brotli/dec/decode.c

// 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.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "./bit_reader.h"
#include "./context.h"
#include "./decode.h"
#include "./huffman.h"
#include "./prefix.h"
#include "./safe_malloc.h"

#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif

#ifdef BROTLI_DECODE_DEBUG
#define BROTLI_LOG_UINT(name)                                    \
  printf("[%s] %s = %lu\n", __func__, #name, (unsigned long)(name))
#define BROTLI_LOG_ARRAY_INDEX(array_name, idx)                  \
  printf("[%s] %s[%lu] = %lu\n", __func__, #array_name, \
         (unsigned long)(idx), (unsigned long)array_name[idx])
#else
#define BROTLI_LOG_UINT(name)
#define BROTLI_LOG_ARRAY_INDEX(array_name, idx)
#endif

static const int kDefaultCodeLength = 8;
static const int kCodeLengthRepeatCode = 16;
static const int kNumLiteralCodes = 256;
static const int kNumInsertAndCopyCodes = 704;
static const int kNumBlockLengthCodes = 26;
static const int kLiteralContextBits = 6;
static const int kDistanceContextBits = 2;

#define CODE_LENGTH_CODES 18
static const uint8_t kCodeLengthCodeOrder[CODE_LENGTH_CODES] = {
  1, 2, 3, 4, 0, 17, 5, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15,
};

#define NUM_DISTANCE_SHORT_CODES 16
static const int kDistanceShortCodeIndexOffset[NUM_DISTANCE_SHORT_CODES] = {
  3, 2, 1, 0, 3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2
};

static const int kDistanceShortCodeValueOffset[NUM_DISTANCE_SHORT_CODES] = {
  0, 0, 0, 0, -1, 1, -2, 2, -3, 3, -1, 1, -2, 2, -3, 3
};

static BROTLI_INLINE int DecodeWindowBits(BrotliBitReader* br) {
  if (BrotliReadBits(br, 1)) {
    return 17 + BrotliReadBits(br, 3);
  } else {
    return 16;
  }
}

// Decodes a number in the range [0..255], by reading 1 - 11 bits.
static BROTLI_INLINE int DecodeVarLenUint8(BrotliBitReader* br) {
  if (BrotliReadBits(br, 1)) {
    int nbits = BrotliReadBits(br, 3);
    if (nbits == 0) {
      return 1;
    } else {
      return BrotliReadBits(br, nbits) + (1 << nbits);
    }
  }
  return 0;
}

static void DecodeMetaBlockLength(BrotliBitReader* br,
                                  size_t* meta_block_length,
                                  int* input_end,
                                  int* is_uncompressed) {
  *input_end = BrotliReadBits(br, 1);
  *meta_block_length = 0;
  *is_uncompressed = 0;
  if (*input_end && BrotliReadBits(br, 1)) {
    return;
  }
  int size_nibbles = BrotliReadBits(br, 2) + 4;
  int i;
  for (i = 0; i < size_nibbles; ++i) {
    *meta_block_length |= BrotliReadBits(br, 4) << (i * 4);
  }
  ++(*meta_block_length);
  if (!*input_end) {
    *is_uncompressed = BrotliReadBits(br, 1);
  }
}

// Decodes the next Huffman code from bit-stream.
static BROTLI_INLINE int ReadSymbol(const HuffmanTree* tree,
                                    BrotliBitReader* br) {
  const HuffmanTreeNode* node = tree->root_;
  BrotliFillBitWindow(br);
  uint32_t bits = BrotliPrefetchBits(br);
  int bitpos = br->bit_pos_;
  // Check if we find the bit combination from the Huffman lookup table.
  const int lut_ix = bits & (HUFF_LUT - 1);
  const int lut_bits = tree->lut_bits_[lut_ix];
  if (lut_bits <= HUFF_LUT_BITS) {
    BrotliSetBitPos(br, bitpos + lut_bits);
    return tree->lut_symbol_[lut_ix];
  }
  node += tree->lut_jump_[lut_ix];
  bitpos += HUFF_LUT_BITS;
  bits >>= HUFF_LUT_BITS;

  // Decode the value from a binary tree.
  assert(node != NULL);
  do {
    node = HuffmanTreeNextNode(node, bits & 1);
    bits >>= 1;
    ++bitpos;
  } while (HuffmanTreeNodeIsNotLeaf(node));
  BrotliSetBitPos(br, bitpos);
  return node->symbol_;
}

static void PrintUcharVector(const uint8_t* v, int len) {
  while (len-- > 0) printf(" %d", *v++);
  printf("\n");
}

static int ReadHuffmanCodeLengths(
    const uint8_t* code_length_code_lengths,
    int num_symbols, uint8_t* code_lengths,
    BrotliBitReader* br) {
  int ok = 0;
  int symbol;
  int max_symbol;
  int decode_number_of_code_length_codes;
  int prev_code_len = kDefaultCodeLength;
  int repeat = 0;
  int repeat_length = 0;
  HuffmanTree tree;

  if (!BrotliHuffmanTreeBuildImplicit(&tree, code_length_code_lengths,
                                      CODE_LENGTH_CODES)) {
    printf("[ReadHuffmanCodeLengths] Building code length tree failed: ");
    PrintUcharVector(code_length_code_lengths, CODE_LENGTH_CODES);
    return 0;
  }

  if (!BrotliReadMoreInput(br)) {
    printf("[ReadHuffmanCodeLengths] Unexpected end of input.\n");
    return 0;
  }
  decode_number_of_code_length_codes = BrotliReadBits(br, 1);
  BROTLI_LOG_UINT(decode_number_of_code_length_codes);
  if (decode_number_of_code_length_codes) {
    if (BrotliReadBits(br, 1)) {
      max_symbol = 68 + BrotliReadBits(br, 7);
    } else {
      max_symbol = 4 + BrotliReadBits(br, 6);
    }
    if (max_symbol > num_symbols) {
      printf("[ReadHuffmanCodeLengths] max_symbol > num_symbols (%d vs %d)\n",
             max_symbol, num_symbols);
      goto End;
    }
  } else {
    max_symbol = num_symbols;
  }
  BROTLI_LOG_UINT(max_symbol);

  symbol = 0;
  while (symbol + repeat < num_symbols) {
    int code_len;
    if (max_symbol-- == 0) break;
    if (!BrotliReadMoreInput(br)) {
      printf("[ReadHuffmanCodeLengths] Unexpected end of input.\n");
      goto End;
    }
    code_len = ReadSymbol(&tree, br);
    BROTLI_LOG_UINT(symbol);
    BROTLI_LOG_UINT(repeat);
    BROTLI_LOG_UINT(repeat_length);
    BROTLI_LOG_UINT(code_len);
    if ((code_len < kCodeLengthRepeatCode) ||
        (code_len == kCodeLengthRepeatCode && repeat_length == 0) ||
        (code_len > kCodeLengthRepeatCode && repeat_length > 0)) {
      while (repeat > 0) {
        code_lengths[symbol++] = repeat_length;
        --repeat;
      }
    }
    if (code_len < kCodeLengthRepeatCode) {
      code_lengths[symbol++] = code_len;
      if (code_len != 0) prev_code_len = code_len;
    } else {
      const int extra_bits = code_len - 14;
      if (repeat > 0) {
        repeat -= 2;
        repeat <<= extra_bits;
      }
      repeat += BrotliReadBits(br, extra_bits) + 3;
      repeat_length = (code_len == kCodeLengthRepeatCode ? prev_code_len : 0);
    }
  }
  if (symbol + repeat > num_symbols) {
    printf("[ReadHuffmanCodeLengths] symbol + repeat > num_symbols "
           "(%d + %d vs %d)\n", symbol, repeat, num_symbols);
    goto End;
  }
  while (repeat-- > 0) code_lengths[symbol++] = repeat_length;
  while (symbol < num_symbols) code_lengths[symbol++] = 0;
  ok = 1;

 End:
  BrotliHuffmanTreeRelease(&tree);
  return ok;
}

static int ReadHuffmanCode(int alphabet_size,
                           HuffmanTree* tree,
                           BrotliBitReader* br) {
  int ok = 1;
  int simple_code;
  uint8_t* code_lengths = NULL;

  code_lengths =
      (uint8_t*)BrotliSafeMalloc((uint64_t)alphabet_size,
                                 sizeof(*code_lengths));
  if (code_lengths == NULL) {
    return 0;
  }
  if (!BrotliReadMoreInput(br)) {
    printf("[ReadHuffmanCode] Unexpected end of input.\n");
    return 0;
  }
  simple_code = BrotliReadBits(br, 1);
  BROTLI_LOG_UINT(simple_code);
  if (simple_code) {  // Read symbols, codes & code lengths directly.
    int i;
    int max_bits_counter = alphabet_size - 1;
    int max_bits = 0;
    int symbols[4] = { 0 };
    const int num_symbols = BrotliReadBits(br, 2) + 1;
    while (max_bits_counter) {
      max_bits_counter >>= 1;
      ++max_bits;
    }
    memset(code_lengths, 0, alphabet_size);
    for (i = 0; i < num_symbols; ++i) {
      symbols[i] = BrotliReadBits(br, max_bits);
      code_lengths[symbols[i]] = 2;
    }
    code_lengths[symbols[0]] = 1;
    switch (num_symbols) {
      case 1:
      case 3:
        break;
      case 2:
        code_lengths[symbols[1]] = 1;
        break;
      case 4:
        if (BrotliReadBits(br, 1)) {
          code_lengths[symbols[2]] = 3;
          code_lengths[symbols[3]] = 3;
        } else {
          code_lengths[symbols[0]] = 2;
        }
        break;
    }
    BROTLI_LOG_UINT(num_symbols);
  } else {  // Decode Huffman-coded code lengths.
    int i;
    uint8_t code_length_code_lengths[CODE_LENGTH_CODES] = { 0 };
    const int num_codes = BrotliReadBits(br, 4) + 3;
    BROTLI_LOG_UINT(num_codes);
    if (num_codes > CODE_LENGTH_CODES) {
      return 0;
    }
    for (i = BrotliReadBits(br, 1) * 2; i < num_codes; ++i) {
      int code_len_idx = kCodeLengthCodeOrder[i];
      int v = BrotliReadBits(br, 2);
      if (v == 1) {
        v = BrotliReadBits(br, 1);
        if (v == 0) {
          v = 2;
        } else {
          v = BrotliReadBits(br, 1);
          if (v == 0) {
            v = 1;
          } else {
            v = 5;
          }
        }
      } else if (v == 2) {
        v = 4;
      }
      code_length_code_lengths[code_len_idx] = v;
      BROTLI_LOG_ARRAY_INDEX(code_length_code_lengths, code_len_idx);
    }
    ok = ReadHuffmanCodeLengths(code_length_code_lengths, alphabet_size,
                                code_lengths, br);
  }
  if (ok) {
    ok = BrotliHuffmanTreeBuildImplicit(tree, code_lengths, alphabet_size);
    if (!ok) {
      printf("[ReadHuffmanCode] HuffmanTreeBuildImplicit failed: ");
      PrintUcharVector(code_lengths, alphabet_size);
    }
  }
  free(code_lengths);
  return ok;
}

static int ReadCopyDistance(const HuffmanTree* tree,
                            int num_direct_codes,
                            int postfix_bits,
                            uint32_t postfix_mask,
                            BrotliBitReader* br) {
  int code;
  int nbits;
  int postfix;
  int offset;
  code = ReadSymbol(tree, br);
  if (code < num_direct_codes) {
    return code;
  }
  code -= num_direct_codes;
  postfix = code & postfix_mask;
  code >>= postfix_bits;
  nbits = (code >> 1) + 1;
  offset = ((2 + (code & 1)) << nbits) - 4;
  return (num_direct_codes +
          ((offset + BrotliReadBits(br, nbits)) << postfix_bits) +
          postfix);
}

static int ReadBlockLength(const HuffmanTree* tree, BrotliBitReader* br) {
  int code;
  int nbits;
  code = ReadSymbol(tree, br);
  nbits = kBlockLengthPrefixCode[code].nbits;
  return kBlockLengthPrefixCode[code].offset + BrotliReadBits(br, nbits);
}

static void ReadInsertAndCopy(const HuffmanTree* tree,
                              int* insert_len,
                              int* copy_len,
                              int* copy_dist,
                              BrotliBitReader* br) {
  int code;
  int range_idx;
  int insert_code;
  int insert_extra_bits;
  int copy_code;
  int copy_extra_bits;
  code = ReadSymbol(tree, br);
  range_idx = code >> 6;
  if (range_idx >= 2) {
    range_idx -= 2;
    *copy_dist = -1;
  } else {
    *copy_dist = 0;
  }
  insert_code = kInsertRangeLut[range_idx] + ((code >> 3) & 7);
  copy_code = kCopyRangeLut[range_idx] + (code & 7);
  *insert_len = kInsertLengthPrefixCode[insert_code].offset;
  insert_extra_bits = kInsertLengthPrefixCode[insert_code].nbits;
  if (insert_extra_bits > 0) {
    *insert_len += BrotliReadBits(br, insert_extra_bits);
  }
  *copy_len = kCopyLengthPrefixCode[copy_code].offset;
  copy_extra_bits = kCopyLengthPrefixCode[copy_code].nbits;
  if (copy_extra_bits > 0) {
    *copy_len += BrotliReadBits(br, copy_extra_bits);
  }
}

static int TranslateShortCodes(int code, int* ringbuffer, size_t index) {
  int val;
  if (code < NUM_DISTANCE_SHORT_CODES) {
    index += kDistanceShortCodeIndexOffset[code];
    index &= 3;
    val = ringbuffer[index] + kDistanceShortCodeValueOffset[code];
  } else {
    val = code - NUM_DISTANCE_SHORT_CODES + 1;
  }
  return val;
}

static void MoveToFront(uint8_t* v, uint8_t index) {
  uint8_t value = v[index];
  uint8_t i = index;
  for (; i; --i) v[i] = v[i - 1];
  v[0] = value;
}

static void InverseMoveToFrontTransform(uint8_t* v, int v_len) {
  uint8_t mtf[256];
  int i;
  for (i = 0; i < 256; ++i) {
    mtf[i] = i;
  }
  for (i = 0; i < v_len; ++i) {
    uint8_t index = v[i];
    v[i] = mtf[index];
    if (index) MoveToFront(mtf, index);
  }
}

// Contains a collection of huffman trees with the same alphabet size.
typedef struct {
  int alphabet_size;
  int num_htrees;
  HuffmanTree* htrees;
} HuffmanTreeGroup;

static void HuffmanTreeGroupInit(HuffmanTreeGroup* group, int alphabet_size,
                                 int ntrees) {
  group->alphabet_size = alphabet_size;
  group->num_htrees = ntrees;
  group->htrees = (HuffmanTree*)malloc(sizeof(HuffmanTree) * ntrees);
}

static void HuffmanTreeGroupRelease(HuffmanTreeGroup* group) {
  int i;
  for (i = 0; i < group->num_htrees; ++i) {
    BrotliHuffmanTreeRelease(&group->htrees[i]);
  }
  free(group->htrees);
}

static int HuffmanTreeGroupDecode(HuffmanTreeGroup* group,
                                  BrotliBitReader* br) {
  int i;
  for (i = 0; i < group->num_htrees; ++i) {
    if (!ReadHuffmanCode(group->alphabet_size, &group->htrees[i], br)) {
      return 0;
    }
  }
  return 1;
}

static int DecodeContextMap(int context_map_size,
                            int* num_htrees,
                            uint8_t** context_map,
                            BrotliBitReader* br) {
  int ok = 1;
  if (!BrotliReadMoreInput(br)) {
    printf("[DecodeContextMap] Unexpected end of input.\n");
    return 0;
  }
  *num_htrees = DecodeVarLenUint8(br) + 1;

  BROTLI_LOG_UINT(context_map_size);
  BROTLI_LOG_UINT(*num_htrees);

  *context_map = (uint8_t*)malloc(context_map_size);
  if (*num_htrees <= 1) {
    memset(*context_map, 0, context_map_size);
    return 1;
  }

  {
    HuffmanTree tree_index_htree;
    int use_rle_for_zeros = BrotliReadBits(br, 1);
    int max_run_length_prefix = 0;
    int i;
    if (use_rle_for_zeros) {
      max_run_length_prefix = BrotliReadBits(br, 4) + 1;
    }
    if (!ReadHuffmanCode(*num_htrees + max_run_length_prefix,
                         &tree_index_htree, br)) {
      return 0;
    }
    for (i = 0; i < context_map_size;) {
      int code;
      if (!BrotliReadMoreInput(br)) {
        printf("[DecodeContextMap] Unexpected end of input.\n");
        ok = 0;
        goto End;
      }
      code = ReadSymbol(&tree_index_htree, br);
      if (code == 0) {
        (*context_map)[i] = 0;
        ++i;
      } else if (code <= max_run_length_prefix) {
        int reps = 1 + (1 << code) + BrotliReadBits(br, code);
        while (--reps) {
          (*context_map)[i] = 0;
          ++i;
        }
      } else {
        (*context_map)[i] = code - max_run_length_prefix;
        ++i;
      }
    }
   End:
    BrotliHuffmanTreeRelease(&tree_index_htree);
  }
  if (BrotliReadBits(br, 1)) {
    InverseMoveToFrontTransform(*context_map, context_map_size);
  }
  return ok;
}

static BROTLI_INLINE void DecodeBlockType(const HuffmanTree* trees,
                                         int tree_type,
                                         int* block_types,
                                         int* ringbuffers,
                                         size_t* indexes,
                                         BrotliBitReader* br) {
  int* ringbuffer = ringbuffers + tree_type * 2;
  size_t* index = indexes + tree_type;
  int type_code = ReadSymbol(trees + tree_type, br);
  int block_type;
  if (type_code == 0) {
    block_type = ringbuffer[*index & 1];
  } else if (type_code == 1) {
    block_type = ringbuffer[(*index - 1) & 1] + 1;
  } else {
    block_type = type_code - 2;
  }
  block_types[tree_type] = block_type;
  ringbuffer[(*index) & 1] = block_type;
  ++(*index);
}

// Copy len bytes from src to dst. It can write up to ten extra bytes
// after the end of the copy.
//
// The main part of this loop is a simple copy of eight bytes at a time until
// we've copied (at least) the requested amount of bytes.  However, if dst and
// src are less than eight bytes apart (indicating a repeating pattern of
// length < 8), we first need to expand the pattern in order to get the correct
// results. For instance, if the buffer looks like this, with the eight-byte
// <src> and <dst> patterns marked as intervals:
//
//    abxxxxxxxxxxxx
//    [------]           src
//      [------]         dst
//
// a single eight-byte copy from <src> to <dst> will repeat the pattern once,
// after which we can move <dst> two bytes without moving <src>:
//
//    ababxxxxxxxxxx
//    [------]           src
//        [------]       dst
//
// and repeat the exercise until the two no longer overlap.
//
// This allows us to do very well in the special case of one single byte
// repeated many times, without taking a big hit for more general cases.
//
// The worst case of extra writing past the end of the match occurs when
// dst - src == 1 and len == 1; the last copy will read from byte positions
// [0..7] and write to [4..11], whereas it was only supposed to write to
// position 1. Thus, ten excess bytes.
static BROTLI_INLINE void IncrementalCopyFastPath(
    uint8_t* dst, const uint8_t* src, int len) {
  if (src < dst) {
    while (dst - src < 8) {
      UNALIGNED_COPY64(dst, src);
      len -= dst - src;
      dst += dst - src;
    }
  }
  while (len > 0) {
    UNALIGNED_COPY64(dst, src);
    src += 8;
    dst += 8;
    len -= 8;
  }
}

int BrotliDecompressedSize(size_t encoded_size,
                           const uint8_t* encoded_buffer,
                           size_t* decoded_size) {
  BrotliMemInput memin;
  BrotliInput input = BrotliInitMemInput(encoded_buffer, encoded_size, &memin);
  BrotliBitReader br;
  if (!BrotliInitBitReader(&br, input)) {
    return 0;
  }
  DecodeWindowBits(&br);
  size_t meta_block_len;
  int input_end;
  int is_uncompressed;
  DecodeMetaBlockLength(&br, &meta_block_len, &input_end, &is_uncompressed);
  if (!input_end) {
    return 0;
  }
  *decoded_size = meta_block_len;
  return 1;
}

int BrotliDecompressBuffer(size_t encoded_size,
                           const uint8_t* encoded_buffer,
                           size_t* decoded_size,
                           uint8_t* decoded_buffer) {
  BrotliMemInput memin;
  BrotliInput in = BrotliInitMemInput(encoded_buffer, encoded_size, &memin);
  BrotliMemOutput mout;
  BrotliOutput out = BrotliInitMemOutput(decoded_buffer, *decoded_size, &mout);
  int success = BrotliDecompress(in, out);
  *decoded_size = mout.pos;
  return success;
}

int BrotliDecompress(BrotliInput input, BrotliOutput output) {
  int ok = 1;
  int i;
  size_t pos = 0;
  int input_end = 0;
  int window_bits = 0;
  size_t max_backward_distance;
  size_t ringbuffer_size;
  size_t ringbuffer_mask;
  uint8_t* ringbuffer;
  uint8_t* ringbuffer_end;
  // This ring buffer holds a few past copy distances that will be used by
  // some special distance codes.
  int dist_rb[4] = { 16, 15, 11, 4 };
  size_t dist_rb_idx = 0;
  // The previous 2 bytes used for context.
  uint8_t prev_byte1 = 0;
  uint8_t prev_byte2 = 0;
  HuffmanTreeGroup hgroup[3];
  BrotliBitReader br;

  if (!BrotliInitBitReader(&br, input)) {
    return 0;
  }

  // Decode window size.
  window_bits = DecodeWindowBits(&br);
  max_backward_distance = (1 << window_bits) - 16;

  static const int kRingBufferWriteAheadSlack = 16;

  static const int kMaxDictionaryWordLength = 0;

  ringbuffer_size = 1 << window_bits;
  ringbuffer_mask = ringbuffer_size - 1;
  ringbuffer = (uint8_t*)malloc(ringbuffer_size +
                                kRingBufferWriteAheadSlack +
                                kMaxDictionaryWordLength);
  ringbuffer_end = ringbuffer + ringbuffer_size;

  while (!input_end && ok) {
    size_t meta_block_len = 0;
    size_t meta_block_end_pos;
    int is_uncompressed;
    uint32_t block_length[3] = { 1 << 28, 1 << 28, 1 << 28 };
    int block_type[3] = { 0 };
    int num_block_types[3] = { 1, 1, 1 };
    int block_type_rb[6] = { 0, 1, 0, 1, 0, 1 };
    size_t block_type_rb_index[3] = { 0 };
    HuffmanTree block_type_trees[3];
    HuffmanTree block_len_trees[3];
    int distance_postfix_bits;
    int num_direct_distance_codes;
    uint32_t distance_postfix_mask;
    int num_distance_codes;
    uint8_t* context_map = NULL;
    uint8_t* context_modes = NULL;
    int num_literal_htrees;
    uint8_t* dist_context_map = NULL;
    int num_dist_htrees;
    int context_offset = 0;
    uint8_t* context_map_slice = NULL;
    uint8_t literal_htree_index = 0;
    int dist_context_offset = 0;
    uint8_t* dist_context_map_slice = NULL;
    uint8_t dist_htree_index = 0;
    int context_lookup_offset1 = 0;
    int context_lookup_offset2 = 0;
    uint8_t context_mode;

    for (i = 0; i < 3; ++i) {
      hgroup[i].num_htrees = 0;
      hgroup[i].htrees = NULL;
      block_type_trees[i].root_ = NULL;
      block_len_trees[i].root_ = NULL;
    }

    if (!BrotliReadMoreInput(&br)) {
      printf("[BrotliDecompress] Unexpected end of input.\n");
      ok = 0;
      goto End;
    }
    BROTLI_LOG_UINT(pos);
    DecodeMetaBlockLength(&br, &meta_block_len, &input_end, &is_uncompressed);
    BROTLI_LOG_UINT(meta_block_len);
    if (meta_block_len == 0) {
      goto End;
    }
    meta_block_end_pos = pos + meta_block_len;
    if (is_uncompressed) {
      BrotliSetBitPos(&br, (br.bit_pos_ + 7) & ~7);
      for (; pos < meta_block_end_pos; ++pos) {
        ringbuffer[pos & ringbuffer_mask] = BrotliReadBits(&br, 8);
        if ((pos & ringbuffer_mask) == ringbuffer_mask) {
          if (BrotliWrite(output, ringbuffer, ringbuffer_size) < 0) {
            ok = 0;
            goto End;
          }
        }
      }
      goto End;
    }
    for (i = 0; i < 3; ++i) {
      block_type_trees[i].root_ = NULL;
      block_len_trees[i].root_ = NULL;
      num_block_types[i] = DecodeVarLenUint8(&br) + 1;
      if (num_block_types[i] >= 2) {
        if (!ReadHuffmanCode(
                num_block_types[i] + 2, &block_type_trees[i], &br) ||
            !ReadHuffmanCode(kNumBlockLengthCodes, &block_len_trees[i], &br)) {
          ok = 0;
          goto End;
        }
        block_length[i] = ReadBlockLength(&block_len_trees[i], &br);
        block_type_rb_index[i] = 1;
      }
    }

    BROTLI_LOG_UINT(num_block_types[0]);
    BROTLI_LOG_UINT(num_block_types[1]);
    BROTLI_LOG_UINT(num_block_types[2]);
    BROTLI_LOG_UINT(block_length[0]);
    BROTLI_LOG_UINT(block_length[1]);
    BROTLI_LOG_UINT(block_length[2]);

    if (!BrotliReadMoreInput(&br)) {
      printf("[BrotliDecompress] Unexpected end of input.\n");
      ok = 0;
      goto End;
    }
    distance_postfix_bits = BrotliReadBits(&br, 2);
    num_direct_distance_codes = NUM_DISTANCE_SHORT_CODES +
        (BrotliReadBits(&br, 4) << distance_postfix_bits);
    distance_postfix_mask = (1 << distance_postfix_bits) - 1;
    num_distance_codes = (num_direct_distance_codes +
                          (48 << distance_postfix_bits));
    context_modes = (uint8_t*)malloc(num_block_types[0]);
    for (i = 0; i < num_block_types[0]; ++i) {
      context_modes[i] = BrotliReadBits(&br, 2) << 1;
      BROTLI_LOG_ARRAY_INDEX(context_modes, i);
    }
    BROTLI_LOG_UINT(num_direct_distance_codes);
    BROTLI_LOG_UINT(distance_postfix_bits);

    if (!DecodeContextMap(num_block_types[0] << kLiteralContextBits,
                          &num_literal_htrees, &context_map, &br) ||
        !DecodeContextMap(num_block_types[2] << kDistanceContextBits,
                          &num_dist_htrees, &dist_context_map, &br)) {
      ok = 0;
      goto End;
    }

    HuffmanTreeGroupInit(&hgroup[0], kNumLiteralCodes, num_literal_htrees);
    HuffmanTreeGroupInit(&hgroup[1], kNumInsertAndCopyCodes,
                         num_block_types[1]);
    HuffmanTreeGroupInit(&hgroup[2], num_distance_codes, num_dist_htrees);

    for (i = 0; i < 3; ++i) {
      if (!HuffmanTreeGroupDecode(&hgroup[i], &br)) {
        ok = 0;
        goto End;
      }
    }

    context_map_slice = context_map;
    dist_context_map_slice = dist_context_map;
    context_mode = context_modes[block_type[0]];
    context_lookup_offset1 = kContextLookupOffsets[context_mode];
    context_lookup_offset2 = kContextLookupOffsets[context_mode + 1];

    while (pos < meta_block_end_pos) {
      int insert_length;
      int copy_length;
      int distance_code;
      int distance;
      size_t max_distance;
      uint8_t context;
      int j;
      const uint8_t* copy_src;
      uint8_t* copy_dst;
      if (!BrotliReadMoreInput(&br)) {
        printf("[BrotliDecompress] Unexpected end of input.\n");
        ok = 0;
        goto End;
      }
      if (block_length[1] == 0) {
        DecodeBlockType(block_type_trees, 1, block_type, block_type_rb,
                        block_type_rb_index, &br);
        block_length[1] = ReadBlockLength(&block_len_trees[1], &br);
      }
      --block_length[1];
      ReadInsertAndCopy(&hgroup[1].htrees[block_type[1]],
                        &insert_length, &copy_length, &distance_code, &br);
      BROTLI_LOG_UINT(insert_length);
      BROTLI_LOG_UINT(copy_length);
      BROTLI_LOG_UINT(distance_code);
      for (j = 0; j < insert_length; ++j) {
        if (!BrotliReadMoreInput(&br)) {
          printf("[BrotliDecompress] Unexpected end of input.\n");
          ok = 0;
          goto End;
        }
        if (block_length[0] == 0) {
          DecodeBlockType(block_type_trees, 0, block_type, block_type_rb,
                          block_type_rb_index, &br);
          block_length[0] = ReadBlockLength(&block_len_trees[0], &br);
          context_offset = block_type[0] << kLiteralContextBits;
          context_map_slice = context_map + context_offset;
          context_mode = context_modes[block_type[0]];
          context_lookup_offset1 = kContextLookupOffsets[context_mode];
          context_lookup_offset2 = kContextLookupOffsets[context_mode + 1];
        }
        context = (kContextLookup[context_lookup_offset1 + prev_byte1] |
                   kContextLookup[context_lookup_offset2 + prev_byte2]);
        BROTLI_LOG_UINT(context);
        literal_htree_index = context_map_slice[context];
        --block_length[0];
        prev_byte2 = prev_byte1;
        prev_byte1 = ReadSymbol(&hgroup[0].htrees[literal_htree_index], &br);
        ringbuffer[pos & ringbuffer_mask] = prev_byte1;
        BROTLI_LOG_UINT(literal_htree_index);
        BROTLI_LOG_ARRAY_INDEX(ringbuffer, pos & ringbuffer_mask);
        if ((pos & ringbuffer_mask) == ringbuffer_mask) {
          if (BrotliWrite(output, ringbuffer, ringbuffer_size) < 0) {
            ok = 0;
            goto End;
          }
        }
        ++pos;
      }
      if (pos == meta_block_end_pos) break;

      if (distance_code < 0) {
        if (!BrotliReadMoreInput(&br)) {
          printf("[BrotliDecompress] Unexpected end of input.\n");
          ok = 0;
          goto End;
        }
        if (block_length[2] == 0) {
          DecodeBlockType(block_type_trees, 2, block_type, block_type_rb,
                          block_type_rb_index, &br);
          block_length[2] = ReadBlockLength(&block_len_trees[2], &br);
          dist_htree_index = block_type[2];
          dist_context_offset = block_type[2] << kDistanceContextBits;
          dist_context_map_slice = dist_context_map + dist_context_offset;
        }
        --block_length[2];
        uint8_t context = copy_length > 4 ? 3 : copy_length - 2;
        dist_htree_index = dist_context_map_slice[context];
        distance_code = ReadCopyDistance(&hgroup[2].htrees[dist_htree_index],
                                         num_direct_distance_codes,
                                         distance_postfix_bits,
                                         distance_postfix_mask,
                                         &br);
      }

      // Convert the distance code to the actual distance by possibly looking
      // up past distnaces from the ringbuffer.
      distance = TranslateShortCodes(distance_code, dist_rb, dist_rb_idx);
      if (distance_code > 0) {
        dist_rb[dist_rb_idx & 3] = distance;
        ++dist_rb_idx;
      }
      BROTLI_LOG_UINT(distance);

      max_distance = max_backward_distance;
      if (pos < max_distance) {
        max_distance = pos;
      }

      copy_dst = &ringbuffer[pos & ringbuffer_mask];

      if ((size_t)distance > max_distance) {
        printf("Invalid backward reference. pos: %lu distance: %d "
               "len: %d end: %lu\n", (unsigned long)pos, distance, copy_length,
               (unsigned long)meta_block_end_pos);
        ok = 0;
        goto End;
      } else {
        if (pos + copy_length > meta_block_end_pos) {
          printf("Invalid backward reference. pos: %lu distance: %d "
                 "len: %d end: %lu\n", (unsigned long)pos, distance,
                 copy_length, (unsigned long)meta_block_end_pos);
          ok = 0;
          goto End;
        }

        copy_src = &ringbuffer[(pos - distance) & ringbuffer_mask];

#if (defined(__x86_64__) || defined(_M_X64))
        if (copy_src + copy_length <= ringbuffer_end &&
            copy_dst + copy_length < ringbuffer_end) {
          if (copy_length <= 16 && distance >= 8) {
            UNALIGNED_COPY64(copy_dst, copy_src);
            UNALIGNED_COPY64(copy_dst + 8, copy_src + 8);
          } else {
            IncrementalCopyFastPath(copy_dst, copy_src, copy_length);
          }
          pos += copy_length;
          copy_length = 0;
        }
#endif

        for (j = 0; j < copy_length; ++j) {
          ringbuffer[pos & ringbuffer_mask] =
              ringbuffer[(pos - distance) & ringbuffer_mask];
          if ((pos & ringbuffer_mask) == ringbuffer_mask) {
            if (BrotliWrite(output, ringbuffer, ringbuffer_size) < 0) {
              ok = 0;
              goto End;
            }
          }
          ++pos;
        }
      }

      // When we get here, we must have inserted at least one literal and made
      // a copy of at least length two, therefore accessing the last 2 bytes is
      // valid.
      prev_byte1 = ringbuffer[(pos - 1) & ringbuffer_mask];
      prev_byte2 = ringbuffer[(pos - 2) & ringbuffer_mask];
    }
 End:
    free(context_modes);
    free(context_map);
    free(dist_context_map);
    for (i = 0; i < 3; ++i) {
      HuffmanTreeGroupRelease(&hgroup[i]);
      BrotliHuffmanTreeRelease(&block_type_trees[i]);
      BrotliHuffmanTreeRelease(&block_len_trees[i]);
    }
  }

  if (BrotliWrite(output, ringbuffer, pos & ringbuffer_mask) < 0) {
    ok = 0;
  }
  free(ringbuffer);
  return ok;
}

#if defined(__cplusplus) || defined(c_plusplus)
}    // extern "C"
#endif