Stockfish/README.md

Stockfish

A free and strong UCI chess engine.
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Overview

Stockfish is a free and strong UCI chess engine derived from Glaurung 2.1 that analyzes chess positions and computes the optimal moves.

Stockfish does not include a graphical user interface (GUI) that is required to display a chessboard and to make it easy to input moves. These GUIs are developed independently from Stockfish and are available online. Read the documentation for your GUI of choice for information about how to use Stockfish with it.

See also the Stockfish documentation for further usage help.

Files

This distribution of Stockfish consists of the following files:

• README.md, the file you are currently reading.

• Copying.txt, a text file containing the GNU General Public License version 3.

• AUTHORS, a text file with the list of authors for the project.

• src, a subdirectory containing the full source code, including a Makefile that can be used to compile Stockfish on Unix-like systems.

• a file with the .nnue extension, storing the neural network for the NNUE evaluation. Binary distributions will have this file embedded.

Stockfish on distributed memory systems

The cluster branch allows for running Stockfish on a cluster of servers (nodes) that are connected with a high-speed and low-latency network, using the message passing interface (MPI). In this case, one MPI process should be run per node, and UCI options can be used to set the number of threads/hash per node as usual. Typically, the engine will be invoked as

mpirun -np N /path/to/stockfish

where N stands for the number of MPI processes used (alternatives to mpirun, include mpiexec, srun). Use 1 mpi rank per node, and employ threading according to the cores per node. To build the cluster branch, it is sufficient to specify COMPCXX=mpicxx (or e.g. CC depending on the name of the compiler providing MPI support) on the make command line, and do a clean build:

make -j ARCH=x86-64-modern clean build COMPCXX=mpicxx mpi=yes

Make sure that the MPI installation is configured to support MPI_THREAD_MULTIPLE, this might require adding system specific compiler options to the Makefile. Stockfish employs non-blocking (asynchronous) communication, and benefits from an MPI implementation that efficiently supports this. Some MPI implentations might benefit from leaving 1 core/thread free for these asynchronous communications, and might require setting additional environment variables. mpirun should forward stdin/stdout to rank 0 only (e.g. srun --input=0 --output=0). Refer to your MPI documentation for more info.

Contributing

See Contributing Guide.

Donating hardware

Improving Stockfish requires a massive amount of testing. You can donate your hardware resources by installing the Fishtest Worker and viewing the current tests on Fishtest.

Improving the code

In the chessprogramming wiki, many techniques used in Stockfish are explained with a lot of background information. The section on Stockfish describes many features and techniques used by Stockfish. However, it is generic rather than focused on Stockfish's precise implementation.

The engine testing is done on Fishtest. If you want to help improve Stockfish, please read this guideline first, where the basics of Stockfish development are explained.

Discussions about Stockfish take place these days mainly in the Stockfish Discord server. This is also the best place to ask questions about the codebase and how to improve it.

Compiling Stockfish

Stockfish has support for 32 or 64-bit CPUs, certain hardware instructions, big-endian machines such as Power PC, and other platforms.

On Unix-like systems, it should be easy to compile Stockfish directly from the source code with the included Makefile in the folder src. In general, it is recommended to run make help to see a list of make targets with corresponding descriptions. An example suitable for most Intel and AMD chips:

cd src
make -j profile-build ARCH=x86-64-avx2

Detailed compilation instructions for all platforms can be found in our documentation. Our wiki also has information about the UCI commands supported by Stockfish.

Terms of use

Stockfish is free and distributed under the GNU General Public License version 3 (GPL v3). Essentially, this means you are free to do almost exactly what you want with the program, including distributing it among your friends, making it available for download from your website, selling it (either by itself or as part of some bigger software package), or using it as the starting point for a software project of your own.

The only real limitation is that whenever you distribute Stockfish in some way, you MUST always include the license and the full source code (or a pointer to where the source code can be found) to generate the exact binary you are distributing. If you make any changes to the source code, these changes must also be made available under GPL v3.