| /* Copyright 2015 Google Inc. All Rights Reserved. |
| |
| Distributed under MIT license. |
| See file LICENSE for detail or copy at https://opensource.org/licenses/MIT |
| */ |
| |
| /* Algorithms for distributing the literals and commands of a metablock between |
| block types and contexts. */ |
| |
| #include "./metablock.h" |
| |
| #include "../common/constants.h" |
| #include "../common/platform.h" |
| #include <brotli/types.h> |
| #include "./bit_cost.h" |
| #include "./block_splitter.h" |
| #include "./cluster.h" |
| #include "./context.h" |
| #include "./entropy_encode.h" |
| #include "./histogram.h" |
| #include "./memory.h" |
| #include "./quality.h" |
| |
| #if defined(__cplusplus) || defined(c_plusplus) |
| extern "C" { |
| #endif |
| |
| void BrotliBuildMetaBlock(MemoryManager* m, |
| const uint8_t* ringbuffer, |
| const size_t pos, |
| const size_t mask, |
| const BrotliEncoderParams* params, |
| uint8_t prev_byte, |
| uint8_t prev_byte2, |
| const Command* cmds, |
| size_t num_commands, |
| ContextType literal_context_mode, |
| MetaBlockSplit* mb) { |
| /* Histogram ids need to fit in one byte. */ |
| static const size_t kMaxNumberOfHistograms = 256; |
| HistogramDistance* distance_histograms; |
| HistogramLiteral* literal_histograms; |
| ContextType* literal_context_modes = NULL; |
| size_t literal_histograms_size; |
| size_t distance_histograms_size; |
| size_t i; |
| size_t literal_context_multiplier = 1; |
| |
| BrotliSplitBlock(m, cmds, num_commands, |
| ringbuffer, pos, mask, params, |
| &mb->literal_split, |
| &mb->command_split, |
| &mb->distance_split); |
| if (BROTLI_IS_OOM(m)) return; |
| |
| if (!params->disable_literal_context_modeling) { |
| literal_context_multiplier = 1 << BROTLI_LITERAL_CONTEXT_BITS; |
| literal_context_modes = |
| BROTLI_ALLOC(m, ContextType, mb->literal_split.num_types); |
| if (BROTLI_IS_OOM(m)) return; |
| for (i = 0; i < mb->literal_split.num_types; ++i) { |
| literal_context_modes[i] = literal_context_mode; |
| } |
| } |
| |
| literal_histograms_size = |
| mb->literal_split.num_types * literal_context_multiplier; |
| literal_histograms = |
| BROTLI_ALLOC(m, HistogramLiteral, literal_histograms_size); |
| if (BROTLI_IS_OOM(m)) return; |
| ClearHistogramsLiteral(literal_histograms, literal_histograms_size); |
| |
| distance_histograms_size = |
| mb->distance_split.num_types << BROTLI_DISTANCE_CONTEXT_BITS; |
| distance_histograms = |
| BROTLI_ALLOC(m, HistogramDistance, distance_histograms_size); |
| if (BROTLI_IS_OOM(m)) return; |
| ClearHistogramsDistance(distance_histograms, distance_histograms_size); |
| |
| BROTLI_DCHECK(mb->command_histograms == 0); |
| mb->command_histograms_size = mb->command_split.num_types; |
| mb->command_histograms = |
| BROTLI_ALLOC(m, HistogramCommand, mb->command_histograms_size); |
| if (BROTLI_IS_OOM(m)) return; |
| ClearHistogramsCommand(mb->command_histograms, mb->command_histograms_size); |
| |
| BrotliBuildHistogramsWithContext(cmds, num_commands, |
| &mb->literal_split, &mb->command_split, &mb->distance_split, |
| ringbuffer, pos, mask, prev_byte, prev_byte2, literal_context_modes, |
| literal_histograms, mb->command_histograms, distance_histograms); |
| BROTLI_FREE(m, literal_context_modes); |
| |
| BROTLI_DCHECK(mb->literal_context_map == 0); |
| mb->literal_context_map_size = |
| mb->literal_split.num_types << BROTLI_LITERAL_CONTEXT_BITS; |
| mb->literal_context_map = |
| BROTLI_ALLOC(m, uint32_t, mb->literal_context_map_size); |
| if (BROTLI_IS_OOM(m)) return; |
| |
| BROTLI_DCHECK(mb->literal_histograms == 0); |
| mb->literal_histograms_size = mb->literal_context_map_size; |
| mb->literal_histograms = |
| BROTLI_ALLOC(m, HistogramLiteral, mb->literal_histograms_size); |
| if (BROTLI_IS_OOM(m)) return; |
| |
| BrotliClusterHistogramsLiteral(m, literal_histograms, literal_histograms_size, |
| kMaxNumberOfHistograms, mb->literal_histograms, |
| &mb->literal_histograms_size, mb->literal_context_map); |
| if (BROTLI_IS_OOM(m)) return; |
| BROTLI_FREE(m, literal_histograms); |
| |
| if (params->disable_literal_context_modeling) { |
| /* Distribute assignment to all contexts. */ |
| for (i = mb->literal_split.num_types; i != 0;) { |
| size_t j = 0; |
| i--; |
| for (; j < (1 << BROTLI_LITERAL_CONTEXT_BITS); j++) { |
| mb->literal_context_map[(i << BROTLI_LITERAL_CONTEXT_BITS) + j] = |
| mb->literal_context_map[i]; |
| } |
| } |
| } |
| |
| BROTLI_DCHECK(mb->distance_context_map == 0); |
| mb->distance_context_map_size = |
| mb->distance_split.num_types << BROTLI_DISTANCE_CONTEXT_BITS; |
| mb->distance_context_map = |
| BROTLI_ALLOC(m, uint32_t, mb->distance_context_map_size); |
| if (BROTLI_IS_OOM(m)) return; |
| |
| BROTLI_DCHECK(mb->distance_histograms == 0); |
| mb->distance_histograms_size = mb->distance_context_map_size; |
| mb->distance_histograms = |
| BROTLI_ALLOC(m, HistogramDistance, mb->distance_histograms_size); |
| if (BROTLI_IS_OOM(m)) return; |
| |
| BrotliClusterHistogramsDistance(m, distance_histograms, |
| mb->distance_context_map_size, |
| kMaxNumberOfHistograms, |
| mb->distance_histograms, |
| &mb->distance_histograms_size, |
| mb->distance_context_map); |
| if (BROTLI_IS_OOM(m)) return; |
| BROTLI_FREE(m, distance_histograms); |
| } |
| |
| #define FN(X) X ## Literal |
| #include "./metablock_inc.h" /* NOLINT(build/include) */ |
| #undef FN |
| |
| #define FN(X) X ## Command |
| #include "./metablock_inc.h" /* NOLINT(build/include) */ |
| #undef FN |
| |
| #define FN(X) X ## Distance |
| #include "./metablock_inc.h" /* NOLINT(build/include) */ |
| #undef FN |
| |
| #define BROTLI_MAX_STATIC_CONTEXTS 13 |
| |
| /* Greedy block splitter for one block category (literal, command or distance). |
| Gathers histograms for all context buckets. */ |
| typedef struct ContextBlockSplitter { |
| /* Alphabet size of particular block category. */ |
| size_t alphabet_size_; |
| size_t num_contexts_; |
| size_t max_block_types_; |
| /* We collect at least this many symbols for each block. */ |
| size_t min_block_size_; |
| /* We merge histograms A and B if |
| entropy(A+B) < entropy(A) + entropy(B) + split_threshold_, |
| where A is the current histogram and B is the histogram of the last or the |
| second last block type. */ |
| double split_threshold_; |
| |
| size_t num_blocks_; |
| BlockSplit* split_; /* not owned */ |
| HistogramLiteral* histograms_; /* not owned */ |
| size_t* histograms_size_; /* not owned */ |
| |
| /* The number of symbols that we want to collect before deciding on whether |
| or not to merge the block with a previous one or emit a new block. */ |
| size_t target_block_size_; |
| /* The number of symbols in the current histogram. */ |
| size_t block_size_; |
| /* Offset of the current histogram. */ |
| size_t curr_histogram_ix_; |
| /* Offset of the histograms of the previous two block types. */ |
| size_t last_histogram_ix_[2]; |
| /* Entropy of the previous two block types. */ |
| double last_entropy_[2 * BROTLI_MAX_STATIC_CONTEXTS]; |
| /* The number of times we merged the current block with the last one. */ |
| size_t merge_last_count_; |
| } ContextBlockSplitter; |
| |
| static void InitContextBlockSplitter( |
| MemoryManager* m, ContextBlockSplitter* self, size_t alphabet_size, |
| size_t num_contexts, size_t min_block_size, double split_threshold, |
| size_t num_symbols, BlockSplit* split, HistogramLiteral** histograms, |
| size_t* histograms_size) { |
| size_t max_num_blocks = num_symbols / min_block_size + 1; |
| size_t max_num_types; |
| BROTLI_DCHECK(num_contexts <= BROTLI_MAX_STATIC_CONTEXTS); |
| |
| self->alphabet_size_ = alphabet_size; |
| self->num_contexts_ = num_contexts; |
| self->max_block_types_ = BROTLI_MAX_NUMBER_OF_BLOCK_TYPES / num_contexts; |
| self->min_block_size_ = min_block_size; |
| self->split_threshold_ = split_threshold; |
| self->num_blocks_ = 0; |
| self->split_ = split; |
| self->histograms_size_ = histograms_size; |
| self->target_block_size_ = min_block_size; |
| self->block_size_ = 0; |
| self->curr_histogram_ix_ = 0; |
| self->merge_last_count_ = 0; |
| |
| /* We have to allocate one more histogram than the maximum number of block |
| types for the current histogram when the meta-block is too big. */ |
| max_num_types = |
| BROTLI_MIN(size_t, max_num_blocks, self->max_block_types_ + 1); |
| BROTLI_ENSURE_CAPACITY(m, uint8_t, |
| split->types, split->types_alloc_size, max_num_blocks); |
| BROTLI_ENSURE_CAPACITY(m, uint32_t, |
| split->lengths, split->lengths_alloc_size, max_num_blocks); |
| if (BROTLI_IS_OOM(m)) return; |
| split->num_blocks = max_num_blocks; |
| if (BROTLI_IS_OOM(m)) return; |
| BROTLI_DCHECK(*histograms == 0); |
| *histograms_size = max_num_types * num_contexts; |
| *histograms = BROTLI_ALLOC(m, HistogramLiteral, *histograms_size); |
| self->histograms_ = *histograms; |
| if (BROTLI_IS_OOM(m)) return; |
| /* Clear only current histogram. */ |
| ClearHistogramsLiteral(&self->histograms_[0], num_contexts); |
| self->last_histogram_ix_[0] = self->last_histogram_ix_[1] = 0; |
| } |
| |
| /* Does either of three things: |
| (1) emits the current block with a new block type; |
| (2) emits the current block with the type of the second last block; |
| (3) merges the current block with the last block. */ |
| static void ContextBlockSplitterFinishBlock( |
| ContextBlockSplitter* self, MemoryManager* m, BROTLI_BOOL is_final) { |
| BlockSplit* split = self->split_; |
| const size_t num_contexts = self->num_contexts_; |
| double* last_entropy = self->last_entropy_; |
| HistogramLiteral* histograms = self->histograms_; |
| |
| if (self->block_size_ < self->min_block_size_) { |
| self->block_size_ = self->min_block_size_; |
| } |
| if (self->num_blocks_ == 0) { |
| size_t i; |
| /* Create first block. */ |
| split->lengths[0] = (uint32_t)self->block_size_; |
| split->types[0] = 0; |
| |
| for (i = 0; i < num_contexts; ++i) { |
| last_entropy[i] = |
| BitsEntropy(histograms[i].data_, self->alphabet_size_); |
| last_entropy[num_contexts + i] = last_entropy[i]; |
| } |
| ++self->num_blocks_; |
| ++split->num_types; |
| self->curr_histogram_ix_ += num_contexts; |
| if (self->curr_histogram_ix_ < *self->histograms_size_) { |
| ClearHistogramsLiteral( |
| &self->histograms_[self->curr_histogram_ix_], self->num_contexts_); |
| } |
| self->block_size_ = 0; |
| } else if (self->block_size_ > 0) { |
| /* Try merging the set of histograms for the current block type with the |
| respective set of histograms for the last and second last block types. |
| Decide over the split based on the total reduction of entropy across |
| all contexts. */ |
| double entropy[BROTLI_MAX_STATIC_CONTEXTS]; |
| HistogramLiteral* combined_histo = |
| BROTLI_ALLOC(m, HistogramLiteral, 2 * num_contexts); |
| double combined_entropy[2 * BROTLI_MAX_STATIC_CONTEXTS]; |
| double diff[2] = { 0.0 }; |
| size_t i; |
| if (BROTLI_IS_OOM(m)) return; |
| for (i = 0; i < num_contexts; ++i) { |
| size_t curr_histo_ix = self->curr_histogram_ix_ + i; |
| size_t j; |
| entropy[i] = BitsEntropy(histograms[curr_histo_ix].data_, |
| self->alphabet_size_); |
| for (j = 0; j < 2; ++j) { |
| size_t jx = j * num_contexts + i; |
| size_t last_histogram_ix = self->last_histogram_ix_[j] + i; |
| combined_histo[jx] = histograms[curr_histo_ix]; |
| HistogramAddHistogramLiteral(&combined_histo[jx], |
| &histograms[last_histogram_ix]); |
| combined_entropy[jx] = BitsEntropy( |
| &combined_histo[jx].data_[0], self->alphabet_size_); |
| diff[j] += combined_entropy[jx] - entropy[i] - last_entropy[jx]; |
| } |
| } |
| |
| if (split->num_types < self->max_block_types_ && |
| diff[0] > self->split_threshold_ && |
| diff[1] > self->split_threshold_) { |
| /* Create new block. */ |
| split->lengths[self->num_blocks_] = (uint32_t)self->block_size_; |
| split->types[self->num_blocks_] = (uint8_t)split->num_types; |
| self->last_histogram_ix_[1] = self->last_histogram_ix_[0]; |
| self->last_histogram_ix_[0] = split->num_types * num_contexts; |
| for (i = 0; i < num_contexts; ++i) { |
| last_entropy[num_contexts + i] = last_entropy[i]; |
| last_entropy[i] = entropy[i]; |
| } |
| ++self->num_blocks_; |
| ++split->num_types; |
| self->curr_histogram_ix_ += num_contexts; |
| if (self->curr_histogram_ix_ < *self->histograms_size_) { |
| ClearHistogramsLiteral( |
| &self->histograms_[self->curr_histogram_ix_], self->num_contexts_); |
| } |
| self->block_size_ = 0; |
| self->merge_last_count_ = 0; |
| self->target_block_size_ = self->min_block_size_; |
| } else if (diff[1] < diff[0] - 20.0) { |
| /* Combine this block with second last block. */ |
| split->lengths[self->num_blocks_] = (uint32_t)self->block_size_; |
| split->types[self->num_blocks_] = split->types[self->num_blocks_ - 2]; |
| BROTLI_SWAP(size_t, self->last_histogram_ix_, 0, 1); |
| for (i = 0; i < num_contexts; ++i) { |
| histograms[self->last_histogram_ix_[0] + i] = |
| combined_histo[num_contexts + i]; |
| last_entropy[num_contexts + i] = last_entropy[i]; |
| last_entropy[i] = combined_entropy[num_contexts + i]; |
| HistogramClearLiteral(&histograms[self->curr_histogram_ix_ + i]); |
| } |
| ++self->num_blocks_; |
| self->block_size_ = 0; |
| self->merge_last_count_ = 0; |
| self->target_block_size_ = self->min_block_size_; |
| } else { |
| /* Combine this block with last block. */ |
| split->lengths[self->num_blocks_ - 1] += (uint32_t)self->block_size_; |
| for (i = 0; i < num_contexts; ++i) { |
| histograms[self->last_histogram_ix_[0] + i] = combined_histo[i]; |
| last_entropy[i] = combined_entropy[i]; |
| if (split->num_types == 1) { |
| last_entropy[num_contexts + i] = last_entropy[i]; |
| } |
| HistogramClearLiteral(&histograms[self->curr_histogram_ix_ + i]); |
| } |
| self->block_size_ = 0; |
| if (++self->merge_last_count_ > 1) { |
| self->target_block_size_ += self->min_block_size_; |
| } |
| } |
| BROTLI_FREE(m, combined_histo); |
| } |
| if (is_final) { |
| *self->histograms_size_ = split->num_types * num_contexts; |
| split->num_blocks = self->num_blocks_; |
| } |
| } |
| |
| /* Adds the next symbol to the current block type and context. When the |
| current block reaches the target size, decides on merging the block. */ |
| static void ContextBlockSplitterAddSymbol( |
| ContextBlockSplitter* self, MemoryManager* m, |
| size_t symbol, size_t context) { |
| HistogramAddLiteral(&self->histograms_[self->curr_histogram_ix_ + context], |
| symbol); |
| ++self->block_size_; |
| if (self->block_size_ == self->target_block_size_) { |
| ContextBlockSplitterFinishBlock(self, m, /* is_final = */ BROTLI_FALSE); |
| if (BROTLI_IS_OOM(m)) return; |
| } |
| } |
| |
| static void MapStaticContexts(MemoryManager* m, |
| size_t num_contexts, |
| const uint32_t* static_context_map, |
| MetaBlockSplit* mb) { |
| size_t i; |
| BROTLI_DCHECK(mb->literal_context_map == 0); |
| mb->literal_context_map_size = |
| mb->literal_split.num_types << BROTLI_LITERAL_CONTEXT_BITS; |
| mb->literal_context_map = |
| BROTLI_ALLOC(m, uint32_t, mb->literal_context_map_size); |
| if (BROTLI_IS_OOM(m)) return; |
| |
| for (i = 0; i < mb->literal_split.num_types; ++i) { |
| uint32_t offset = (uint32_t)(i * num_contexts); |
| size_t j; |
| for (j = 0; j < (1u << BROTLI_LITERAL_CONTEXT_BITS); ++j) { |
| mb->literal_context_map[(i << BROTLI_LITERAL_CONTEXT_BITS) + j] = |
| offset + static_context_map[j]; |
| } |
| } |
| } |
| |
| static BROTLI_INLINE void BrotliBuildMetaBlockGreedyInternal( |
| MemoryManager* m, const uint8_t* ringbuffer, size_t pos, size_t mask, |
| uint8_t prev_byte, uint8_t prev_byte2, ContextType literal_context_mode, |
| const size_t num_contexts, const uint32_t* static_context_map, |
| const Command *commands, size_t n_commands, MetaBlockSplit* mb) { |
| union { |
| BlockSplitterLiteral plain; |
| ContextBlockSplitter ctx; |
| } lit_blocks; |
| BlockSplitterCommand cmd_blocks; |
| BlockSplitterDistance dist_blocks; |
| size_t num_literals = 0; |
| size_t i; |
| for (i = 0; i < n_commands; ++i) { |
| num_literals += commands[i].insert_len_; |
| } |
| |
| if (num_contexts == 1) { |
| InitBlockSplitterLiteral(m, &lit_blocks.plain, 256, 512, 400.0, |
| num_literals, &mb->literal_split, &mb->literal_histograms, |
| &mb->literal_histograms_size); |
| } else { |
| InitContextBlockSplitter(m, &lit_blocks.ctx, 256, num_contexts, 512, 400.0, |
| num_literals, &mb->literal_split, &mb->literal_histograms, |
| &mb->literal_histograms_size); |
| } |
| if (BROTLI_IS_OOM(m)) return; |
| InitBlockSplitterCommand(m, &cmd_blocks, BROTLI_NUM_COMMAND_SYMBOLS, 1024, |
| 500.0, n_commands, &mb->command_split, &mb->command_histograms, |
| &mb->command_histograms_size); |
| if (BROTLI_IS_OOM(m)) return; |
| InitBlockSplitterDistance(m, &dist_blocks, 64, 512, 100.0, n_commands, |
| &mb->distance_split, &mb->distance_histograms, |
| &mb->distance_histograms_size); |
| if (BROTLI_IS_OOM(m)) return; |
| |
| for (i = 0; i < n_commands; ++i) { |
| const Command cmd = commands[i]; |
| size_t j; |
| BlockSplitterAddSymbolCommand(&cmd_blocks, cmd.cmd_prefix_); |
| for (j = cmd.insert_len_; j != 0; --j) { |
| uint8_t literal = ringbuffer[pos & mask]; |
| if (num_contexts == 1) { |
| BlockSplitterAddSymbolLiteral(&lit_blocks.plain, literal); |
| } else { |
| size_t context = Context(prev_byte, prev_byte2, literal_context_mode); |
| ContextBlockSplitterAddSymbol(&lit_blocks.ctx, m, literal, |
| static_context_map[context]); |
| if (BROTLI_IS_OOM(m)) return; |
| } |
| prev_byte2 = prev_byte; |
| prev_byte = literal; |
| ++pos; |
| } |
| pos += CommandCopyLen(&cmd); |
| if (CommandCopyLen(&cmd)) { |
| prev_byte2 = ringbuffer[(pos - 2) & mask]; |
| prev_byte = ringbuffer[(pos - 1) & mask]; |
| if (cmd.cmd_prefix_ >= 128) { |
| BlockSplitterAddSymbolDistance(&dist_blocks, cmd.dist_prefix_); |
| } |
| } |
| } |
| |
| if (num_contexts == 1) { |
| BlockSplitterFinishBlockLiteral( |
| &lit_blocks.plain, /* is_final = */ BROTLI_TRUE); |
| } else { |
| ContextBlockSplitterFinishBlock( |
| &lit_blocks.ctx, m, /* is_final = */ BROTLI_TRUE); |
| if (BROTLI_IS_OOM(m)) return; |
| } |
| BlockSplitterFinishBlockCommand(&cmd_blocks, /* is_final = */ BROTLI_TRUE); |
| BlockSplitterFinishBlockDistance(&dist_blocks, /* is_final = */ BROTLI_TRUE); |
| |
| if (num_contexts > 1) { |
| MapStaticContexts(m, num_contexts, static_context_map, mb); |
| } |
| } |
| |
| void BrotliBuildMetaBlockGreedy(MemoryManager* m, |
| const uint8_t* ringbuffer, |
| size_t pos, |
| size_t mask, |
| uint8_t prev_byte, |
| uint8_t prev_byte2, |
| ContextType literal_context_mode, |
| size_t num_contexts, |
| const uint32_t* static_context_map, |
| const Command* commands, |
| size_t n_commands, |
| MetaBlockSplit* mb) { |
| if (num_contexts == 1) { |
| BrotliBuildMetaBlockGreedyInternal(m, ringbuffer, pos, mask, prev_byte, |
| prev_byte2, literal_context_mode, 1, NULL, commands, n_commands, mb); |
| } else { |
| BrotliBuildMetaBlockGreedyInternal(m, ringbuffer, pos, mask, prev_byte, |
| prev_byte2, literal_context_mode, num_contexts, static_context_map, |
| commands, n_commands, mb); |
| } |
| } |
| |
| void BrotliOptimizeHistograms(size_t num_direct_distance_codes, |
| size_t distance_postfix_bits, |
| MetaBlockSplit* mb) { |
| uint8_t good_for_rle[BROTLI_NUM_COMMAND_SYMBOLS]; |
| size_t num_distance_codes; |
| size_t i; |
| for (i = 0; i < mb->literal_histograms_size; ++i) { |
| BrotliOptimizeHuffmanCountsForRle(256, mb->literal_histograms[i].data_, |
| good_for_rle); |
| } |
| for (i = 0; i < mb->command_histograms_size; ++i) { |
| BrotliOptimizeHuffmanCountsForRle(BROTLI_NUM_COMMAND_SYMBOLS, |
| mb->command_histograms[i].data_, |
| good_for_rle); |
| } |
| num_distance_codes = BROTLI_NUM_DISTANCE_SHORT_CODES + |
| num_direct_distance_codes + |
| ((2 * BROTLI_MAX_DISTANCE_BITS) << distance_postfix_bits); |
| for (i = 0; i < mb->distance_histograms_size; ++i) { |
| BrotliOptimizeHuffmanCountsForRle(num_distance_codes, |
| mb->distance_histograms[i].data_, |
| good_for_rle); |
| } |
| } |
| |
| #if defined(__cplusplus) || defined(c_plusplus) |
| } /* extern "C" */ |
| #endif |
