildAndStoreEntropyCodes(mb.command_histograms, quality,
storage_ix, storage);
distance_enc.BuildAndStoreEntropyCodes(mb.distance_histograms, quality,
storage_ix, storage);
size_t pos = start_pos;
for (int i = 0; i < n_commands; ++i) {
const Command cmd = commands[i];
int cmd_code = cmd.cmd_prefix_;
int lennumextra = cmd.cmd_extra_ >> 48;
uint64_t lenextra = cmd.cmd_extra_ & 0xffffffffffffULL;
command_enc.StoreSymbol(cmd_code, storage_ix, storage);
WriteBits(lennumextra, lenextra, storage_ix, storage);
if (mb.literal_context_map.empty()) {
for (int j = 0; j < cmd.insert_len_; j++) {
literal_enc.StoreSymbol(input[pos & mask], storage_ix, storage);
++pos;
}
} else {
for (int j = 0; j < cmd.insert_len_; ++j) {
uint8_t prev_byte = pos > 0 ? input[(pos - 1) & mask] : 0;
uint8_t prev_byte2 = pos > 1 ? input[(pos - 2) & mask] : 0;
int context = Context(prev_byte, prev_byte2,
literal_context_mode);
int literal = input[pos & mask];
literal_enc.StoreSymbolWithContext<kLiteralContextBits>(
literal, context, mb.literal_context_map, storage_ix, storage);
++pos;
}
}
if (cmd.copy_len_ > 0 && cmd.cmd_prefix_ >= 128) {
int dist_code = cmd.dist_prefix_;
int distnumextra = cmd.dist_extra_ >> 24;
int distextra = cmd.dist_extra_ & 0xffffff;
if (mb.distance_context_map.empty()) {
distance_enc.StoreSymbol(dist_code, storage_ix, storage);
} else {
int context = cmd.DistanceContext();
distance_enc.StoreSymbolWithContext<kDistanceContextBits>(
dist_code, context, mb.distance_context_map, storage_ix, storage);
}
brotli::WriteBits(distnumextra, distextra, storage_ix, storage);
}
pos += cmd.copy_len_;
}
return true;
}
// This is for storing uncompressed blocks (simple raw storage of
// bytes-as-bytes).
bool StoreUncompressedMetaBlock(bool final_block,
const uint8_t * __restrict input,
size_t position, size_t mask,
size_t len,
int * __restrict storage_ix,
uint8_t * __restrict storage) {
if (!brotli::StoreUncompressedMetaBlockHeader(len, storage_ix, storage)) {
return false;
}
*storage_ix = ((*storage_ix + 7) / 8) * 8; // Go to next byte
size_t masked_pos = position & mask;
if (masked_pos + len > mask + 1) {
size_t len1 = mask + 1 - masked_pos;
memcpy(&storage[*storage_ix >> 3], &input[masked_pos], len1);
*storage_ix += len1 << 3;
len -= len1;
masked_pos = 0;
}
memcpy(&storage[*storage_ix >> 3], &input[masked_pos], len);
*storage_ix += len << 3;
// We need to clear the next 4 bytes to continue to be
// compatible with WriteBits.
brotli::WriteBitsPrepareStorage(*storage_ix, storage);
// Since the uncomressed block itself may not be the final block, add an empty
// one after this.
if (final_block) {
brotli::WriteBits(1, 1, storage_ix, storage); // islast
brotli::WriteBits(1, 1, storage_ix, storage); // isempty
*storage_ix = ((*storage_ix + 7) / 8) * 8; // Go to next byte
// We need to clear the next 4 bytes to continue to be
// compatible with WriteBits.
brotli::WriteBitsPrepareStorage(*storage_ix, storage);
}
return true;
}
} // namespace brotli
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