huffman.hh

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#ifndef __MEM_CACHE_COMPRESSORS_ENCODERS_HUFFMAN_HH__
#define __MEM_CACHE_COMPRESSORS_ENCODERS_HUFFMAN_HH__
 
#include <cassert>
#include <cstdint>
#include <map>
#include <memory>
#include <queue>
#include <vector>
 
#include "base/compiler.hh"
#include "mem/cache/compressors/encoders/base.hh"
 
namespace gem5
{
 
namespace compression
{
namespace encoder
{
 
class Huffman : public Base
{
  public:
    Huffman(uint64_t max_code_length);
    ~Huffman() = default;
 
    void sample(uint64_t value, uint64_t frequency);
 
    void generateCodeMaps();
 
    Code encode(const uint64_t val) const override;
    uint64_t decode(const uint64_t code) const override;
 
  private:
    class Node
    {
      private:
        const uint64_t _frequency;
 
        const uint64_t _value;
 
        std::unique_ptr<Node> _left;
 
        std::unique_ptr<Node> _right;
 
      public:
        Node(uint64_t value, uint64_t frequency)
          : _frequency(frequency), _value(value), _left(), _right()
        {
        }
 
        Node(Node* left, Node* right)
          : _frequency(left->getFrequency() + right->getFrequency()),
            _value(0), _left(left), _right(right)
        {
        }
 
        uint64_t getFrequency() const { return _frequency; }
 
        bool
        isLeaf() const
        {
            return (_left == nullptr) && (_right == nullptr);
        }
 
        uint64_t
        getValue() const
        {
            assert(isLeaf());
            return _value;
        }
 
        const Node* getLeftSubTree() const { return _left.get(); }
        const Node* getRightSubTree() const { return _right.get(); }
    };
 
    const unsigned maxCodeLength;
 
    std::map<uint64_t, Code> valueToCode;
    std::map<uint64_t, uint64_t> codeToValue;
 
    struct NodeComparator
    {
        bool
        operator()(const Node* lhs, const Node* rhs) const
        {
            return lhs->getFrequency() > rhs->getFrequency();
        }
    };
    std::priority_queue<Node*, std::vector<Node*>, NodeComparator> trees;
 
    std::unique_ptr<Node> buildTree();
 
    void generateCodes(const Node* node, const Code& current_code);
};
 
} // namespace encoder
} // namespace compression
} // namespace gem5
 
#endif //__MEM_CACHE_COMPRESSORS_ENCODERS_HUFFMAN_HH__