huffman_decoder.hpp

#pragma once
 
#include "fly/coders/coder.hpp"
#include "fly/coders/huffman/types.hpp"
 
#include <array>
#include <memory>
#include <ostream>
 
namespace fly {
class BitStreamReader;
} // namespace fly
 
namespace fly::coders {
 
class HuffmanDecoder : public BinaryDecoder
{
public:
    HuffmanDecoder() noexcept;
 
    code_type compute_kraft_mcmillan_constant() const;
 
protected:
    bool decode_binary(fly::BitStreamReader &encoded, std::ostream &decoded) override;
 
private:
    bool decode_header(fly::BitStreamReader &encoded, std::uint32_t &chunk_size);
 
    bool decode_header_version1(fly::BitStreamReader &encoded, std::uint32_t &chunk_size);
 
    bool decode_codes(fly::BitStreamReader &encoded, length_type &max_code_length);
 
    void convert_to_prefix_table(length_type max_code_length);
 
    bool decode_symbols(
        fly::BitStreamReader &encoded,
        length_type max_code_length,
        std::uint32_t chunk_size,
        std::ostream &decoded) const;
 
    std::unique_ptr<symbol_type[]> m_chunk_buffer;
 
    // Sized to fit 8-bit ASCII symbols.
    std::array<HuffmanCode, 1 << 8> m_huffman_codes;
    std::uint16_t m_huffman_codes_size;
    length_type m_max_code_length;
 
    // Will be sized to fit the global maximum Huffman code length used by the encoder. The size
    // will be 2^L, were L is the maximum code length.
    std::unique_ptr<HuffmanCode[]> m_prefix_table;
};
 
} // namespace fly::coders