You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
87 lines
3.0 KiB
87 lines
3.0 KiB
2 years ago
|
// 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_
|