SoFCheck 🦉♟

                 /    ^---^    \
                /    / @ @ \    \
               ||    \  v  /    ||
               ||    /     \    ||
               ||   / /   \ \   ||
               ||   \/\___/\/   ||
                \      | |      /
                 \     ^ ^     /
   __          ___      __
  /  \        |        /  \  |                |
  \__    __   |__     /      |__    __    __  |
     \  /  \  |       \      |  |  /__\  /    |_/
  \__/  \__/  |        \__/  |  |  \__   \__  | \

SoFCheck plays on CCRL and Lichess.

About

SoFCheck is a chess engine. As many other chess engines, it uses magic bitboards to generate moves and alpha-beta pruning to find out how to analyze positions. The main features of SoFCheck are:

• Speed: the critical parts of the program are written to be as fast as possible
• Multithreading: SoFCheck uses lazy SMP to perform search in multiple threads simultaneously
• Reusability: the parts of SoFCheck can be used as a general-purpose chess library. Also, you can relatively easy add new communication protocols to the engine or integrate it into your GUI. Now the engine supports only UCI, but the situation may change in the future
• Measurability: all the changes in the engine are verified to ensure that new version doesn't play weaker than the previous one. To achieve this, it's a good idea to run matches between different versions of the engine

To learn more, see the project design and how it works.

State of the project

The project is in beta stage. It means that the engine plays strong enough (~2400-2500 Elo, according to my rough estimation), but there is still much space for improvement.

Building from source

The project is using CMake as a build system. You will also need a C++17-compatible compiler. The engine should build fine with the following compilers:

• GCC >= 8 (GCC 12 is used in CI). GCC <= 7 won't work.
• Clang >= 8 (Clang 14 is used in CI). Clang <= 7 won't work.
• Visual Studio >= 2019 (VS 2019 is used in CI). Visual Studio <= 2017 won't work.

Note that MSVC is not supported as good as GCC and Clang, and the resulting binaries may be slower. Be aware of it.

Other compilers are not tested.

The following dependencies are optional:

• Google Test: to run the unit tests
• Google Benchmark: to run benchmarks
• boost::stacktrace: to display stack traces when the application panics
• jsoncpp: to extract evaluation weights located in a JSON file. This one isn't compiled into the final executable and is used only for building and tuning the engine. If you don't install jsoncpp, the version located in third-party/jsoncpp will be used
• cxxopts: to parse command line parameters in source code generators and other development utilities. If you don't install cxxopts, the version located in third-party/cxxopts will be used

To install them all on Debian/Ubuntu, use

$ sudo apt install libgtest-dev libbenchmark-dev libboost-stacktrace-dev libjsoncpp-dev

You may also install libcxxopts-dev (version 3.0.0 or later is required), but it's present in quite new distro releases (Ubuntu 22.04+ and Debian 12+)

To build the engine, do the following:

$ mkdir build
$ cd build
$ cmake ..
$ make -j8

You may also want to build the engine in release mode with maximum optimization. To do this, use

$ mkdir build
$ cd build
$ cmake -DCMAKE_BUILD_TYPE=Release -DCPU_ARCH_LEVEL=BMI2 -DUSE_NO_EXCEPTIONS=ON -DUSE_LTO=ON ..
$ make -j8

For more flags, refer to corresponding CMake scripts (like CMakeLists.txt or cmake/Platform.cmake) or use CMake GUI.

Note on -DCPU_ARCH_LEVEL=BMI2: it should be used only on modern Intel CPUs and on AMD with Zen 3 (or later) microarchitecture. Older AMD CPUs have a very slow implementation of PDEP and PEXT instructions, so using this flag may slow down the engine greatly.

Running tests

SoFCheck uses CTest. So, you can just invoke ctest in build/ directory after you built the engine.

Thanks to

• Chess Programming Wiki, for many useful articles and descriptions of various useful heuristics.
• Andrey Brenkman, author of Ifrit chess engine, for well-commented source code of Ifrit. While looking at these sources, some ideas on how to use the heuristics in search became clearer to me.
• CCRL testers for testing the engine, and especially Graham Banks for awesome tournaments ;)

License

License: GPL 3+.

SoFCheck is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

SoFCheck is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.