Joost VandeVondele
2cbc20e846
Currently (after #5407), SF has the property that any PV line with a decisive TB score contains the corresponding TB position, with a score that correctly identifies the depth at which TB are entered. The PV line that follows might not preserve the game outcome, but can easily be verified and extended based on TB information. This patch provides this functionality, simply extending the PV lines on output, this doesn't affect search. Indeed, if DTZ tables are available, search based PV lines that correspond to decisive TB scores are verified to preserve game outcome, truncating the line as needed. Subsequently, such PV lines are extended with a game outcome preserving line until mate, as a possible continuation. These lines are not optimal mating lines, but are similar to what a user could produce on a website like https://syzygy-tables.info/ clicking always the top ranked move, i.e. minimizing or maximizing DTZ (with a simple tie-breaker for moves that have identical DTZ), and are thus an just an illustration of how to game can be won. A similar approach is already in established in https://github.com/joergoster/Stockfish/tree/matefish2 This also contributes to addressing #5175 where SF can give an incorrect TB win/loss for positions in TB with a movecounter that doesn't reflect optimal play. While the full solution requires either TB generated differently, or a search when ranking rootmoves, current SF will eventually find a draw in these cases, in practice quite quickly, e.g. `1kq5/q2r4/5K2/8/8/8/8/7Q w - - 96 1` `8/8/6k1/3B4/3K4/4N3/8/8 w - - 54 106` Gives the same results as master on an extended set of test positions from https://github.com/mcostalba/Stockfish/commit/9173d29c414ddb8f4bec74e4db3ccbe664c66bf9 with the exception of the above mentioned fen where this commit improves. With https://github.com/vondele/matetrack using 6men TB, all generated PVs verify: ``` Using ../Stockfish/src/stockfish.syzygyExtend on matetrack.epd with --nodes 1000000 --syzygyPath /chess/syzygy/3-4-5-6/WDL:/chess/syzygy/3-4-5-6/DTZ Engine ID: Stockfish dev-20240704-ff227954 Total FENs: 6555 Found mates: 3299 Best mates: 2582 Found TB wins: 568 ``` As repeated DTZ probing could be slow a procedure (100ms+ on HDD, a few ms on SSD), the extension is only done as long as the time taken is less than half the `Move Overhead` parameter. For tournaments where these lines might be of interest to the user, a suitable `Move Overhead` might be needed (e.g. TCEC has 1000ms already). closes https://github.com/official-stockfish/Stockfish/pull/5414 No functional change
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:
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README.md, the file you are currently reading.
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Copying.txt, a text file containing the GNU General Public License version 3.
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AUTHORS, a text file with the list of authors for the project.
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src, a subdirectory containing the full source code, including a Makefile that can be used to compile Stockfish on Unix-like systems.
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a file with the .nnue extension, storing the neural network for the NNUE evaluation. Binary distributions will have this file embedded.
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.