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///
/// @file
/// @author Julius Pettersson
/// @copyright MIT/Expat License.
/// @brief LZW file archiver
/// @version 3
///
/// This is the C++11 implementation of a Lempel-Ziv-Welch single-file command-line archiver.
/// It uses the simpler fixed-width code compression method.
/// It was written with Doxygen comments.
///
/// http://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Welch
/// http://marknelson.us/2011/11/08/lzw-revisited/
/// http://www.cs.duke.edu/csed/curious/compression/lzw.html
/// http://warp.povusers.org/EfficientLZW/index.html
/// http://en.cppreference.com/
/// http://www.doxygen.org/
///
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <exception>
#include <fstream>
#include <ios>
#include <iostream>
#include <istream>
#include <limits>
#include <map>
#include <memory>
#include <ostream>
#include <stdexcept>
#include <string>
#include <utility>
#include <vector>
namespace {
typedef std::uint16_t CodeType; ///< Type used to store and retrieve codes.
namespace globals {
/// Dictionary Maximum Size (when reached, the dictionary will be reset)
const CodeType dms = std::numeric_limits<CodeType>::max();
} // namespace globals
///
/// @brief Compresses the contents of `is` and writes the result to `os`.
/// @param [in] is input stream
/// @param [out] os output stream
///
void compress(std::istream &is, std::ostream &os)
{
std::map<std::pair<CodeType, char>, CodeType> dictionary;
//std::map<std::vector<char>, CodeType> dictionary;
// "named" lambda function, used to reset the dictionary to its initial contents
const auto reset_dictionary = [&dictionary] {
dictionary.clear();
const int minc = std::numeric_limits<char>::min();
const int maxc = std::numeric_limits<char>::max();
for (int c = minc; c <= maxc; ++c)
dictionary.insert({{globals::dms, static_cast<char> (c)}, dictionary.size()});
};
reset_dictionary();
CodeType i{globals::dms}; // Index
char c;
while (is.get(c))
{
// dictionary's maximum size was reached
if (dictionary.size() == globals::dms)
reset_dictionary();
if (dictionary.count({i, c}) == 0)
{
dictionary.insert({{i, c}, dictionary.size()});
os.write(reinterpret_cast<const char *> (&i), sizeof (CodeType));
i = dictionary.at({globals::dms, c});
}
else
i = dictionary.at({i, c});
}
if (i != globals::dms)
os.write(reinterpret_cast<const char *> (&i), sizeof (CodeType));
}
///
/// @brief Decompresses the contents of `is` and writes the result to `os`.
/// @param [in] is input stream
/// @param [out] os output stream
///
void decompress(std::istream &is, std::ostream &os)
{
std::vector<std::pair<CodeType, char>> dictionary;
// "named" lambda function, used to reset the dictionary to its initial contents
const auto reset_dictionary = [&dictionary] {
dictionary.clear();
dictionary.reserve(globals::dms);
const int minc = std::numeric_limits<char>::min();
const int maxc = std::numeric_limits<char>::max();
for (int c = minc; c <= maxc; ++c)
dictionary.push_back({globals::dms, static_cast<char> (c)});
};
// "named" lambda function, used to rebuild strings
const auto rebuild_string = [&dictionary](CodeType k) -> std::vector<char> {
std::vector<char> s; // String
do
{
s.push_back(dictionary.at(k).second);
k = dictionary.at(k).first;
}
while (k != globals::dms);
std::reverse(s.begin(), s.end());
return s;
};
reset_dictionary();
CodeType i{globals::dms}; // Index
CodeType k; // Key
std::vector<char> s; // String
while (is.read(reinterpret_cast<char *> (&k), sizeof (CodeType)))
{
// dictionary's maximum size was reached
if (dictionary.size() == globals::dms)
reset_dictionary();
if (k > dictionary.size())
throw std::runtime_error("invalid compressed code");
if (k == dictionary.size())
dictionary.push_back({i, rebuild_string(i).front()});
else
if (i != globals::dms)
dictionary.push_back({i, rebuild_string(k).front()});
s = rebuild_string(k);
os.write(&s.front(), s.size());
i = k;
}
if (!is.eof() || is.gcount() != 0)
throw std::runtime_error("corrupted compressed file");
}
///
/// @brief Prints usage information and a custom error message.
/// @param s custom error message to be printed
/// @param su Show Usage information
///
void print_usage(const std::string &s = "", bool su = true)
{
if (!s.empty())
std::cerr << "\nERROR: " << s << '\n';
if (su)
{
std::cerr << "\nUsage:\n";
std::cerr << "\tprogram -flag input_file output_file\n\n";
std::cerr << "Where `flag' is either `c' for compressing, or `d' for decompressing, and\n";
std::cerr << "`input_file' and `output_file' are distinct files.\n\n";
std::cerr << "Examples:\n";
std::cerr << "\tlzw.exe -c license.txt license.lzw\n";
std::cerr << "\tlzw.exe -d license.lzw new_license.txt\n";
}
std::cerr << std::endl;
}
} // namespace
///
/// @brief Actual program entry point.
/// @param argc number of command line arguments
/// @param [in] argv array of command line arguments
/// @retval EXIT_FAILURE for failed operation
/// @retval EXIT_SUCCESS for successful operation
///
int main(int argc, char *argv[])
{
if (argc != 4)
{
print_usage("Wrong number of arguments.");
return EXIT_FAILURE;
}
enum class Mode {
Compress,
Decompress
};
Mode m;
if (std::string(argv[1]) == "-c")
m = Mode::Compress;
else
if (std::string(argv[1]) == "-d")
m = Mode::Decompress;
else
{
print_usage(std::string("flag `") + argv[1] + "' is not recognized.");
return EXIT_FAILURE;
}
const std::size_t buffer_size{1024 * 1024};
// these custom buffers should be larger than the default ones
const std::unique_ptr<char[]> input_buffer(new char[buffer_size]);
const std::unique_ptr<char[]> output_buffer(new char[buffer_size]);
std::ifstream input_file;
std::ofstream output_file;
input_file.rdbuf()->pubsetbuf(input_buffer.get(), buffer_size);
input_file.open(argv[2], std::ios_base::binary);
if (!input_file.is_open())
{
print_usage(std::string("input_file `") + argv[2] + "' could not be opened.");
return EXIT_FAILURE;
}
output_file.rdbuf()->pubsetbuf(output_buffer.get(), buffer_size);
output_file.open(argv[3], std::ios_base::binary);
if (!output_file.is_open())
{
print_usage(std::string("output_file `") + argv[3] + "' could not be opened.");
return EXIT_FAILURE;
}
try
{
input_file.exceptions(std::ios_base::badbit);
output_file.exceptions(std::ios_base::badbit | std::ios_base::failbit);
if (m == Mode::Compress)
compress(input_file, output_file);
else
if (m == Mode::Decompress)
decompress(input_file, output_file);
}
catch (const std::ios_base::failure &f)
{
print_usage(std::string("File input/output failure: ") + f.what() + '.', false);
return EXIT_FAILURE;
}
catch (const std::exception &e)
{
print_usage(std::string("Caught exception: ") + e.what() + '.', false);
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
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