Added brotli enc/ and tools/ directories.

third_party/brotli/enc/block_splitter.cc

+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+// Block split point selection utilities.
+
+#include "./block_splitter.h"
+
+#include <assert.h>
+#include <math.h>
+
+#include <algorithm>
+#include <cstring>
+#include <vector>
+
+#include "./cluster.h"
+#include "./command.h"
+#include "./fast_log.h"
+#include "./histogram.h"
+
+namespace brotli {
+
+static const size_t kMaxLiteralHistograms = 100;
+static const size_t kMaxCommandHistograms = 50;
+static const double kLiteralBlockSwitchCost = 28.1;
+static const double kCommandBlockSwitchCost = 13.5;
+static const double kDistanceBlockSwitchCost = 14.6;
+static const size_t kLiteralStrideLength = 70;
+static const size_t kCommandStrideLength = 40;
+static const size_t kSymbolsPerLiteralHistogram = 544;
+static const size_t kSymbolsPerCommandHistogram = 530;
+static const size_t kSymbolsPerDistanceHistogram = 544;
+static const size_t kMinLengthForBlockSplitting = 128;
+static const size_t kIterMulForRefining = 2;
+static const size_t kMinItersForRefining = 100;
+
+void CopyLiteralsToByteArray(const Command* cmds,
+                             const size_t num_commands,
+                             const uint8_t* data,
+                             const size_t offset,
+                             const size_t mask,
+                             std::vector<uint8_t>* literals) {
+  // Count how many we have.
+  size_t total_length = 0;
+  for (size_t i = 0; i < num_commands; ++i) {
+    total_length += cmds[i].insert_len_;
+  }
+  if (total_length == 0) {
+    return;
+  }
+
+  // Allocate.
+  literals->resize(total_length);
+
+  // Loop again, and copy this time.
+  size_t pos = 0;
+  size_t from_pos = offset & mask;
+  for (size_t i = 0; i < num_commands && pos < total_length; ++i) {
+    size_t insert_len = cmds[i].insert_len_;
+    if (from_pos + insert_len > mask) {
+      size_t head_size = mask + 1 - from_pos;
+      memcpy(&(*literals)[pos], data + from_pos, head_size);
+      from_pos = 0;
+      pos += head_size;
+      insert_len -= head_size;
+    }
+    if (insert_len > 0) {
+      memcpy(&(*literals)[pos], data + from_pos, insert_len);
+      pos += insert_len;
+    }
+    from_pos = (from_pos + insert_len + cmds[i].copy_len()) & mask;
+  }
+}
+
+inline static unsigned int MyRand(unsigned int* seed) {
+  *seed *= 16807U;
+  if (*seed == 0) {
+    *seed = 1;
+  }
+  return *seed;
+}
+
+template<typename HistogramType, typename DataType>
+void InitialEntropyCodes(const DataType* data, size_t length,
+                         size_t stride,
+                         size_t num_histograms,
+                         HistogramType* histograms) {
+  for (size_t i = 0; i < num_histograms; ++i) {
+    histograms[i].Clear();
+  }
+  unsigned int seed = 7;
+  size_t block_length = length / num_histograms;
+  for (size_t i = 0; i < num_histograms; ++i) {
+    size_t pos = length * i / num_histograms;
+    if (i != 0) {
+      pos += MyRand(&seed) % block_length;
+    }
+    if (pos + stride >= length) {
+      pos = length - stride - 1;
+    }
+    histograms[i].Add(data + pos, stride);
+  }
+}
+
+template<typename HistogramType, typename DataType>
+void RandomSample(unsigned int* seed,
+                  const DataType* data,
+                  size_t length,
+                  size_t stride,
+                  HistogramType* sample) {
+  size_t pos = 0;
+  if (stride >= length) {
+    pos = 0;
+    stride = length;
+  } else {
+    pos = MyRand(seed) % (length - stride + 1);
+  }
+  sample->Add(data + pos, stride);
+}
+
+template<typename HistogramType, typename DataType>
+void RefineEntropyCodes(const DataType* data, size_t length,
+                        size_t stride,
+                        size_t num_histograms,
+                        HistogramType* histograms) {
+  size_t iters =
+      kIterMulForRefining * length / stride + kMinItersForRefining;
+  unsigned int seed = 7;
+  iters = ((iters + num_histograms - 1) / num_histograms) * num_histograms;
+  for (size_t iter = 0; iter < iters; ++iter) {
+    HistogramType sample;
+    RandomSample(&seed, data, length, stride, &sample);
+    size_t ix = iter % num_histograms;
+    histograms[ix].AddHistogram(sample);
+  }
+}
+
+inline static double BitCost(size_t count) {
+  return count == 0 ? -2.0 : FastLog2(count);
+}
+
+// Assigns a block id from the range [0, vec.size()) to each data element
+// in data[0..length) and fills in block_id[0..length) with the assigned values.
+// Returns the number of blocks, i.e. one plus the number of block switches.
+template<typename DataType, int kSize>
+size_t FindBlocks(const DataType* data, const size_t length,
+                  const double block_switch_bitcost,
+                  const size_t num_histograms,
+                  const Histogram<kSize>* histograms,
+                  double* insert_cost,
+                  double* cost,
+                  uint8_t* switch_signal,
+                  uint8_t *block_id) {
+  if (num_histograms <= 1) {
+    for (size_t i = 0; i < length; ++i) {
+      block_id[i] = 0;
+    }
+    return 1;
+  }
+  const size_t bitmaplen = (num_histograms + 7) >> 3;
+  assert(num_histograms <= 256);
+  memset(insert_cost, 0, sizeof(insert_cost[0]) * kSize * num_histograms);
+  for (size_t j = 0; j < num_histograms; ++j) {
+    insert_cost[j] = FastLog2(static_cast<uint32_t>(
+        histograms[j].total_count_));
+  }
+  for (size_t i = kSize; i != 0;) {
+    --i;
+    for (size_t j = 0; j < num_histograms; ++j) {
+      insert_cost[i * num_histograms + j] =
+          insert_cost[j] - BitCost(histograms[j].data_[i]);
+    }
+  }
+  memset(cost, 0, sizeof(cost[0]) * num_histograms);
+  memset(switch_signal, 0, sizeof(switch_signal[0]) * length * bitmaplen);
+  // After each iteration of this loop, cost[k] will contain the difference
+  // between the minimum cost of arriving at the current byte position using
+  // entropy code k, and the minimum cost of arriving at the current byte
+  // position. This difference is capped at the block switch cost, and if it
+  // reaches block switch cost, it means that when we trace back from the last
+  // position, we need to switch here.
+  for (size_t byte_ix = 0; byte_ix < length; ++byte_ix) {
+    size_t ix = byte_ix * bitmaplen;
+    size_t insert_cost_ix = data[byte_ix] * num_histograms;
+    double min_cost = 1e99;
+    for (size_t k = 0; k < num_histograms; ++k) {
+      // We are coding the symbol in data[byte_ix] with entropy code k.
+      cost[k] += insert_cost[insert_cost_ix + k];
+      if (cost[k] < min_cost) {
+        min_cost = cost[k];
+        block_id[byte_ix] = static_cast<uint8_t>(k);
+      }
+    }
+    double block_switch_cost = block_switch_bitcost;
+    // More blocks for the beginning.
+    if (byte_ix < 2000) {
+      block_switch_cost *= 0.77 + 0.07 * static_cast<double>(byte_ix) / 2000;
+    }
+    for (size_t k = 0; k < num_histograms; ++k) {
+      cost[k] -= min_cost;
+      if (cost[k] >= block_switch_cost) {
+        cost[k] = block_switch_cost;
+        const uint8_t mask = static_cast<uint8_t>(1u << (k & 7));
+        assert((k >> 3) < bitmaplen);
+        switch_signal[ix + (k >> 3)] |= mask;
+      }
+    }
+  }
+  // Now trace back from the last position and switch at the marked places.
+  size_t byte_ix = length - 1;
+  size_t ix = byte_ix * bitmaplen;
+  uint8_t cur_id = block_id[byte_ix];
+  size_t num_blocks = 1;
+  while (byte_ix > 0) {
+    --byte_ix;
+    ix -= bitmaplen;
+    const uint8_t mask = static_cast<uint8_t>(1u << (cur_id & 7));
+    assert((static_cast<size_t>(cur_id) >> 3) < bitmaplen);
+    if (switch_signal[ix + (cur_id >> 3)] & mask) {
+      if (cur_id != block_id[byte_ix]) {
+        cur_id = block_id[byte_ix];
+        ++num_blocks;
+      }
+    }
+    block_id[byte_ix] = cur_id;
+  }
+  return num_blocks;
+}
+
+static size_t RemapBlockIds(uint8_t* block_ids, const size_t length,
+                            uint16_t* new_id, const size_t num_histograms) {
+  static const uint16_t kInvalidId = 256;
+  for (size_t i = 0; i < num_histograms; ++i) {
+    new_id[i] = kInvalidId;
+  }
+  uint16_t next_id = 0;
+  for (size_t i = 0; i < length; ++i) {
+    assert(block_ids[i] < num_histograms);
+    if (new_id[block_ids[i]] == kInvalidId) {
+      new_id[block_ids[i]] = next_id++;
+    }
+  }
+  for (size_t i = 0; i < length; ++i) {
+    block_ids[i] = static_cast<uint8_t>(new_id[block_ids[i]]);
+    assert(block_ids[i] < num_histograms);
+  }
+  assert(next_id <= num_histograms);
+  return next_id;
+}
+
+template<typename HistogramType, typename DataType>
+void BuildBlockHistograms(const DataType* data, const size_t length,
+                          const uint8_t* block_ids,
+                          const size_t num_histograms,
+                          HistogramType* histograms) {
+  for (size_t i = 0; i < num_histograms; ++i) {
+    histograms[i].Clear();
+  }
+  for (size_t i = 0; i < length; ++i) {
+    histograms[block_ids[i]].Add(data[i]);
+  }
+}
+
+template<typename HistogramType, typename DataType>
+void ClusterBlocks(const DataType* data, const size_t length,
+                   const size_t num_blocks,
+                   uint8_t* block_ids,
+                   BlockSplit* split) {
+  static const size_t kMaxNumberOfBlockTypes = 256;
+  static const size_t kHistogramsPerBatch = 64;
+  static const size_t kClustersPerBatch = 16;
+  std::vector<uint32_t> histogram_symbols(num_blocks);
+  std::vector<uint32_t> block_lengths(num_blocks);
+
+  size_t block_idx = 0;
+  for (size_t i = 0; i < length; ++i) {
+    assert(block_idx < num_blocks);
+    ++block_lengths[block_idx];
+    if (i + 1 == length || block_ids[i] != block_ids[i + 1]) {
+      ++block_idx;
+    }
+  }
+  assert(block_idx == num_blocks);
+
+  const size_t expected_num_clusters =
+      kClustersPerBatch *
+      (num_blocks + kHistogramsPerBatch - 1) / kHistogramsPerBatch;
+  std::vector<HistogramType> all_histograms;
+  std::vector<uint32_t> cluster_size;
+  all_histograms.reserve(expected_num_clusters);
+  cluster_size.reserve(expected_num_clusters);
+  size_t num_clusters = 0;
+  std::vector<HistogramType> histograms(
+      std::min(num_blocks, kHistogramsPerBatch));
+  size_t max_num_pairs = kHistogramsPerBatch * kHistogramsPerBatch / 2;
+  std::vector<HistogramPair> pairs(max_num_pairs + 1);
+  size_t pos = 0;
+  for (size_t i = 0; i < num_blocks; i += kHistogramsPerBatch) {
+    const size_t num_to_combine = std::min(num_blocks - i, kHistogramsPerBatch);
+    uint32_t sizes[kHistogramsPerBatch];
+    uint32_t clusters[kHistogramsPerBatch];
+    uint32_t symbols[kHistogramsPerBatch];
+    uint32_t remap[kHistogramsPerBatch];
+    for (size_t j = 0; j < num_to_combine; ++j) {
+      histograms[j].Clear();
+      for (size_t k = 0; k < block_lengths[i + j]; ++k) {
+        histograms[j].Add(data[pos++]);
+      }
+      histograms[j].bit_cost_ = PopulationCost(histograms[j]);
+      symbols[j] = clusters[j] = static_cast<uint32_t>(j);
+      sizes[j] = 1;
+    }
+    size_t num_new_clusters = HistogramCombine(
+        &histograms[0], sizes, symbols, clusters, &pairs[0], num_to_combine,
+        num_to_combine, kHistogramsPerBatch, max_num_pairs);
+    for (size_t j = 0; j < num_new_clusters; ++j) {
+      all_histograms.push_back(histograms[clusters[j]]);
+      cluster_size.push_back(sizes[clusters[j]]);
+      remap[clusters[j]] = static_cast<uint32_t>(j);
+    }
+    for (size_t j = 0; j < num_to_combine; ++j) {
+      histogram_symbols[i + j] =
+          static_cast<uint32_t>(num_clusters) + remap[symbols[j]];
+    }
+    num_clusters += num_new_clusters;
+    assert(num_clusters == cluster_size.size());
+    assert(num_clusters == all_histograms.size());
+  }
+
+  max_num_pairs =
+      std::min(64 * num_clusters, (num_clusters / 2) * num_clusters);
+  pairs.resize(max_num_pairs + 1);
+
+  std::vector<uint32_t> clusters(num_clusters);
+  for (size_t i = 0; i < num_clusters; ++i) {
+    clusters[i] = static_cast<uint32_t>(i);
+  }
+  size_t num_final_clusters =
+      HistogramCombine(&all_histograms[0], &cluster_size[0],
+                       &histogram_symbols[0],
+                       &clusters[0], &pairs[0], num_clusters,
+                       num_blocks, kMaxNumberOfBlockTypes, max_num_pairs);
+
+  static const uint32_t kInvalidIndex = std::numeric_limits<uint32_t>::max();
+  std::vector<uint32_t> new_index(num_clusters, kInvalidIndex);
+  uint32_t next_index = 0;
+  pos = 0;
+  for (size_t i = 0; i < num_blocks; ++i) {
+    HistogramType histo;
+    for (size_t j = 0; j < block_lengths[i]; ++j) {
+      histo.Add(data[pos++]);
+    }
+    uint32_t best_out =
+        i == 0 ? histogram_symbols[0] : histogram_symbols[i - 1];
+    double best_bits = HistogramBitCostDistance(
+        histo, all_histograms[best_out]);
+    for (size_t j = 0; j < num_final_clusters; ++j) {
+      const double cur_bits = HistogramBitCostDistance(
+          histo, all_histograms[clusters[j]]);
+      if (cur_bits < best_bits) {
+        best_bits = cur_bits;
+        best_out = clusters[j];
+      }
+    }
+    histogram_symbols[i] = best_out;
+    if (new_index[best_out] == kInvalidIndex) {
+      new_index[best_out] = next_index++;
+    }
+  }
+  uint8_t max_type = 0;
+  uint32_t cur_length = 0;
+  block_idx = 0;
+  split->types.resize(num_blocks);
+  split->lengths.resize(num_blocks);
+  for (size_t i = 0; i < num_blocks; ++i) {
+    cur_length += block_lengths[i];
+    if (i + 1 == num_blocks ||
+        histogram_symbols[i] != histogram_symbols[i + 1]) {
+      const uint8_t id = static_cast<uint8_t>(new_index[histogram_symbols[i]]);
+      split->types[block_idx] = id;
+      split->lengths[block_idx] = cur_length;
+      max_type = std::max(max_type, id);
+      cur_length = 0;
+      ++block_idx;
+    }
+  }
+  split->types.resize(block_idx);
+  split->lengths.resize(block_idx);
+  split->num_types = static_cast<size_t>(max_type) + 1;
+}
+
+template<int kSize, typename DataType>
+void SplitByteVector(const std::vector<DataType>& data,
+                     const size_t literals_per_histogram,
+                     const size_t max_histograms,
+                     const size_t sampling_stride_length,
+                     const double block_switch_cost,
+                     BlockSplit* split) {
+  if (data.empty()) {
+    split->num_types = 1;
+    return;
+  } else if (data.size() < kMinLengthForBlockSplitting) {
+    split->num_types = 1;
+    split->types.push_back(0);
+    split->lengths.push_back(static_cast<uint32_t>(data.size()));
+    return;
+  }
+  size_t num_histograms = data.size() / literals_per_histogram + 1;
+  if (num_histograms > max_histograms) {
+    num_histograms = max_histograms;
+  }
+  Histogram<kSize>* histograms = new Histogram<kSize>[num_histograms];
+  // Find good entropy codes.
+  InitialEntropyCodes(&data[0], data.size(),
+                      sampling_stride_length,
+                      num_histograms, histograms);
+  RefineEntropyCodes(&data[0], data.size(),
+                     sampling_stride_length,
+                     num_histograms, histograms);
+  // Find a good path through literals with the good entropy codes.
+  std::vector<uint8_t> block_ids(data.size());
+  size_t num_blocks;
+  const size_t bitmaplen = (num_histograms + 7) >> 3;
+  double* insert_cost = new double[kSize * num_histograms];
+  double *cost = new double[num_histograms];
+  uint8_t* switch_signal = new uint8_t[data.size() * bitmaplen];
+  uint16_t* new_id = new uint16_t[num_histograms];
+  for (size_t i = 0; i < 10; ++i) {
+    num_blocks = FindBlocks(&data[0], data.size(),
+                            block_switch_cost,
+                            num_histograms, histograms,
+                            insert_cost, cost, switch_signal,
+                            &block_ids[0]);
+    num_histograms = RemapBlockIds(&block_ids[0], data.size(),
+                                   new_id, num_histograms);
+    BuildBlockHistograms(&data[0], data.size(), &block_ids[0],
+                         num_histograms, histograms);
+  }
+  delete[] insert_cost;
+  delete[] cost;
+  delete[] switch_signal;
+  delete[] new_id;
+  delete[] histograms;
+  ClusterBlocks<Histogram<kSize> >(&data[0], data.size(), num_blocks,
+                                   &block_ids[0], split);
+}
+
+void SplitBlock(const Command* cmds,
+                const size_t num_commands,
+                const uint8_t* data,
+                const size_t pos,
+                const size_t mask,
+                BlockSplit* literal_split,
+                BlockSplit* insert_and_copy_split,
+                BlockSplit* dist_split) {
+  {
+    // Create a continuous array of literals.
+    std::vector<uint8_t> literals;
+    CopyLiteralsToByteArray(cmds, num_commands, data, pos, mask, &literals);
+    // Create the block split on the array of literals.
+    // Literal histograms have alphabet size 256.
+    SplitByteVector<256>(
+        literals,
+        kSymbolsPerLiteralHistogram, kMaxLiteralHistograms,
+        kLiteralStrideLength, kLiteralBlockSwitchCost,
+        literal_split);
+  }
+
+  {
+    // Compute prefix codes for commands.
+    std::vector<uint16_t> insert_and_copy_codes(num_commands);
+    for (size_t i = 0; i < num_commands; ++i) {
+      insert_and_copy_codes[i] = cmds[i].cmd_prefix_;
+    }
+    // Create the block split on the array of command prefixes.
+    SplitByteVector<kNumCommandPrefixes>(
+        insert_and_copy_codes,
+        kSymbolsPerCommandHistogram, kMaxCommandHistograms,
+        kCommandStrideLength, kCommandBlockSwitchCost,
+        insert_and_copy_split);
+  }
+
+  {
+    // Create a continuous array of distance prefixes.
+    std::vector<uint16_t> distance_prefixes(num_commands);
+    size_t pos = 0;
+    for (size_t i = 0; i < num_commands; ++i) {
+      const Command& cmd = cmds[i];
+      if (cmd.copy_len() && cmd.cmd_prefix_ >= 128) {
+        distance_prefixes[pos++] = cmd.dist_prefix_;
+      }
+    }
+    distance_prefixes.resize(pos);
+    // Create the block split on the array of distance prefixes.
+    SplitByteVector<kNumDistancePrefixes>(
+        distance_prefixes,
+        kSymbolsPerDistanceHistogram, kMaxCommandHistograms,
+        kCommandStrideLength, kDistanceBlockSwitchCost,
+        dist_split);
+  }
+}
+
+}  // namespace brotli