kc3-lang/brotli/enc/encode.cc

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• Hash : d2e857d8
  Author :
  Date : 2015-10-23T11:19:04
  

  Fix integer overflow and slowness in entropy estimation.
  

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• enc/encode.cc

• // Copyright 2013 Google Inc. All Rights Reserved.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  // http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  //
  // Implementation of Brotli compressor.
  
  #include "./encode.h"
  
  #include <algorithm>
  #include <limits>
  
  #include "./backward_references.h"
  #include "./bit_cost.h"
  #include "./block_splitter.h"
  #include "./brotli_bit_stream.h"
  #include "./cluster.h"
  #include "./context.h"
  #include "./metablock.h"
  #include "./transform.h"
  #include "./entropy_encode.h"
  #include "./fast_log.h"
  #include "./hash.h"
  #include "./histogram.h"
  #include "./prefix.h"
  #include "./utf8_util.h"
  #include "./write_bits.h"
  
  namespace brotli {
  
  static const int kMinQualityForBlockSplit = 4;
  static const int kMinQualityForContextModeling = 5;
  static const int kMinQualityForOptimizeHistograms = 4;
  // For quality 1 there is no block splitting, so we buffer at most this much
  // literals and commands.
  static const int kMaxNumDelayedSymbols = 0x2fff;
  
  void RecomputeDistancePrefixes(Command* cmds,
                                 size_t num_commands,
                                 int num_direct_distance_codes,
                                 int distance_postfix_bits) {
    if (num_direct_distance_codes == 0 && distance_postfix_bits == 0) {
      return;
    }
    for (int i = 0; i < num_commands; ++i) {
      Command* cmd = &cmds[i];
      if (cmd->copy_len_ > 0 && cmd->cmd_prefix_ >= 128) {
        PrefixEncodeCopyDistance(cmd->DistanceCode(),
                                 num_direct_distance_codes,
                                 distance_postfix_bits,
                                 &cmd->dist_prefix_,
                                 &cmd->dist_extra_);
      }
    }
  }
  
  uint8_t* BrotliCompressor::GetBrotliStorage(size_t size) {
    if (storage_size_ < size) {
      delete[] storage_;
      storage_ = new uint8_t[size];
      storage_size_ = size;
    }
    return storage_;
  }
  
  BrotliCompressor::BrotliCompressor(BrotliParams params)
      : params_(params),
        hashers_(new Hashers()),
        input_pos_(0),
        num_commands_(0),
        num_literals_(0),
        last_insert_len_(0),
        last_flush_pos_(0),
        last_processed_pos_(0),
        prev_byte_(0),
        prev_byte2_(0),
        storage_size_(0),
        storage_(0) {
    // Sanitize params.
    params_.quality = std::max(1, params_.quality);
    if (params_.lgwin < kMinWindowBits) {
      params_.lgwin = kMinWindowBits;
    } else if (params_.lgwin > kMaxWindowBits) {
      params_.lgwin = kMaxWindowBits;
    }
    if (params_.lgblock == 0) {
      params_.lgblock = params_.quality < kMinQualityForBlockSplit ? 14 : 16;
      if (params_.quality >= 9 && params_.lgwin > params_.lgblock) {
        params_.lgblock = std::min(21, params_.lgwin);
      }
    } else {
      params_.lgblock = std::min(kMaxInputBlockBits,
                                 std::max(kMinInputBlockBits, params_.lgblock));
    }
  
    // Set maximum distance, see section 9.1. of the spec.
    max_backward_distance_ = (1 << params_.lgwin) - 16;
  
    // Initialize input and literal cost ring buffers.
    // We allocate at least lgwin + 1 bits for the ring buffer so that the newly
    // added block fits there completely and we still get lgwin bits and at least
    // read_block_size_bits + 1 bits because the copy tail length needs to be
    // smaller than ringbuffer size.
    int ringbuffer_bits = std::max(params_.lgwin + 1, params_.lgblock + 1);
    ringbuffer_ = new RingBuffer(ringbuffer_bits, params_.lgblock);
  
    commands_ = 0;
    cmd_alloc_size_ = 0;
  
    // Initialize last byte with stream header.
    if (params_.lgwin == 16) {
      last_byte_ = 0;
      last_byte_bits_ = 1;
    } else if (params_.lgwin == 17) {
      last_byte_ = 1;
      last_byte_bits_ = 7;
    } else if (params_.lgwin > 17) {
      last_byte_ = ((params_.lgwin - 17) << 1) | 1;
      last_byte_bits_ = 4;
    } else {
      last_byte_ = ((params_.lgwin - 8) << 4) | 1;
      last_byte_bits_ = 7;
    }
  
    // Initialize distance cache.
    dist_cache_[0] = 4;
    dist_cache_[1] = 11;
    dist_cache_[2] = 15;
    dist_cache_[3] = 16;
    // Save the state of the distance cache in case we need to restore it for
    // emitting an uncompressed block.
    memcpy(saved_dist_cache_, dist_cache_, sizeof(dist_cache_));
  
    // Initialize hashers.
    hash_type_ = std::min(9, params_.quality);
    hashers_->Init(hash_type_);
  }
  
  BrotliCompressor::~BrotliCompressor() {
    delete[] storage_;
    free(commands_);
    delete ringbuffer_;
    delete hashers_;
  }
  
  void BrotliCompressor::CopyInputToRingBuffer(const size_t input_size,
                                               const uint8_t* input_buffer) {
    ringbuffer_->Write(input_buffer, input_size);
    input_pos_ += input_size;
  
    // TL;DR: If needed, initialize 7 more bytes in the ring buffer to make the
    // hashing not depend on uninitialized data. This makes compression
    // deterministic and it prevents uninitialized memory warnings in Valgrind.
    // Even without erasing, the output would be valid (but nondeterministic).
    //
    // Background information: The compressor stores short (at most 8 bytes)
    // substrings of the input already read in a hash table, and detects
    // repetitions by looking up such substrings in the hash table. If it
    // can find a substring, it checks whether the substring is really there
    // in the ring buffer (or it's just a hash collision). Should the hash
    // table become corrupt, this check makes sure that the output is
    // still valid, albeit the compression ratio would be bad.
    //
    // The compressor populates the hash table from the ring buffer as it's
    // reading new bytes from the input. However, at the last few indexes of
    // the ring buffer, there are not enough bytes to build full-length
    // substrings from. Since the hash table always contains full-length
    // substrings, we erase with dummy 0s here to make sure that those
    // substrings will contain 0s at the end instead of uninitialized
    // data.
    //
    // Please note that erasing is not necessary (because the
    // memory region is already initialized since he ring buffer
    // has a `tail' that holds a copy of the beginning,) so we
    // skip erasing if we have already gone around at least once in
    // the ring buffer.
    size_t pos = ringbuffer_->position();
    // Only clear during the first round of ringbuffer writes. On
    // subsequent rounds data in the ringbuffer would be affected.
    if (pos <= ringbuffer_->mask()) {
      // This is the first time when the ring buffer is being written.
      // We clear 7 bytes just after the bytes that have been copied from
      // the input buffer.
      //
      // The ringbuffer has a "tail" that holds a copy of the beginning,
      // but only once the ring buffer has been fully written once, i.e.,
      // pos <= mask. For the first time, we need to write values
      // in this tail (where index may be larger than mask), so that
      // we have exactly defined behavior and don't read un-initialized
      // memory. Due to performance reasons, hashing reads data using a
      // LOAD64, which can go 7 bytes beyond the bytes written in the
      // ringbuffer.
      memset(ringbuffer_->start() + pos, 0, 7);
    }
  }
  
  void BrotliCompressor::BrotliSetCustomDictionary(
      const size_t size, const uint8_t* dict) {
    CopyInputToRingBuffer(size, dict);
    last_flush_pos_ = size;
    last_processed_pos_ = size;
    if (size > 0) {
      prev_byte_ = dict[size - 1];
    }
    if (size > 1) {
      prev_byte2_ = dict[size - 2];
    }
    hashers_->PrependCustomDictionary(hash_type_, size, dict);
  }
  
  bool BrotliCompressor::WriteBrotliData(const bool is_last,
                                         const bool force_flush,
                                         size_t* out_size,
                                         uint8_t** output) {
    const size_t bytes = input_pos_ - last_processed_pos_;
    const uint8_t* data = ringbuffer_->start();
    const size_t mask = ringbuffer_->mask();
  
    if (bytes > input_block_size()) {
      return false;
    }
  
    // Theoretical max number of commands is 1 per 2 bytes.
    size_t newsize = num_commands_ + bytes / 2 + 1;
    if (newsize > cmd_alloc_size_) {
      // Reserve a bit more memory to allow merging with a next block
      // without realloc: that would impact speed.
      newsize += bytes / 4;
      cmd_alloc_size_ = newsize;
      commands_ =
          static_cast<Command*>(realloc(commands_, sizeof(Command) * newsize));
    }
  
    CreateBackwardReferences(bytes, last_processed_pos_, data, mask,
                             max_backward_distance_,
                             params_.quality,
                             hashers_,
                             hash_type_,
                             dist_cache_,
                             &last_insert_len_,
                             &commands_[num_commands_],
                             &num_commands_,
                             &num_literals_);
  
    int max_length = std::min<int>(mask + 1, 1 << kMaxInputBlockBits);
    if (!is_last && !force_flush &&
        (params_.quality >= kMinQualityForBlockSplit ||
         (num_literals_ + num_commands_ < kMaxNumDelayedSymbols)) &&
        input_pos_ + input_block_size() <= last_flush_pos_ + max_length) {
      // Merge with next input block. Everything will happen later.
      last_processed_pos_ = input_pos_;
      *out_size = 0;
      return true;
    }
  
    // Create the last insert-only command.
    if (last_insert_len_ > 0) {
      brotli::Command cmd(last_insert_len_);
      commands_[num_commands_++] = cmd;
      num_literals_ += last_insert_len_;
      last_insert_len_ = 0;
    }
  
    return WriteMetaBlockInternal(is_last, out_size, output);
  }
  
  // Decide about the context map based on the ability of the prediction
  // ability of the previous byte UTF8-prefix on the next byte. The
  // prediction ability is calculated as shannon entropy. Here we need
  // shannon entropy instead of 'BitsEntropy' since the prefix will be
  // encoded with the remaining 6 bits of the following byte, and
  // BitsEntropy will assume that symbol to be stored alone using Huffman
  // coding.
  void ChooseContextMap(int quality,
                        int* bigram_histo,
                        int* num_literal_contexts,
                        const int** literal_context_map) {
    int monogram_histo[3] = { 0 };
    int two_prefix_histo[6] = { 0 };
    int total = 0;
    for (int i = 0; i < 9; ++i) {
      total += bigram_histo[i];
      monogram_histo[i % 3] += bigram_histo[i];
      int j = i;
      if (j >= 6) {
        j -= 6;
      }
      two_prefix_histo[j] += bigram_histo[i];
    }
    int dummy;
    double entropy1 = ShannonEntropy(monogram_histo, 3, &dummy);
    double entropy2 = (ShannonEntropy(two_prefix_histo, 3, &dummy) +
                       ShannonEntropy(two_prefix_histo + 3, 3, &dummy));
    double entropy3 = 0;
    for (int k = 0; k < 3; ++k) {
      entropy3 += ShannonEntropy(bigram_histo + 3 * k, 3, &dummy);
    }
  
    assert(total != 0);
    entropy1 *= (1.0 / total);
    entropy2 *= (1.0 / total);
    entropy3 *= (1.0 / total);
  
    static const int kStaticContextMapContinuation[64] = {
      1, 1, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    };
    static const int kStaticContextMapSimpleUTF8[64] = {
      0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    };
    if (quality < 7) {
      // 3 context models is a bit slower, don't use it at lower qualities.
      entropy3 = entropy1 * 10;
    }
    // If expected savings by symbol are less than 0.2 bits, skip the
    // context modeling -- in exchange for faster decoding speed.
    if (entropy1 - entropy2 < 0.2 &&
        entropy1 - entropy3 < 0.2) {
      *num_literal_contexts = 1;
    } else if (entropy2 - entropy3 < 0.02) {
      *num_literal_contexts = 2;
      *literal_context_map = kStaticContextMapSimpleUTF8;
    } else {
      *num_literal_contexts = 3;
      *literal_context_map = kStaticContextMapContinuation;
    }
  }
  
  void DecideOverLiteralContextModeling(const uint8_t* input,
                                        size_t start_pos,
                                        size_t length,
                                        size_t mask,
                                        int quality,
                                        int* literal_context_mode,
                                        int* num_literal_contexts,
                                        const int** literal_context_map) {
    if (quality < kMinQualityForContextModeling || length < 64) {
      return;
    }
    // Gather bigram data of the UTF8 byte prefixes. To make the analysis of
    // UTF8 data faster we only examine 64 byte long strides at every 4kB
    // intervals.
    const size_t end_pos = start_pos + length;
    int bigram_prefix_histo[9] = { 0 };
    for (; start_pos + 64 <= end_pos; start_pos += 4096) {
        static const int lut[4] = { 0, 0, 1, 2 };
      const size_t stride_end_pos = start_pos + 64;
      int prev = lut[input[start_pos & mask] >> 6] * 3;
      for (size_t pos = start_pos + 1; pos < stride_end_pos; ++pos) {
        const uint8_t literal = input[pos & mask];
        ++bigram_prefix_histo[prev + lut[literal >> 6]];
        prev = lut[literal >> 6] * 3;
      }
    }
    *literal_context_mode = CONTEXT_UTF8;
    ChooseContextMap(quality, &bigram_prefix_histo[0], num_literal_contexts,
                     literal_context_map);
  }
  
  bool BrotliCompressor::WriteMetaBlockInternal(const bool is_last,
                                                size_t* out_size,
                                                uint8_t** output) {
    const size_t bytes = input_pos_ - last_flush_pos_;
    const uint8_t* data = ringbuffer_->start();
    const size_t mask = ringbuffer_->mask();
    const size_t max_out_size = 2 * bytes + 500;
    uint8_t* storage = GetBrotliStorage(max_out_size);
    storage[0] = last_byte_;
    int storage_ix = last_byte_bits_;
  
    bool uncompressed = false;
    if (num_commands_ < (bytes >> 8) + 2) {
      if (num_literals_ > 0.99 * bytes) {
        int literal_histo[256] = { 0 };
        static const int kSampleRate = 13;
        static const double kMinEntropy = 7.92;
        const double bit_cost_threshold = bytes * kMinEntropy / kSampleRate;
        for (size_t i = last_flush_pos_; i < input_pos_; i += kSampleRate) {
          ++literal_histo[data[i & mask]];
        }
        if (BitsEntropy(literal_histo, 256) > bit_cost_threshold) {
          uncompressed = true;
        }
      }
    }
  
    if (bytes == 0) {
      if (!StoreCompressedMetaBlockHeader(is_last, 0, &storage_ix, &storage[0])) {
        return false;
      }
      storage_ix = (storage_ix + 7) & ~7;
    } else if (uncompressed) {
      // Restore the distance cache, as its last update by
      // CreateBackwardReferences is now unused.
      memcpy(dist_cache_, saved_dist_cache_, sizeof(dist_cache_));
      if (!StoreUncompressedMetaBlock(is_last,
                                      data, last_flush_pos_, mask, bytes,
                                      &storage_ix,
                                      &storage[0])) {
        return false;
      }
    } else {
      int num_direct_distance_codes = 0;
      int distance_postfix_bits = 0;
      if (params_.quality > 9 && params_.mode == BrotliParams::MODE_FONT) {
        num_direct_distance_codes = 12;
        distance_postfix_bits = 1;
        RecomputeDistancePrefixes(commands_,
                                  num_commands_,
                                  num_direct_distance_codes,
                                  distance_postfix_bits);
      }
      if (params_.quality < kMinQualityForBlockSplit) {
        if (!StoreMetaBlockTrivial(data, last_flush_pos_, bytes, mask, is_last,
                                   commands_, num_commands_,
                                   &storage_ix,
                                   &storage[0])) {
          return false;
        }
      } else {
        MetaBlockSplit mb;
        int literal_context_mode = CONTEXT_UTF8;
        if (params_.quality <= 9) {
          int num_literal_contexts = 1;
          const int* literal_context_map = NULL;
          DecideOverLiteralContextModeling(data, last_flush_pos_, bytes, mask,
                                           params_.quality,
                                           &literal_context_mode,
                                           &num_literal_contexts,
                                           &literal_context_map);
          if (literal_context_map == NULL) {
            BuildMetaBlockGreedy(data, last_flush_pos_, mask,
                                 commands_, num_commands_,
                                 &mb);
          } else {
            BuildMetaBlockGreedyWithContexts(data, last_flush_pos_, mask,
                                             prev_byte_, prev_byte2_,
                                             literal_context_mode,
                                             num_literal_contexts,
                                             literal_context_map,
                                             commands_, num_commands_,
                                             &mb);
          }
        } else {
          if (!IsMostlyUTF8(data, last_flush_pos_, mask, bytes, kMinUTF8Ratio)) {
            literal_context_mode = CONTEXT_SIGNED;
          }
          BuildMetaBlock(data, last_flush_pos_, mask,
                         prev_byte_, prev_byte2_,
                         commands_, num_commands_,
                         literal_context_mode,
                         &mb);
        }
        if (params_.quality >= kMinQualityForOptimizeHistograms) {
          OptimizeHistograms(num_direct_distance_codes,
                             distance_postfix_bits,
                             &mb);
        }
        if (!StoreMetaBlock(data, last_flush_pos_, bytes, mask,
                            prev_byte_, prev_byte2_,
                            is_last,
                            num_direct_distance_codes,
                            distance_postfix_bits,
                            literal_context_mode,
                            commands_, num_commands_,
                            mb,
                            &storage_ix,
                            &storage[0])) {
          return false;
        }
      }
      if (bytes + 4 < (storage_ix >> 3)) {
        // Restore the distance cache and last byte.
        memcpy(dist_cache_, saved_dist_cache_, sizeof(dist_cache_));
        storage[0] = last_byte_;
        storage_ix = last_byte_bits_;
        if (!StoreUncompressedMetaBlock(is_last, data, last_flush_pos_, mask,
                                        bytes, &storage_ix, &storage[0])) {
          return false;
        }
      }
    }
    last_byte_ = storage[storage_ix >> 3];
    last_byte_bits_ = storage_ix & 7;
    last_flush_pos_ = input_pos_;
    last_processed_pos_ = input_pos_;
    prev_byte_ = data[(last_flush_pos_ - 1) & mask];
    prev_byte2_ = data[(last_flush_pos_ - 2) & mask];
    num_commands_ = 0;
    num_literals_ = 0;
    // Save the state of the distance cache in case we need to restore it for
    // emitting an uncompressed block.
    memcpy(saved_dist_cache_, dist_cache_, sizeof(dist_cache_));
    *output = &storage[0];
    *out_size = storage_ix >> 3;
    return true;
  }
  
  bool BrotliCompressor::WriteMetaBlock(const size_t input_size,
                                        const uint8_t* input_buffer,
                                        const bool is_last,
                                        size_t* encoded_size,
                                        uint8_t* encoded_buffer) {
    CopyInputToRingBuffer(input_size, input_buffer);
    size_t out_size = 0;
    uint8_t* output;
    if (!WriteBrotliData(is_last, /* force_flush = */ true, &out_size, &output) ||
        out_size > *encoded_size) {
      return false;
    }
    if (out_size > 0) {
      memcpy(encoded_buffer, output, out_size);
    }
    *encoded_size = out_size;
    return true;
  }
  
  bool BrotliCompressor::WriteMetadata(const size_t input_size,
                                       const uint8_t* input_buffer,
                                       const bool is_last,
                                       size_t* encoded_size,
                                       uint8_t* encoded_buffer) {
    if (input_size > (1 << 24) || input_size + 6 > *encoded_size) {
      return false;
    }
    int storage_ix = last_byte_bits_;
    encoded_buffer[0] = last_byte_;
    WriteBits(1, 0, &storage_ix, encoded_buffer);
    WriteBits(2, 3, &storage_ix, encoded_buffer);
    WriteBits(1, 0, &storage_ix, encoded_buffer);
    if (input_size == 0) {
      WriteBits(2, 0, &storage_ix, encoded_buffer);
      *encoded_size = (storage_ix + 7) >> 3;
    } else {
      size_t nbits = Log2Floor(input_size - 1) + 1;
      size_t nbytes = (nbits + 7) / 8;
      WriteBits(2, nbytes, &storage_ix, encoded_buffer);
      WriteBits(8 * nbytes, input_size - 1, &storage_ix, encoded_buffer);
      size_t hdr_size = (storage_ix + 7) >> 3;
      memcpy(&encoded_buffer[hdr_size], input_buffer, input_size);
      *encoded_size = hdr_size + input_size;
    }
    if (is_last) {
      encoded_buffer[(*encoded_size)++] = 3;
    }
    last_byte_ = 0;
    last_byte_bits_ = 0;
    return true;
  }
  
  bool BrotliCompressor::FinishStream(
      size_t* encoded_size, uint8_t* encoded_buffer) {
    return WriteMetaBlock(0, NULL, true, encoded_size, encoded_buffer);
  }
  
  int BrotliCompressBuffer(BrotliParams params,
                           size_t input_size,
                           const uint8_t* input_buffer,
                           size_t* encoded_size,
                           uint8_t* encoded_buffer) {
    if (*encoded_size == 0) {
      // Output buffer needs at least one byte.
      return 0;
    }
    BrotliMemIn in(input_buffer, input_size);
    BrotliMemOut out(encoded_buffer, *encoded_size);
    if (!BrotliCompress(params, &in, &out)) {
      return 0;
    }
    *encoded_size = out.position();
    return 1;
  }
  
  size_t CopyOneBlockToRingBuffer(BrotliIn* r, BrotliCompressor* compressor) {
    const size_t block_size = compressor->input_block_size();
    size_t bytes_read = 0;
    const uint8_t* data = reinterpret_cast<const uint8_t*>(
        r->Read(block_size, &bytes_read));
    if (data == NULL) {
      return 0;
    }
    compressor->CopyInputToRingBuffer(bytes_read, data);
  
    // Read more bytes until block_size is filled or an EOF (data == NULL) is
    // received. This is useful to get deterministic compressed output for the
    // same input no matter how r->Read splits the input to chunks.
    for (size_t remaining = block_size - bytes_read; remaining > 0; ) {
      size_t more_bytes_read = 0;
      data = reinterpret_cast<const uint8_t*>(
          r->Read(remaining, &more_bytes_read));
      if (data == NULL) {
        break;
      }
      compressor->CopyInputToRingBuffer(more_bytes_read, data);
      bytes_read += more_bytes_read;
      remaining -= more_bytes_read;
    }
    return bytes_read;
  }
  
  bool BrotliInIsFinished(BrotliIn* r) {
    size_t read_bytes;
    return r->Read(0, &read_bytes) == NULL;
  }
  
  int BrotliCompress(BrotliParams params, BrotliIn* in, BrotliOut* out) {
    return BrotliCompressWithCustomDictionary(0, 0, params, in, out);
  }
  
  int BrotliCompressWithCustomDictionary(size_t dictsize, const uint8_t* dict,
                                         BrotliParams params,
                                         BrotliIn* in, BrotliOut* out) {
    size_t in_bytes = 0;
    size_t out_bytes = 0;
    uint8_t* output;
    bool final_block = false;
    BrotliCompressor compressor(params);
    if (dictsize != 0) compressor.BrotliSetCustomDictionary(dictsize, dict);
    while (!final_block) {
      in_bytes = CopyOneBlockToRingBuffer(in, &compressor);
      final_block = in_bytes == 0 || BrotliInIsFinished(in);
      out_bytes = 0;
      if (!compressor.WriteBrotliData(final_block,
                                      /* force_flush = */ false,
                                      &out_bytes, &output)) {
        return false;
      }
      if (out_bytes > 0 && !out->Write(output, out_bytes)) {
        return false;
      }
    }
    return true;
  }
  
  
  }  // namespace brotli
  

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