1 files changed, 183 insertions, 0 deletions
diff --git a/modules/brotli/enc/metablock_inc.h b/modules/brotli/enc/metablock_inc.h
new file mode 100644
index 0000000000..dcc9d3c4a6
--- /dev/null
+++ b/modules/brotli/enc/metablock_inc.h
@@ -0,0 +1,183 @@
+/* NOLINT(build/header_guard) */
+/* Copyright 2015 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+/* template parameters: FN */
+
+#define HistogramType FN(Histogram)
+
+/* Greedy block splitter for one block category (literal, command or distance).
+*/
+typedef struct FN(BlockSplitter) {
+  /* Alphabet size of particular block category. */
+  size_t alphabet_size_;
+  /* 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 */
+  HistogramType* 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];
+  /* The number of times we merged the current block with the last one. */
+  size_t merge_last_count_;
+} FN(BlockSplitter);
+
+static void FN(InitBlockSplitter)(
+    MemoryManager* m, FN(BlockSplitter)* self, size_t alphabet_size,
+    size_t min_block_size, double split_threshold, size_t num_symbols,
+    BlockSplit* split, HistogramType** histograms, size_t* histograms_size) {
+  size_t max_num_blocks = num_symbols / min_block_size + 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. */
+  size_t max_num_types =
+      BROTLI_MIN(size_t, max_num_blocks, BROTLI_MAX_NUMBER_OF_BLOCK_TYPES + 1);
+  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(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;
+  self->split_->num_blocks = max_num_blocks;
+  BROTLI_DCHECK(*histograms == 0);
+  *histograms_size = max_num_types;
+  *histograms = BROTLI_ALLOC(m, HistogramType, *histograms_size);
+  self->histograms_ = *histograms;
+  if (BROTLI_IS_OOM(m)) return;
+  /* Clear only current histogram. */
+  FN(HistogramClear)(&self->histograms_[0]);
+  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 FN(BlockSplitterFinishBlock)(
+    FN(BlockSplitter)* self, BROTLI_BOOL is_final) {
+  BlockSplit* split = self->split_;
+  double* last_entropy = self->last_entropy_;
+  HistogramType* histograms = 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_t)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_)
+      FN(HistogramClear)(&histograms[self->curr_histogram_ix_]);
+    self->block_size_ = 0;
+  } else if (self->block_size_ > 0) {
+    double entropy = BitsEntropy(histograms[self->curr_histogram_ix_].data_,
+                                 self->alphabet_size_);
+    HistogramType combined_histo[2];
+    double combined_entropy[2];
+    double diff[2];
+    size_t j;
+    for (j = 0; j < 2; ++j) {
+      size_t last_histogram_ix = self->last_histogram_ix_[j];
+      combined_histo[j] = histograms[self->curr_histogram_ix_];
+      FN(HistogramAddHistogram)(&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 < BROTLI_MAX_NUMBER_OF_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] = (uint8_t)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_)
+        FN(HistogramClear)(&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) {
+      /* 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);
+      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;
+      FN(HistogramClear)(&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_t)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;
+      FN(HistogramClear)(&histograms[self->curr_histogram_ix_]);
+      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. */
+static void FN(BlockSplitterAddSymbol)(FN(BlockSplitter)* self, size_t symbol) {
+  FN(HistogramAdd)(&self->histograms_[self->curr_histogram_ix_], symbol);
+  ++self->block_size_;
+  if (self->block_size_ == self->target_block_size_) {
+    FN(BlockSplitterFinishBlock)(self, /* is_final = */ BROTLI_FALSE);
+  }
+}
+
+#undef HistogramType