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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.
//
// Models the histograms of literals, commands and distance codes.
#ifndef BROTLI_ENC_HISTOGRAM_H_
#define BROTLI_ENC_HISTOGRAM_H_
#include <stdint.h>
#include <string.h>
#include <vector>
#include <utility>
#include "./command.h"
#include "./fast_log.h"
#include "./prefix.h"
namespace brotli {
class BlockSplit;
// A simple container for histograms of data in blocks.
template<int kDataSize>
struct Histogram {
Histogram() {
Clear();
}
void Clear() {
memset(data_, 0, sizeof(data_));
total_count_ = 0;
}
void Add(int val) {
++data_[val];
++total_count_;
}
void Remove(int val) {
--data_[val];
--total_count_;
}
template<typename DataType>
void Add(const DataType *p, size_t n) {
total_count_ += n;
n += 1;
while(--n) ++data_[*p++];
}
void AddHistogram(const Histogram& v) {
total_count_ += v.total_count_;
for (int i = 0; i < kDataSize; ++i) {
data_[i] += v.data_[i];
}
}
double EntropyBitCost() const {
double retval = total_count_ * FastLog2(total_count_);
for (int i = 0; i < kDataSize; ++i) {
retval -= data_[i] * FastLog2(data_[i]);
}
return retval;
}
int data_[kDataSize];
int total_count_;
double bit_cost_;
};
// Literal histogram.
typedef Histogram<256> HistogramLiteral;
// Prefix histograms.
typedef Histogram<kNumCommandPrefixes> HistogramCommand;
typedef Histogram<kNumDistancePrefixes> HistogramDistance;
typedef Histogram<kNumBlockLenPrefixes> HistogramBlockLength;
// Context map histogram, 256 Huffman tree indexes + 16 run length codes.
typedef Histogram<272> HistogramContextMap;
// Block type histogram, 256 block types + 2 special symbols.
typedef Histogram<258> HistogramBlockType;
static const int kLiteralContextBits = 6;
static const int kDistanceContextBits = 2;
void BuildHistograms(
const std::vector<Command>& cmds,
const BlockSplit& literal_split,
const BlockSplit& insert_and_copy_split,
const BlockSplit& dist_split,
const uint8_t* ringbuffer,
size_t pos,
size_t mask,
const std::vector<int>& context_modes,
std::vector<HistogramLiteral>* literal_histograms,
std::vector<HistogramCommand>* insert_and_copy_histograms,
std::vector<HistogramDistance>* copy_dist_histograms);
void BuildLiteralHistogramsForBlockType(
const std::vector<Command>& cmds,
const BlockSplit& literal_split,
const uint8_t* ringbuffer,
size_t pos,
size_t mask,
int block_type,
int context_mode,
std::vector<HistogramLiteral>* histograms);
} // namespace brotli
#endif // BROTLI_ENC_HISTOGRAM_H_