diff options
Diffstat (limited to 'vendor/github.com/andybalholm/brotli/metablock_command.go')
| -rw-r--r-- | vendor/github.com/andybalholm/brotli/metablock_command.go | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/vendor/github.com/andybalholm/brotli/metablock_command.go b/vendor/github.com/andybalholm/brotli/metablock_command.go new file mode 100644 index 0000000000..d47541c5e6 --- /dev/null +++ b/vendor/github.com/andybalholm/brotli/metablock_command.go @@ -0,0 +1,162 @@ +package brotli + +/* Copyright 2015 Google Inc. All Rights Reserved. + + Distributed under MIT license. + See file LICENSE for detail or copy at https://opensource.org/licenses/MIT +*/ + +/* Greedy block splitter for one block category (literal, command or distance). + */ +type blockSplitterCommand struct { + alphabet_size_ uint + min_block_size_ uint + split_threshold_ float64 + num_blocks_ uint + split_ *blockSplit + histograms_ []histogramCommand + histograms_size_ *uint + target_block_size_ uint + block_size_ uint + curr_histogram_ix_ uint + last_histogram_ix_ [2]uint + last_entropy_ [2]float64 + merge_last_count_ uint +} + +func initBlockSplitterCommand(self *blockSplitterCommand, alphabet_size uint, min_block_size uint, split_threshold float64, num_symbols uint, split *blockSplit, histograms *[]histogramCommand, histograms_size *uint) { + var max_num_blocks uint = num_symbols/min_block_size + 1 + var max_num_types uint = brotli_min_size_t(max_num_blocks, maxNumberOfBlockTypes+1) + /* 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. */ + self.alphabet_size_ = alphabet_size + + 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 + brotli_ensure_capacity_uint8_t(&split.types, &split.types_alloc_size, max_num_blocks) + brotli_ensure_capacity_uint32_t(&split.lengths, &split.lengths_alloc_size, max_num_blocks) + self.split_.num_blocks = max_num_blocks + assert(*histograms == nil) + *histograms_size = max_num_types + *histograms = make([]histogramCommand, (*histograms_size)) + self.histograms_ = *histograms + + /* Clear only current histogram. */ + histogramClearCommand(&self.histograms_[0]) + + self.last_histogram_ix_[1] = 0 + self.last_histogram_ix_[0] = self.last_histogram_ix_[1] +} + +/* 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. */ +func blockSplitterFinishBlockCommand(self *blockSplitterCommand, is_final bool) { + var split *blockSplit = self.split_ + var last_entropy []float64 = self.last_entropy_[:] + var histograms []histogramCommand = self.histograms_ + self.block_size_ = brotli_max_size_t(self.block_size_, self.min_block_size_) + if self.num_blocks_ == 0 { + /* Create first block. */ + split.lengths[0] = uint32(self.block_size_) + + split.types[0] = 0 + last_entropy[0] = bitsEntropy(histograms[0].data_[:], self.alphabet_size_) + last_entropy[1] = last_entropy[0] + self.num_blocks_++ + split.num_types++ + self.curr_histogram_ix_++ + if self.curr_histogram_ix_ < *self.histograms_size_ { + histogramClearCommand(&histograms[self.curr_histogram_ix_]) + } + self.block_size_ = 0 + } else if self.block_size_ > 0 { + var entropy float64 = bitsEntropy(histograms[self.curr_histogram_ix_].data_[:], self.alphabet_size_) + var combined_histo [2]histogramCommand + var combined_entropy [2]float64 + var diff [2]float64 + var j uint + for j = 0; j < 2; j++ { + var last_histogram_ix uint = self.last_histogram_ix_[j] + combined_histo[j] = histograms[self.curr_histogram_ix_] + histogramAddHistogramCommand(&combined_histo[j], &histograms[last_histogram_ix]) + combined_entropy[j] = bitsEntropy(combined_histo[j].data_[0:], self.alphabet_size_) + diff[j] = combined_entropy[j] - entropy - last_entropy[j] + } + + if split.num_types < maxNumberOfBlockTypes && diff[0] > self.split_threshold_ && diff[1] > self.split_threshold_ { + /* Create new block. */ + split.lengths[self.num_blocks_] = uint32(self.block_size_) + + split.types[self.num_blocks_] = byte(split.num_types) + self.last_histogram_ix_[1] = self.last_histogram_ix_[0] + self.last_histogram_ix_[0] = uint(byte(split.num_types)) + last_entropy[1] = last_entropy[0] + last_entropy[0] = entropy + self.num_blocks_++ + split.num_types++ + self.curr_histogram_ix_++ + if self.curr_histogram_ix_ < *self.histograms_size_ { + histogramClearCommand(&histograms[self.curr_histogram_ix_]) + } + 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 { + split.lengths[self.num_blocks_] = uint32(self.block_size_) + split.types[self.num_blocks_] = split.types[self.num_blocks_-2] + /* Combine this block with second last block. */ + + var tmp uint = self.last_histogram_ix_[0] + self.last_histogram_ix_[0] = self.last_histogram_ix_[1] + self.last_histogram_ix_[1] = tmp + histograms[self.last_histogram_ix_[0]] = combined_histo[1] + last_entropy[1] = last_entropy[0] + last_entropy[0] = combined_entropy[1] + self.num_blocks_++ + self.block_size_ = 0 + histogramClearCommand(&histograms[self.curr_histogram_ix_]) + 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(self.block_size_) + + histograms[self.last_histogram_ix_[0]] = combined_histo[0] + last_entropy[0] = combined_entropy[0] + if split.num_types == 1 { + last_entropy[1] = last_entropy[0] + } + + self.block_size_ = 0 + histogramClearCommand(&histograms[self.curr_histogram_ix_]) + self.merge_last_count_++ + if self.merge_last_count_ > 1 { + self.target_block_size_ += self.min_block_size_ + } + } + } + + if is_final { + *self.histograms_size_ = split.num_types + split.num_blocks = self.num_blocks_ + } +} + +/* Adds the next symbol to the current histogram. When the current histogram + reaches the target size, decides on merging the block. */ +func blockSplitterAddSymbolCommand(self *blockSplitterCommand, symbol uint) { + histogramAddCommand(&self.histograms_[self.curr_histogram_ix_], symbol) + self.block_size_++ + if self.block_size_ == self.target_block_size_ { + blockSplitterFinishBlockCommand(self, false) /* is_final = */ + } +} |