mirror of
https://github.com/google/brotli.git
synced 2024-12-01 15:30:07 +00:00
89 lines
3.0 KiB
C++
89 lines
3.0 KiB
C++
// Copyright 2010 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.
|
|
//
|
|
// Entropy encoding (Huffman) utilities.
|
|
|
|
#ifndef BROTLI_ENC_ENTROPY_ENCODE_H_
|
|
#define BROTLI_ENC_ENTROPY_ENCODE_H_
|
|
|
|
#include <stdint.h>
|
|
#include <string.h>
|
|
#include <vector>
|
|
#include "./histogram.h"
|
|
#include "./prefix.h"
|
|
|
|
namespace brotli {
|
|
|
|
// This function will create a Huffman tree.
|
|
//
|
|
// The (data,length) contains the population counts.
|
|
// The tree_limit is the maximum bit depth of the Huffman codes.
|
|
//
|
|
// The depth contains the tree, i.e., how many bits are used for
|
|
// the symbol.
|
|
//
|
|
// See http://en.wikipedia.org/wiki/Huffman_coding
|
|
void CreateHuffmanTree(const int *data,
|
|
const int length,
|
|
const int tree_limit,
|
|
uint8_t *depth);
|
|
|
|
// Change the population counts in a way that the consequent
|
|
// Huffman tree compression, especially its rle-part will be more
|
|
// likely to compress this data more efficiently.
|
|
//
|
|
// length contains the size of the histogram.
|
|
// counts contains the population counts.
|
|
int OptimizeHuffmanCountsForRle(int length, int* counts);
|
|
|
|
// Write a Huffman tree from bit depths into the bitstream representation
|
|
// of a Huffman tree. The generated Huffman tree is to be compressed once
|
|
// more using a Huffman tree
|
|
void WriteHuffmanTree(const uint8_t* depth,
|
|
uint32_t num,
|
|
std::vector<uint8_t> *tree,
|
|
std::vector<uint8_t> *extra_bits_data);
|
|
|
|
// Get the actual bit values for a tree of bit depths.
|
|
void ConvertBitDepthsToSymbols(const uint8_t *depth, int len, uint16_t *bits);
|
|
|
|
template<int kSize>
|
|
struct EntropyCode {
|
|
// How many bits for symbol.
|
|
uint8_t depth_[kSize];
|
|
// Actual bits used to represent the symbol.
|
|
uint16_t bits_[kSize];
|
|
// How many non-zero depth.
|
|
int count_;
|
|
// First four symbols with non-zero depth.
|
|
int symbols_[4];
|
|
};
|
|
|
|
static const int kCodeLengthCodes = 18;
|
|
|
|
// Literal entropy code.
|
|
typedef EntropyCode<256> EntropyCodeLiteral;
|
|
// Prefix entropy codes.
|
|
typedef EntropyCode<kNumCommandPrefixes> EntropyCodeCommand;
|
|
typedef EntropyCode<kNumDistancePrefixes> EntropyCodeDistance;
|
|
typedef EntropyCode<kNumBlockLenPrefixes> EntropyCodeBlockLength;
|
|
// Context map entropy code, 256 Huffman tree indexes + 16 run length codes.
|
|
typedef EntropyCode<272> EntropyCodeContextMap;
|
|
// Block type entropy code, 256 block types + 2 special symbols.
|
|
typedef EntropyCode<258> EntropyCodeBlockType;
|
|
|
|
} // namespace brotli
|
|
|
|
#endif // BROTLI_ENC_ENTROPY_ENCODE_H_
|