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/* Copyright 2010 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at
// Entropy encoding (Huffman) utilities.
#include <string.h>
#include <vector>
#include "./histogram.h"
#include "./prefix.h"
#include "./types.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
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