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// 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 <stdint.h>
#include "./fast_log.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) {
distance_code -= 1;
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_