brotli/dec/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.
//
// Lookup tables to map prefix codes to value ranges. This is used during
// decoding of the block lengths, literal insertion lengths and copy lengths.

#ifndef BROTLI_DEC_PREFIX_H_
#define BROTLI_DEC_PREFIX_H_

// Represents the range of values belonging to a prefix code:
// [offset, offset + 2^nbits)
struct PrefixCodeRange {
  int offset;
  int nbits;
};

static const struct PrefixCodeRange kBlockLengthPrefixCode[] = {
  {   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}
};

static const struct PrefixCodeRange kInsertLengthPrefixCode[] = {
  {   0,  0}, {   1,  0}, {  2,   0}, {    3,  0},
  {   4,  0}, {   5,  0}, {  6,   1}, {    8,  1},
  {  10,  2}, {  14,  2}, { 18,   3}, {   26,  3},
  {  34,  4}, {  50,  4}, { 66,   5}, {   98,  5},
  { 130,  6}, { 194,  7}, { 322,  8}, {  578,  9},
  {1090, 10}, {2114, 12}, {6210, 14}, {22594, 24},
};

static const struct PrefixCodeRange kCopyLengthPrefixCode[] = {
  {  2, 0}, {   3,  0}, {   4,  0}, {   5,  0},
  {  6, 0}, {   7,  0}, {   8,  0}, {   9,  0},
  { 10, 1}, {  12,  1}, {  14,  2}, {  18,  2},
  { 22, 3}, {  30,  3}, {  38,  4}, {  54,  4},
  { 70, 5}, { 102,  5}, { 134,  6}, { 198,  7},
  {326, 8}, { 582,  9}, {1094, 10}, {2118, 24},
};

static const int kInsertRangeLut[9] = {
  0, 0, 8, 8, 0, 16, 8, 16, 16,
};

static const int kCopyRangeLut[9] = {
  0, 8, 0, 8, 16, 0, 16, 8, 16,
};

#endif  // BROTLI_DEC_PREFIX_H_