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brotli/enc/brotli_bit_stream.cc
Eugene Kliuchnikov 352b0b2836 Transform most of C++ comments to C-style.
2016-06-03 11:19:23 +02:00

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/* Copyright 2014 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
/* 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 <cstdlib> /* free, malloc */
#include <cstring>
#include <limits>
#include <vector>
#include "../common/types.h"
#include "./bit_cost.h"
#include "./context.h"
#include "./entropy_encode.h"
#include "./entropy_encode_static.h"
#include "./fast_log.h"
#include "./prefix.h"
#include "./write_bits.h"
namespace brotli {
namespace {
static const size_t kMaxHuffmanTreeSize = 2 * kNumCommandPrefixes + 1;
// Context map alphabet has 256 context id symbols plus max 16 rle symbols.
static const size_t kContextMapAlphabetSize = 256 + 16;
// Block type alphabet has 256 block id symbols plus 2 special symbols.
static const size_t kBlockTypeAlphabetSize = 256 + 2;
/* nibblesbits represents the 2 bits to encode MNIBBLES (0-3)
REQUIRES: length > 0
REQUIRES: length <= (1 << 24) */
void EncodeMlen(size_t length, uint64_t* bits,
size_t* numbits, uint64_t* nibblesbits) {
assert(length > 0);
assert(length <= (1 << 24));
length--; // MLEN - 1 is encoded
size_t lg = length == 0 ? 1 : Log2FloorNonZero(
static_cast<uint32_t>(length)) + 1;
assert(lg <= 24);
size_t mnibbles = (lg < 16 ? 16 : (lg + 3)) / 4;
*nibblesbits = mnibbles - 4;
*numbits = mnibbles * 4;
*bits = length;
}
static inline void StoreCommandExtra(
const Command& cmd, size_t* storage_ix, uint8_t* storage) {
uint32_t copylen_code = cmd.copy_len_code();
uint16_t inscode = GetInsertLengthCode(cmd.insert_len_);
uint16_t copycode = GetCopyLengthCode(copylen_code);
uint32_t insnumextra = GetInsertExtra(inscode);
uint64_t insextraval = cmd.insert_len_ - GetInsertBase(inscode);
uint64_t copyextraval = copylen_code - GetCopyBase(copycode);
uint64_t bits = (copyextraval << insnumextra) | insextraval;
WriteBits(insnumextra + GetCopyExtra(copycode), bits, storage_ix, storage);
}
} // namespace
void StoreVarLenUint8(size_t n, size_t* storage_ix, uint8_t* storage) {
if (n == 0) {
WriteBits(1, 0, storage_ix, storage);
} else {
WriteBits(1, 1, storage_ix, storage);
size_t nbits = Log2FloorNonZero(n);
WriteBits(3, nbits, storage_ix, storage);
WriteBits(nbits, n - (1 << nbits), storage_ix, storage);
}
}
/* Stores the compressed meta-block header.
REQUIRES: length > 0
REQUIRES: length <= (1 << 24) */
void StoreCompressedMetaBlockHeader(bool final_block,
size_t length,
size_t* storage_ix,
uint8_t* storage) {
/* Write ISLAST bit. */
WriteBits(1, final_block, storage_ix, storage);
/* Write ISEMPTY bit. */
if (final_block) {
WriteBits(1, 0, storage_ix, storage);
}
uint64_t lenbits;
size_t nlenbits;
uint64_t nibblesbits;
EncodeMlen(length, &lenbits, &nlenbits, &nibblesbits);
WriteBits(2, nibblesbits, storage_ix, storage);
WriteBits(nlenbits, lenbits, storage_ix, storage);
if (!final_block) {
/* Write ISUNCOMPRESSED bit. */
WriteBits(1, 0, storage_ix, storage);
}
}
/* Stores the uncompressed meta-block header.
REQUIRES: length > 0
REQUIRES: length <= (1 << 24) */
void StoreUncompressedMetaBlockHeader(size_t length,
size_t* 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);
uint64_t lenbits;
size_t nlenbits;
uint64_t nibblesbits;
EncodeMlen(length, &lenbits, &nlenbits, &nibblesbits);
WriteBits(2, nibblesbits, storage_ix, storage);
WriteBits(nlenbits, lenbits, storage_ix, storage);
/* Write ISUNCOMPRESSED bit. */
WriteBits(1, 1, storage_ix, storage);
}
void StoreHuffmanTreeOfHuffmanTreeToBitMask(
const int num_codes,
const uint8_t *code_length_bitdepth,
size_t *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: */
size_t 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;
}
}
}
size_t 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 (size_t i = skip_some; i < codes_to_store; ++i) {
size_t l = code_length_bitdepth[kStorageOrder[i]];
WriteBits(kHuffmanBitLengthHuffmanCodeBitLengths[l],
kHuffmanBitLengthHuffmanCodeSymbols[l], storage_ix, storage);
}
}
static void StoreHuffmanTreeToBitMask(
const size_t huffman_tree_size,
const uint8_t* huffman_tree,
const uint8_t* huffman_tree_extra_bits,
const uint8_t* code_length_bitdepth,
const uint16_t* code_length_bitdepth_symbols,
size_t * __restrict storage_ix,
uint8_t * __restrict storage) {
for (size_t i = 0; i < huffman_tree_size; ++i) {
size_t 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;
}
}
}
static void StoreSimpleHuffmanTree(const uint8_t* depths,
size_t symbols[4],
size_t num_symbols,
size_t max_bits,
size_t *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 (size_t i = 0; i < num_symbols; i++) {
for (size_t 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,
HuffmanTree* tree,
size_t *storage_ix, uint8_t *storage) {
/* Write the Huffman tree into the brotli-representation.
The command alphabet is the largest, so this allocation will fit all
alphabets. */
assert(num <= kNumCommandPrefixes);
uint8_t huffman_tree[kNumCommandPrefixes];
uint8_t huffman_tree_extra_bits[kNumCommandPrefixes];
size_t huffman_tree_size = 0;
WriteHuffmanTree(depths, num, &huffman_tree_size, huffman_tree,
huffman_tree_extra_bits);
/* Calculate the statistics of the Huffman tree in brotli-representation. */
uint32_t huffman_tree_histogram[kCodeLengthCodes] = { 0 };
for (size_t 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. */
uint8_t code_length_bitdepth[kCodeLengthCodes] = { 0 };
uint16_t code_length_bitdepth_symbols[kCodeLengthCodes] = { 0 };
CreateHuffmanTree(&huffman_tree_histogram[0], kCodeLengthCodes,
5, tree, &code_length_bitdepth[0]);
ConvertBitDepthsToSymbols(code_length_bitdepth, kCodeLengthCodes,
&code_length_bitdepth_symbols[0]);
/* 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_size,
huffman_tree,
huffman_tree_extra_bits,
&code_length_bitdepth[0],
code_length_bitdepth_symbols,
storage_ix, storage);
}
/* Builds a Huffman tree from histogram[0:length] into depth[0:length] and
bits[0:length] and stores the encoded tree to the bit stream. */
void BuildAndStoreHuffmanTree(const uint32_t *histogram,
const size_t length,
HuffmanTree* tree,
uint8_t* depth,
uint16_t* bits,
size_t* storage_ix,
uint8_t* storage) {
size_t count = 0;
size_t s4[4] = { 0 };
for (size_t i = 0; i < length; i++) {
if (histogram[i]) {
if (count < 4) {
s4[count] = i;
} else if (count > 4) {
break;
}
count++;
}
}
size_t max_bits_counter = length - 1;
size_t 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;
}
CreateHuffmanTree(histogram, length, 15, tree, depth);
ConvertBitDepthsToSymbols(depth, length, bits);
if (count <= 4) {
StoreSimpleHuffmanTree(depth, s4, count, max_bits, storage_ix, storage);
} else {
StoreHuffmanTree(depth, length, tree, storage_ix, storage);
}
}
static inline bool SortHuffmanTree(const HuffmanTree& v0,
const HuffmanTree& v1) {
return v0.total_count_ < v1.total_count_;
}
void BuildAndStoreHuffmanTreeFast(const uint32_t *histogram,
const size_t histogram_total,
const size_t max_bits,
uint8_t* depth,
uint16_t* bits,
size_t* storage_ix,
uint8_t* storage) {
size_t count = 0;
size_t symbols[4] = { 0 };
size_t length = 0;
size_t total = histogram_total;
while (total != 0) {
if (histogram[length]) {
if (count < 4) {
symbols[count] = length;
}
++count;
total -= histogram[length];
}
++length;
}
if (count <= 1) {
WriteBits(4, 1, storage_ix, storage);
WriteBits(max_bits, symbols[0], storage_ix, storage);
return;
}
const size_t max_tree_size = 2 * length + 1;
HuffmanTree* const tree =
static_cast<HuffmanTree*>(malloc(max_tree_size * sizeof(HuffmanTree)));
for (uint32_t count_limit = 1; ; count_limit *= 2) {
HuffmanTree* node = tree;
for (size_t i = length; i != 0;) {
--i;
if (histogram[i]) {
if (PREDICT_TRUE(histogram[i] >= count_limit)) {
*node = HuffmanTree(histogram[i], -1, static_cast<int16_t>(i));
} else {
*node = HuffmanTree(count_limit, -1, static_cast<int16_t>(i));
}
++node;
}
}
const int n = static_cast<int>(node - tree);
std::sort(tree, node, SortHuffmanTree);
/* The nodes are:
[0, n): the sorted leaf nodes that we start with.
[n]: we add a sentinel here.
[n + 1, 2n): new parent nodes are added here, starting from
(n+1). These are naturally in ascending order.
[2n]: we add a sentinel at the end as well.
There will be (2n+1) elements at the end. */
const HuffmanTree sentinel(std::numeric_limits<int>::max(), -1, -1);
*node++ = sentinel;
*node++ = sentinel;
int i = 0; // Points to the next leaf node.
int j = n + 1; // Points to the next non-leaf node.
for (int k = n - 1; k > 0; --k) {
int left, right;
if (tree[i].total_count_ <= tree[j].total_count_) {
left = i;
++i;
} else {
left = j;
++j;
}
if (tree[i].total_count_ <= tree[j].total_count_) {
right = i;
++i;
} else {
right = j;
++j;
}
/* The sentinel node becomes the parent node. */
node[-1].total_count_ =
tree[left].total_count_ + tree[right].total_count_;
node[-1].index_left_ = static_cast<int16_t>(left);
node[-1].index_right_or_value_ = static_cast<int16_t>(right);
/* Add back the last sentinel node. */
*node++ = sentinel;
}
SetDepth(tree[2 * n - 1], &tree[0], depth, 0);
/* We need to pack the Huffman tree in 14 bits. If this was not
successful, add fake entities to the lowest values and retry. */
if (PREDICT_TRUE(*std::max_element(&depth[0], &depth[length]) <= 14)) {
break;
}
}
free(tree);
ConvertBitDepthsToSymbols(depth, length, bits);
if (count <= 4) {
/* value of 1 indicates a simple Huffman code */
WriteBits(2, 1, storage_ix, storage);
WriteBits(2, count - 1, storage_ix, storage); /* NSYM - 1 */
/* Sort */
for (size_t i = 0; i < count; i++) {
for (size_t j = i + 1; j < count; j++) {
if (depth[symbols[j]] < depth[symbols[i]]) {
std::swap(symbols[j], symbols[i]);
}
}
}
if (count == 2) {
WriteBits(max_bits, symbols[0], storage_ix, storage);
WriteBits(max_bits, symbols[1], storage_ix, storage);
} else if (count == 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, depth[symbols[0]] == 1 ? 1 : 0, storage_ix, storage);
}
} else {
/* Complex Huffman Tree */
StoreStaticCodeLengthCode(storage_ix, storage);
/* Actual rle coding. */
uint8_t previous_value = 8;
for (size_t i = 0; i < length;) {
const uint8_t value = depth[i];
size_t reps = 1;
for (size_t k = i + 1; k < length && depth[k] == value; ++k) {
++reps;
}
i += reps;
if (value == 0) {
WriteBits(kZeroRepsDepth[reps], kZeroRepsBits[reps],
storage_ix, storage);
} else {
if (previous_value != value) {
WriteBits(kCodeLengthDepth[value], kCodeLengthBits[value],
storage_ix, storage);
--reps;
}
if (reps < 3) {
while (reps != 0) {
reps--;
WriteBits(kCodeLengthDepth[value], kCodeLengthBits[value],
storage_ix, storage);
}
} else {
reps -= 3;
WriteBits(kNonZeroRepsDepth[reps], kNonZeroRepsBits[reps],
storage_ix, storage);
}
previous_value = value;
}
}
}
}
static size_t IndexOf(const uint8_t* v, size_t v_size, uint8_t value) {
size_t i = 0;
for (; i < v_size; ++i) {
if (v[i] == value) return i;
}
return i;
}
static void MoveToFront(uint8_t* v, size_t index) {
uint8_t value = v[index];
for (size_t i = index; i != 0; --i) {
v[i] = v[i - 1];
}
v[0] = value;
}
static void MoveToFrontTransform(const uint32_t* __restrict v_in,
const size_t v_size,
uint32_t* v_out) {
if (v_size == 0) {
return;
}
uint32_t max_value = *std::max_element(v_in, v_in + v_size);
assert(max_value < 256u);
uint8_t mtf[256];
size_t mtf_size = max_value + 1;
for (uint32_t i = 0; i <= max_value; ++i) {
mtf[i] = static_cast<uint8_t>(i);
}
for (size_t i = 0; i < v_size; ++i) {
size_t index = IndexOf(mtf, mtf_size, static_cast<uint8_t>(v_in[i]));
assert(index < mtf_size);
v_out[i] = static_cast<uint32_t>(index);
MoveToFront(mtf, index);
}
}
/* Finds runs of zeros in v[0..in_size) and replaces them with a prefix code of
the run length plus extra bits (lower 9 bits is the prefix code and the rest
are the extra bits). Non-zero values in v[] 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. */
static void RunLengthCodeZeros(const size_t in_size,
uint32_t* __restrict v,
size_t* __restrict out_size,
uint32_t* __restrict max_run_length_prefix) {
uint32_t max_reps = 0;
for (size_t i = 0; i < in_size;) {
for (; i < in_size && v[i] != 0; ++i) ;
uint32_t reps = 0;
for (; i < in_size && v[i] == 0; ++i) {
++reps;
}
max_reps = std::max(reps, max_reps);
}
uint32_t max_prefix = max_reps > 0 ? Log2FloorNonZero(max_reps) : 0;
max_prefix = std::min(max_prefix, *max_run_length_prefix);
*max_run_length_prefix = max_prefix;
*out_size = 0;
for (size_t i = 0; i < in_size;) {
assert(*out_size <= i);
if (v[i] != 0) {
v[*out_size] = v[i] + *max_run_length_prefix;
++i;
++(*out_size);
} else {
uint32_t reps = 1;
for (size_t k = i + 1; k < in_size && v[k] == 0; ++k) {
++reps;
}
i += reps;
while (reps != 0) {
if (reps < (2u << max_prefix)) {
uint32_t run_length_prefix = Log2FloorNonZero(reps);
const uint32_t extra_bits = reps - (1u << run_length_prefix);
v[*out_size] = run_length_prefix + (extra_bits << 9);
++(*out_size);
break;
} else {
const uint32_t extra_bits = (1u << max_prefix) - 1u;
v[*out_size] = max_prefix + (extra_bits << 9);
reps -= (2u << max_prefix) - 1u;
++(*out_size);
}
}
}
}
}
void EncodeContextMap(const std::vector<uint32_t>& context_map,
size_t num_clusters,
HuffmanTree* tree,
size_t* storage_ix, uint8_t* storage) {
StoreVarLenUint8(num_clusters - 1, storage_ix, storage);
if (num_clusters == 1) {
return;
}
uint32_t* rle_symbols = new uint32_t[context_map.size()];
MoveToFrontTransform(&context_map[0], context_map.size(), rle_symbols);
uint32_t max_run_length_prefix = 6;
size_t num_rle_symbols = 0;
RunLengthCodeZeros(context_map.size(), rle_symbols,
&num_rle_symbols, &max_run_length_prefix);
uint32_t histogram[kContextMapAlphabetSize];
memset(histogram, 0, sizeof(histogram));
static const int kSymbolBits = 9;
static const uint32_t kSymbolMask = (1u << kSymbolBits) - 1u;
for (size_t i = 0; i < num_rle_symbols; ++i) {
++histogram[rle_symbols[i] & kSymbolMask];
}
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);
}
uint8_t depths[kContextMapAlphabetSize];
uint16_t bits[kContextMapAlphabetSize];
memset(depths, 0, sizeof(depths));
memset(bits, 0, sizeof(bits));
BuildAndStoreHuffmanTree(histogram, num_clusters + max_run_length_prefix,
tree, depths, bits, storage_ix, storage);
for (size_t i = 0; i < num_rle_symbols; ++i) {
const uint32_t rle_symbol = rle_symbols[i] & kSymbolMask;
const uint32_t extra_bits_val = rle_symbols[i] >> kSymbolBits;
WriteBits(depths[rle_symbol], bits[rle_symbol], storage_ix, storage);
if (rle_symbol > 0 && rle_symbol <= max_run_length_prefix) {
WriteBits(rle_symbol, extra_bits_val, storage_ix, storage);
}
}
WriteBits(1, 1, storage_ix, storage); // use move-to-front
delete[] rle_symbols;
}
/* Stores the block switch command with index block_ix to the bit stream. */
void StoreBlockSwitch(const BlockSplitCode& code,
const size_t block_ix,
size_t* storage_ix,
uint8_t* storage) {
if (block_ix > 0) {
size_t typecode = code.type_code[block_ix];
WriteBits(code.type_depths[typecode], code.type_bits[typecode],
storage_ix, storage);
}
size_t 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);
}
/* Builds a BlockSplitCode data structure from the block split given by the
vector of block types and block lengths and stores it to the bit stream. */
static void BuildAndStoreBlockSplitCode(const std::vector<uint8_t>& types,
const std::vector<uint32_t>& lengths,
const size_t num_types,
HuffmanTree* tree,
BlockSplitCode* code,
size_t* storage_ix,
uint8_t* storage) {
const size_t num_blocks = types.size();
uint32_t type_histo[kBlockTypeAlphabetSize];
uint32_t length_histo[kNumBlockLenPrefixes];
memset(type_histo, 0, (num_types + 2) * sizeof(type_histo[0]));
memset(length_histo, 0, sizeof(length_histo));
size_t last_type = 1;
size_t 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);
memset(code->length_depths, 0, sizeof(code->length_depths));
memset(code->length_bits, 0, sizeof(code->length_bits));
for (size_t i = 0; i < num_blocks; ++i) {
size_t type = types[i];
size_t 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] = static_cast<uint32_t>(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, tree,
&code->type_depths[0], &code->type_bits[0],
storage_ix, storage);
BuildAndStoreHuffmanTree(&length_histo[0], kNumBlockLenPrefixes, tree,
&code->length_depths[0], &code->length_bits[0],
storage_ix, storage);
StoreBlockSwitch(*code, 0, storage_ix, storage);
}
}
/* Stores a context map where the histogram type is always the block type. */
void StoreTrivialContextMap(size_t num_types,
size_t context_bits,
HuffmanTree* tree,
size_t* storage_ix,
uint8_t* storage) {
StoreVarLenUint8(num_types - 1, storage_ix, storage);
if (num_types > 1) {
size_t repeat_code = context_bits - 1u;
size_t repeat_bits = (1u << repeat_code) - 1u;
size_t alphabet_size = num_types + repeat_code;
uint32_t histogram[kContextMapAlphabetSize];
uint8_t depths[kContextMapAlphabetSize];
uint16_t bits[kContextMapAlphabetSize];
memset(histogram, 0, alphabet_size * sizeof(histogram[0]));
memset(depths, 0, alphabet_size * sizeof(depths[0]));
memset(bits, 0, alphabet_size * sizeof(bits[0]));
/* Write RLEMAX. */
WriteBits(1, 1, storage_ix, storage);
WriteBits(4, repeat_code - 1, storage_ix, storage);
histogram[repeat_code] = static_cast<uint32_t>(num_types);
histogram[0] = 1;
for (size_t i = context_bits; i < alphabet_size; ++i) {
histogram[i] = 1;
}
BuildAndStoreHuffmanTree(&histogram[0], alphabet_size, tree,
&depths[0], &bits[0],
storage_ix, storage);
for (size_t i = 0; i < num_types; ++i) {
size_t 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(size_t alphabet_size,
size_t num_block_types,
const std::vector<uint8_t>& block_types,
const std::vector<uint32_t>& 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(HuffmanTree* tree,
size_t* storage_ix,
uint8_t* storage) {
BuildAndStoreBlockSplitCode(
block_types_, block_lengths_, num_block_types_,
tree, &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,
HuffmanTree* tree,
size_t* storage_ix, uint8_t* storage) {
depths_.resize(histograms.size() * alphabet_size_);
bits_.resize(histograms.size() * alphabet_size_);
for (size_t i = 0; i < histograms.size(); ++i) {
size_t ix = i * alphabet_size_;
BuildAndStoreHuffmanTree(&histograms[i].data_[0], alphabet_size_,
tree,
&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(size_t symbol, size_t* 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_;
size_t 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(size_t symbol, size_t context,
const std::vector<uint32_t>& context_map,
size_t* storage_ix, uint8_t* storage) {
if (block_len_ == 0) {
++block_ix_;
block_len_ = block_lengths_[block_ix_];
size_t block_type = block_types_[block_ix_];
entropy_ix_ = block_type << kContextBits;
StoreBlockSwitch(block_split_code_, block_ix_, storage_ix, storage);
}
--block_len_;
size_t histo_ix = context_map[entropy_ix_ + context];
size_t ix = histo_ix * alphabet_size_ + symbol;
WriteBits(depths_[ix], bits_[ix], storage_ix, storage);
}
private:
const size_t alphabet_size_;
const size_t num_block_types_;
const std::vector<uint8_t>& block_types_;
const std::vector<uint32_t>& block_lengths_;
BlockSplitCode block_split_code_;
size_t block_ix_;
size_t block_len_;
size_t entropy_ix_;
std::vector<uint8_t> depths_;
std::vector<uint16_t> bits_;
};
static void JumpToByteBoundary(size_t* storage_ix, uint8_t* storage) {
*storage_ix = (*storage_ix + 7u) & ~7u;
storage[*storage_ix >> 3] = 0;
}
void StoreMetaBlock(const uint8_t* input,
size_t start_pos,
size_t length,
size_t mask,
uint8_t prev_byte,
uint8_t prev_byte2,
bool is_last,
uint32_t num_direct_distance_codes,
uint32_t distance_postfix_bits,
ContextType literal_context_mode,
const brotli::Command *commands,
size_t n_commands,
const MetaBlockSplit& mb,
size_t *storage_ix,
uint8_t *storage) {
StoreCompressedMetaBlockHeader(is_last, length, storage_ix, storage);
size_t num_distance_codes =
kNumDistanceShortCodes + num_direct_distance_codes +
(48u << distance_postfix_bits);
HuffmanTree* tree = static_cast<HuffmanTree*>(
malloc(kMaxHuffmanTreeSize * sizeof(HuffmanTree)));
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(tree, storage_ix, storage);
command_enc.BuildAndStoreBlockSwitchEntropyCodes(tree, storage_ix, storage);
distance_enc.BuildAndStoreBlockSwitchEntropyCodes(tree, storage_ix, storage);
WriteBits(2, distance_postfix_bits, storage_ix, storage);
WriteBits(4, num_direct_distance_codes >> distance_postfix_bits,
storage_ix, storage);
for (size_t i = 0; i < mb.literal_split.num_types; ++i) {
WriteBits(2, literal_context_mode, storage_ix, storage);
}
size_t num_literal_histograms = mb.literal_histograms.size();
if (mb.literal_context_map.empty()) {
StoreTrivialContextMap(num_literal_histograms, kLiteralContextBits, tree,
storage_ix, storage);
} else {
EncodeContextMap(mb.literal_context_map, num_literal_histograms, tree,
storage_ix, storage);
}
size_t num_dist_histograms = mb.distance_histograms.size();
if (mb.distance_context_map.empty()) {
StoreTrivialContextMap(num_dist_histograms, kDistanceContextBits, tree,
storage_ix, storage);
} else {
EncodeContextMap(mb.distance_context_map, num_dist_histograms, tree,
storage_ix, storage);
}
literal_enc.BuildAndStoreEntropyCodes(mb.literal_histograms, tree,
storage_ix, storage);
command_enc.BuildAndStoreEntropyCodes(mb.command_histograms, tree,
storage_ix, storage);
distance_enc.BuildAndStoreEntropyCodes(mb.distance_histograms, tree,
storage_ix, storage);
free(tree);
size_t pos = start_pos;
for (size_t i = 0; i < n_commands; ++i) {
const Command cmd = commands[i];
size_t cmd_code = cmd.cmd_prefix_;
command_enc.StoreSymbol(cmd_code, storage_ix, storage);
StoreCommandExtra(cmd, storage_ix, storage);
if (mb.literal_context_map.empty()) {
for (size_t j = cmd.insert_len_; j != 0; --j) {
literal_enc.StoreSymbol(input[pos & mask], storage_ix, storage);
++pos;
}
} else {
for (size_t j = cmd.insert_len_; j != 0; --j) {
size_t context = Context(prev_byte, prev_byte2, literal_context_mode);
uint8_t literal = input[pos & mask];
literal_enc.StoreSymbolWithContext<kLiteralContextBits>(
literal, context, mb.literal_context_map, storage_ix, storage);
prev_byte2 = prev_byte;
prev_byte = literal;
++pos;
}
}
pos += cmd.copy_len();
if (cmd.copy_len()) {
prev_byte2 = input[(pos - 2) & mask];
prev_byte = input[(pos - 1) & mask];
if (cmd.cmd_prefix_ >= 128) {
size_t dist_code = cmd.dist_prefix_;
uint32_t distnumextra = cmd.dist_extra_ >> 24;
uint64_t distextra = cmd.dist_extra_ & 0xffffff;
if (mb.distance_context_map.empty()) {
distance_enc.StoreSymbol(dist_code, storage_ix, storage);
} else {
size_t context = cmd.DistanceContext();
distance_enc.StoreSymbolWithContext<kDistanceContextBits>(
dist_code, context, mb.distance_context_map, storage_ix, storage);
}
brotli::WriteBits(distnumextra, distextra, storage_ix, storage);
}
}
}
if (is_last) {
JumpToByteBoundary(storage_ix, storage);
}
}
static void BuildHistograms(const uint8_t* input,
size_t start_pos,
size_t mask,
const brotli::Command *commands,
size_t n_commands,
HistogramLiteral* lit_histo,
HistogramCommand* cmd_histo,
HistogramDistance* dist_histo) {
size_t pos = start_pos;
for (size_t i = 0; i < n_commands; ++i) {
const Command cmd = commands[i];
cmd_histo->Add(cmd.cmd_prefix_);
for (size_t j = cmd.insert_len_; j != 0; --j) {
lit_histo->Add(input[pos & mask]);
++pos;
}
pos += cmd.copy_len();
if (cmd.copy_len() && cmd.cmd_prefix_ >= 128) {
dist_histo->Add(cmd.dist_prefix_);
}
}
}
static void StoreDataWithHuffmanCodes(const uint8_t* input,
size_t start_pos,
size_t mask,
const brotli::Command *commands,
size_t n_commands,
const uint8_t* lit_depth,
const uint16_t* lit_bits,
const uint8_t* cmd_depth,
const uint16_t* cmd_bits,
const uint8_t* dist_depth,
const uint16_t* dist_bits,
size_t* storage_ix,
uint8_t* storage) {
size_t pos = start_pos;
for (size_t i = 0; i < n_commands; ++i) {
const Command cmd = commands[i];
const size_t cmd_code = cmd.cmd_prefix_;
WriteBits(cmd_depth[cmd_code], cmd_bits[cmd_code], storage_ix, storage);
StoreCommandExtra(cmd, storage_ix, storage);
for (size_t j = cmd.insert_len_; j != 0; --j) {
const uint8_t literal = input[pos & mask];
WriteBits(lit_depth[literal], lit_bits[literal], storage_ix, storage);
++pos;
}
pos += cmd.copy_len();
if (cmd.copy_len() && cmd.cmd_prefix_ >= 128) {
const size_t dist_code = cmd.dist_prefix_;
const uint32_t distnumextra = cmd.dist_extra_ >> 24;
const uint32_t distextra = cmd.dist_extra_ & 0xffffff;
WriteBits(dist_depth[dist_code], dist_bits[dist_code],
storage_ix, storage);
WriteBits(distnumextra, distextra, storage_ix, storage);
}
}
}
void StoreMetaBlockTrivial(const uint8_t* input,
size_t start_pos,
size_t length,
size_t mask,
bool is_last,
const brotli::Command *commands,
size_t n_commands,
size_t *storage_ix,
uint8_t *storage) {
StoreCompressedMetaBlockHeader(is_last, length, storage_ix, storage);
HistogramLiteral lit_histo;
HistogramCommand cmd_histo;
HistogramDistance dist_histo;
BuildHistograms(input, start_pos, mask, commands, n_commands,
&lit_histo, &cmd_histo, &dist_histo);
WriteBits(13, 0, storage_ix, storage);
std::vector<uint8_t> lit_depth(256);
std::vector<uint16_t> lit_bits(256);
std::vector<uint8_t> cmd_depth(kNumCommandPrefixes);
std::vector<uint16_t> cmd_bits(kNumCommandPrefixes);
std::vector<uint8_t> dist_depth(64);
std::vector<uint16_t> dist_bits(64);
HuffmanTree* tree = static_cast<HuffmanTree*>(
malloc(kMaxHuffmanTreeSize * sizeof(HuffmanTree)));
BuildAndStoreHuffmanTree(&lit_histo.data_[0], 256, tree,
&lit_depth[0], &lit_bits[0],
storage_ix, storage);
BuildAndStoreHuffmanTree(&cmd_histo.data_[0], kNumCommandPrefixes, tree,
&cmd_depth[0], &cmd_bits[0],
storage_ix, storage);
BuildAndStoreHuffmanTree(&dist_histo.data_[0], 64, tree,
&dist_depth[0], &dist_bits[0],
storage_ix, storage);
free(tree);
StoreDataWithHuffmanCodes(input, start_pos, mask, commands,
n_commands, &lit_depth[0], &lit_bits[0],
&cmd_depth[0], &cmd_bits[0],
&dist_depth[0], &dist_bits[0],
storage_ix, storage);
if (is_last) {
JumpToByteBoundary(storage_ix, storage);
}
}
void StoreMetaBlockFast(const uint8_t* input,
size_t start_pos,
size_t length,
size_t mask,
bool is_last,
const brotli::Command *commands,
size_t n_commands,
size_t *storage_ix,
uint8_t *storage) {
StoreCompressedMetaBlockHeader(is_last, length, storage_ix, storage);
WriteBits(13, 0, storage_ix, storage);
if (n_commands <= 128) {
uint32_t histogram[256] = { 0 };
size_t pos = start_pos;
size_t num_literals = 0;
for (size_t i = 0; i < n_commands; ++i) {
const Command cmd = commands[i];
for (size_t j = cmd.insert_len_; j != 0; --j) {
++histogram[input[pos & mask]];
++pos;
}
num_literals += cmd.insert_len_;
pos += cmd.copy_len();
}
uint8_t lit_depth[256] = { 0 };
uint16_t lit_bits[256] = { 0 };
BuildAndStoreHuffmanTreeFast(histogram, num_literals,
/* max_bits = */ 8,
lit_depth, lit_bits,
storage_ix, storage);
StoreStaticCommandHuffmanTree(storage_ix, storage);
StoreStaticDistanceHuffmanTree(storage_ix, storage);
StoreDataWithHuffmanCodes(input, start_pos, mask, commands,
n_commands, &lit_depth[0], &lit_bits[0],
kStaticCommandCodeDepth,
kStaticCommandCodeBits,
kStaticDistanceCodeDepth,
kStaticDistanceCodeBits,
storage_ix, storage);
} else {
HistogramLiteral lit_histo;
HistogramCommand cmd_histo;
HistogramDistance dist_histo;
BuildHistograms(input, start_pos, mask, commands, n_commands,
&lit_histo, &cmd_histo, &dist_histo);
std::vector<uint8_t> lit_depth(256);
std::vector<uint16_t> lit_bits(256);
std::vector<uint8_t> cmd_depth(kNumCommandPrefixes);
std::vector<uint16_t> cmd_bits(kNumCommandPrefixes);
std::vector<uint8_t> dist_depth(64);
std::vector<uint16_t> dist_bits(64);
BuildAndStoreHuffmanTreeFast(&lit_histo.data_[0], lit_histo.total_count_,
/* max_bits = */ 8,
&lit_depth[0], &lit_bits[0],
storage_ix, storage);
BuildAndStoreHuffmanTreeFast(&cmd_histo.data_[0], cmd_histo.total_count_,
/* max_bits = */ 10,
&cmd_depth[0], &cmd_bits[0],
storage_ix, storage);
BuildAndStoreHuffmanTreeFast(&dist_histo.data_[0], dist_histo.total_count_,
/* max_bits = */ 6,
&dist_depth[0], &dist_bits[0],
storage_ix, storage);
StoreDataWithHuffmanCodes(input, start_pos, mask, commands,
n_commands, &lit_depth[0], &lit_bits[0],
&cmd_depth[0], &cmd_bits[0],
&dist_depth[0], &dist_bits[0],
storage_ix, storage);
}
if (is_last) {
JumpToByteBoundary(storage_ix, storage);
}
}
/* This is for storing uncompressed blocks (simple raw storage of
bytes-as-bytes). */
void StoreUncompressedMetaBlock(bool final_block,
const uint8_t * __restrict input,
size_t position, size_t mask,
size_t len,
size_t * __restrict storage_ix,
uint8_t * __restrict storage) {
StoreUncompressedMetaBlockHeader(len, storage_ix, storage);
JumpToByteBoundary(storage_ix, storage);
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 BrotliWriteBits. */
brotli::WriteBitsPrepareStorage(*storage_ix, storage);
/* Since the uncompressed 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 */
JumpToByteBoundary(storage_ix, storage);
}
}
void StoreSyncMetaBlock(size_t * __restrict storage_ix,
uint8_t * __restrict storage) {
// Empty metadata meta-block bit pattern:
// 1 bit: is_last (0)
// 2 bits: num nibbles (3)
// 1 bit: reserved (0)
// 2 bits: metadata length bytes (0)
WriteBits(6, 6, storage_ix, storage);
JumpToByteBoundary(storage_ix, storage);
}
} // namespace brotli
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