89 lines
2.4 KiB
C++
89 lines
2.4 KiB
C++
/**
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* \file compress.cc
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* \brief Implementation of compression
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*/
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#include "compress.hh"
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#include "common.hh"
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#include "io.hh"
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#include <cassert>
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#include <cstdlib>
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#include <fstream>
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#include <iterator>
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using std::ios;
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using std::string;
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using std::uint16_t;
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using std::uint8_t;
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using std::vector;
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using vuint16 = vector<uint16_t>;
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using vvuint16 = vector<vuint16>;
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using ustring = std::basic_string<unsigned char>;
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using dict_t = std::map<std::pair<uint16_t, uint8_t>, uint16_t>;
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using std::printf;
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ustring read_file(const string &filename) {
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std::ifstream file{filename, ios::binary};
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assert(file);
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file.unsetf(ios::skipws);
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file.seekg(0, ios::end);
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const auto file_size = file.tellg();
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file.seekg(0, ios::beg);
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ustring res{};
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res.reserve(file_size);
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res.insert(res.begin(), std::istream_iterator<unsigned char>(file),
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std::istream_iterator<unsigned char>());
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file.close();
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return res;
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}
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vvuint16 lzw_compress(ustring &&t_text) {
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vvuint16 res{};
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const auto DICT_MAX = static_cast<size_t>(ipow(2, 14) - 256); /* 16 bits */
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uint16_t w = 0xFFFF;
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vuint16 chunk{};
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dict_t dict{};
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for (const auto c : t_text) {
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if (dict.size() >= DICT_MAX) {
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res.push_back(chunk);
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w = 0xFFFF;
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chunk.clear();
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dict.clear();
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}
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if (const auto &[exists, pos] = dico(dict, w, static_cast<uint8_t>(c));
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exists) {
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w = pos;
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} else {
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chunk.push_back(w);
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w = static_cast<uint16_t>(c);
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}
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}
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if (w != 0xFFFF) {
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chunk.push_back(w);
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res.push_back(std::move(chunk));
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}
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return res;
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}
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/**
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* Wrapper de la fonction \ref lzw_compress gérant l'ouverture, la lecture,
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* l'écriture et la fermeture des fichiers d’entrée et de sortie. Si \p
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* t_out_file est nul (chemin non spécifié), il prendra alors la valeur de
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* \p t_in_file à laquelle sera annexé l’extension `.lzw`.
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*
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* \param[in] t_in_file Chemin vers le fichier d’entrée
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* \param[in] t_out_file Chemin vers le fichier de sortie
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*/
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void compress(const std::string &t_in_file, const char *t_out_file) {
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std::ofstream out{(t_out_file != nullptr) ? t_out_file : "output.lzw",
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ios::out | ios::binary};
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if (!out.is_open()) {
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std::cerr << "Error at " << __FILE__ << ":" << __LINE__ - 4
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<< ": could not open output file. Aborting...\n";
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exit(1);
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}
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const auto compressed_text(lzw_compress(read_file(t_in_file)));
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write_file(out, compressed_text);
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out.close();
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}
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