kc3-lang/brotli/enc/prefix.h

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• Hash : 4a7024dc
  Author :
  Date : 2015-10-01T12:08:14
  

  Make the brotli encoder C++98 compatible.
  

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• enc/prefix.h

• // 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.
  //
  // Functions for encoding of integers into prefix codes the amount of extra
  // bits, and the actual values of the extra bits.
  
  #ifndef BROTLI_ENC_PREFIX_H_
  #define BROTLI_ENC_PREFIX_H_
  
  #include "./fast_log.h"
  #include "./types.h"
  
  namespace brotli {
  
  static const int kNumInsertLenPrefixes = 24;
  static const int kNumCopyLenPrefixes = 24;
  static const int kNumCommandPrefixes = 704;
  static const int kNumBlockLenPrefixes = 26;
  static const int kNumDistanceShortCodes = 16;
  static const int kNumDistancePrefixes = 520;
  
  // Represents the range of values belonging to a prefix code:
  // [offset, offset + 2^nbits)
  struct PrefixCodeRange {
    int offset;
    int nbits;
  };
  
  static const PrefixCodeRange kBlockLengthPrefixCode[kNumBlockLenPrefixes] = {
    {   1,  2}, {    5,  2}, {  9,   2}, {  13,  2},
    {  17,  3}, {   25,  3}, {  33,  3}, {  41,  3},
    {  49,  4}, {   65,  4}, {  81,  4}, {  97,  4},
    { 113,  5}, {  145,  5}, { 177,  5}, { 209,  5},
    { 241,  6}, {  305,  6}, { 369,  7}, { 497,  8},
    { 753,  9}, { 1265, 10}, {2289, 11}, {4337, 12},
    {8433, 13}, {16625, 24}
  };
  
  inline void GetBlockLengthPrefixCode(int len,
                                       int* code, int* n_extra, int* extra) {
    *code = 0;
    while (*code < 25 && len >= kBlockLengthPrefixCode[*code + 1].offset) {
      ++(*code);
    }
    *n_extra = kBlockLengthPrefixCode[*code].nbits;
    *extra = len - kBlockLengthPrefixCode[*code].offset;
  }
  
  inline void PrefixEncodeCopyDistance(int distance_code,
                                       int num_direct_codes,
                                       int postfix_bits,
                                       uint16_t* code,
                                       uint32_t* extra_bits) {
    if (distance_code < kNumDistanceShortCodes + num_direct_codes) {
      *code = distance_code;
      *extra_bits = 0;
      return;
    }
    distance_code -= kNumDistanceShortCodes + num_direct_codes;
    distance_code += (1 << (postfix_bits + 2));
    int bucket = Log2Floor(distance_code) - 1;
    int postfix_mask = (1 << postfix_bits) - 1;
    int postfix = distance_code & postfix_mask;
    int prefix = (distance_code >> bucket) & 1;
    int offset = (2 + prefix) << bucket;
    int nbits = bucket - postfix_bits;
    *code = kNumDistanceShortCodes + num_direct_codes +
        ((2 * (nbits - 1) + prefix) << postfix_bits) + postfix;
    *extra_bits = (nbits << 24) | ((distance_code - offset) >> postfix_bits);
  }
  
  }  // namespace brotli
  
  #endif  // BROTLI_ENC_PREFIX_H_
  

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