Context-Adaptive Arithmetic Coding with Scaling

A simple implementation of compression method known as context-adaptive arithmetic coding with scaling. What does it mean?

• Arithmetic Coding - coding method used in this program.

• Context-Adaptive - means that the the length of the codes depends on a frequency of individual bytes.

• with Scaling - there is no problem with number precision.

Usage

Type ac --help to get help. General usage:

ac (--encode|--decode) [-o,-s] source [dest]

Available options

  -e,--encode                 Encode a file
  -d,--decode                 Decode a file
  -h,--help                   Print help message and exit
  -o,--override               Whether output file should override existing file.
  -s,--stats                  Print stats during and after encoding process.

By default dest is set to {source}.ac.

Examples

Encoding file with stats printed out (dest file must not exist)

./ac --encode -s file.txt output.ac

Decoding file with progress bar (dest file will be overwritten)

./ac -dso output.ac file2.txt

Project structure

There are currently 3 projects in this workspace.

Project	Description
AC_Core	Core functionality of arithmetic coding. All logic is there including file i/o. This project produces static library that is used in AC_CLI and AC_Core_Tests as a dependency.
AC_CLI	Command-Line Interface for AC_Core functions. This project produces executable program called ac (by default).
AC_Core_Tests	Collection of unit tests for AC_Core functionalities. This project produces executable with embeded CLI from Catch2. For more info read official docs.

External libraries

AC_Core library doesn’t have any external dependencies except C++ standard library.

• CLI11 provides command-line arguments parser for AC_CLI.

• Catch2 is used in AC_Core_Tests as a testing framework.

Building

You need Premake5 to easily generate project files (e.g. for Visual Studio, Code::Blocks, Xcode, GNU Make and more)

In root folder run premake5 with an argument depending on IDE you want to use. For example, run: premake5 vs2019 if you want to generate project for Visual Studio 2019.

Visual Studio (Windows)

In root folder run premak5 vs2019. Visual Studio solution with projects will be generated. Open Arithmetic Coder.sln with Visual Studio. Everything should be configured properly to build, run and test the program.

Makefile (Linux)

In root folder run premake5 [--cc=gcc|clang] gmake2. If --cc option is not set, then default C++ compiler will be used. Makefile files structure will be generated. In root folder run make help to get available build options. General usage is:

make [config=release|debug] [target]

TARGETS:
    all (default)
    AC_CLI
    AC_Core
    AC_Core_Tests

Executable binaries are stored in bin/ folder. Release config is used by default.

Importnat note: Because of using <filesystem> standard library in AC_CLI, AC_Core and AC_Core_Tests projects it is necessary to have it installed on your computer. If you generate project for gcc then library stdc+fs` is automatically linked via `-l` option. Note that `<filesystem>` library is available in gcc since version _8.x_. In earlier versions there was `<experimental/filesystem>`. Since version _9.x_ of gcc it's not necessary to link against `stdc+fs anymore. Clang was not tested.

Tests

Project AC_Core_Tests contains all the tests for AC_Core. You can build it and run executable ac_core_tests to verify tests.

License

Copyright © 2020 KyrietS
Use of this software is granted under the terms of the MIT License.

See the LICENSE for the full license text.