huffman_encoder.hpp

#pragma once
 
#include "fly/coders/coder.hpp"
#include "fly/coders/huffman/types.hpp"
 
#include <array>
#include <istream>
#include <memory>
 
namespace fly {
class BitStreamWriter;
} // namespace fly
 
namespace fly::coders {
 
class CoderConfig;
 
class HuffmanEncoder : public BinaryEncoder
{
public:
    explicit HuffmanEncoder(const std::shared_ptr<CoderConfig> &config) noexcept;
 
protected:
    bool encode_binary(std::istream &decoded, fly::BitStreamWriter &encoded) override;
 
private:
    std::uint32_t read_stream(std::istream &decoded) const;
 
    void create_tree(std::uint32_t chunk_size);
 
    void create_codes();
 
    void insert_code(HuffmanCode &&code);
 
    void limit_code_lengths();
 
    void convert_to_canonical_form();
 
    void encode_header(fly::BitStreamWriter &encoded) const;
 
    void encode_codes(fly::BitStreamWriter &encoded) const;
 
    void encode_symbols(std::uint32_t chunk_size, fly::BitStreamWriter &encoded);
 
    // Configuration.
    const std::uint32_t m_chunk_size;
    const length_type m_max_code_length;
 
    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;
 
    // Sized to fit a complete Huffman tree. With 8-bit symbols, a complete tree
    // will have a height of 9, and 2^9 - 1 = 511 nodes (round to 512).
    std::array<HuffmanNode, 1 << 9> m_huffman_tree;
};
 
} // namespace fly::coders