d889bb4718
This is a functional change that rewards double attacks on an unsupported pawns. STC (non-functional difference) LLR: 2.96 (-2.94,2.94) [0.50,4.50] Total: 83276 W: 18981 L: 18398 D: 45897 http://tests.stockfishchess.org/tests/view/5d0970500ebc5925cf0a77d4 LTC (incomplete looping version) LLR: 0.50 (-2.94,2.94) [0.00,3.50] Total: 82999 W: 14244 L: 13978 D: 54777 http://tests.stockfishchess.org/tests/view/5d0a8d480ebc5925cf0a8d58 LTC (completed non-looping version). LLR: 2.96 (-2.94,2.94) [0.00,3.50] Total: 223381 W: 38323 L: 37512 D: 147546 http://tests.stockfishchess.org/tests/view/5d0e80510ebc5925cf0ad320 Closes https://github.com/official-stockfish/Stockfish/pull/2205 Bench 3633546 ---------------------------------- Comments by Alain SAVARD: interesting result ! I would have expected that search would resolve such positions correctly on the very next move. This is not a very common pattern, and when it happens, it will quickly disappear. So I'm quite surprised that it passed LTC. I would be even more surprised if this would resist a simplification. Anyway, let's try to imagine a few cases. a) If you have White d5 f5 against Black e6, and White to move last move by Black was probably a capture on e6 and White is about to recapture on e6 b) If you have White d5 f5 against e6, and Black to move last move by White was possibly a capture on d5 or f5 or the pawn on e6 was pinned or could not move for some reason. and white wants to blast open the position and just pushed d4-d5 or f4-f5 Some possible follow-ups a) Motif is so rare that the popcount() can be safely replaced with a bool() But this would not pass a SPRT[0,4], So try a simplification with bool() and also without the & ~theirAttacks b) If it works, we probably can simply have this in the loop if (lever) score += S(0, 20); c) remove all this and tweak something in search for pawn captures (priority, SEE, extension,..) |
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| tests | ||
| .travis.yml | ||
| appveyor.yml | ||
| AUTHORS | ||
| Copying.txt | ||
| Readme.md | ||
| Top CPU Contributors.txt | ||
Overview
Stockfish is a free, powerful UCI chess engine derived from Glaurung 2.1. It is not a complete chess program and requires a UCI-compatible GUI (e.g. XBoard with PolyGlot, Scid, Cute Chess, eboard, Arena, Sigma Chess, Shredder, Chess Partner or Fritz) in order to be used comfortably. Read the documentation for your GUI of choice for information about how to use Stockfish with it.
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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src, a subdirectory containing the full source code, including a Makefile that can be used to compile Stockfish on Unix-like systems.
UCI parameters
Currently, Stockfish has the following UCI options:
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Debug Log File
Write all communication to and from the engine into a text file.
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Contempt
A positive value for contempt favors middle game positions and avoids draws.
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Analysis Contempt
By default, contempt is set to prefer the side to move. Set this option to "White" or "Black" to analyse with contempt for that side, or "Off" to disable contempt.
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Threads
The number of CPU threads used for searching a position. For best performance, set this equal to the number of CPU cores available.
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Hash
The size of the hash table in MB.
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Clear Hash
Clear the hash table.
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Ponder
Let Stockfish ponder its next move while the opponent is thinking.
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MultiPV
Output the N best lines (principal variations, PVs) when searching. Leave at 1 for best performance.
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Skill Level
Lower the Skill Level in order to make Stockfish play weaker.
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Move Overhead
Assume a time delay of x ms due to network and GUI overheads. This is useful to avoid losses on time in those cases.
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Minimum Thinking Time
Search for at least x ms per move.
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Slow Mover
Lower values will make Stockfish take less time in games, higher values will make it think longer.
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nodestime
Tells the engine to use nodes searched instead of wall time to account for elapsed time. Useful for engine testing.
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UCI_Chess960
An option handled by your GUI. If true, Stockfish will play Chess960.
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UCI_AnalyseMode
An option handled by your GUI.
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SyzygyPath
Path to the folders/directories storing the Syzygy tablebase files. Multiple directories are to be separated by ";" on Windows and by ":" on Unix-based operating systems. Do not use spaces around the ";" or ":".
Example:
C:\tablebases\wdl345;C:\tablebases\wdl6;D:\tablebases\dtz345;D:\tablebases\dtz6It is recommended to store .rtbw files on an SSD. There is no loss in storing the .rtbz files on a regular HD. It is recommended to verify all md5 checksums of the downloaded tablebase files (
md5sum -c checksum.md5) as corruption will lead to engine crashes. -
SyzygyProbeDepth
Minimum remaining search depth for which a position is probed. Set this option to a higher value to probe less agressively if you experience too much slowdown (in terms of nps) due to TB probing.
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Syzygy50MoveRule
Disable to let fifty-move rule draws detected by Syzygy tablebase probes count as wins or losses. This is useful for ICCF correspondence games.
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SyzygyProbeLimit
Limit Syzygy tablebase probing to positions with at most this many pieces left (including kings and pawns).
What to expect from Syzygybases?
If the engine is searching a position that is not in the tablebases (e.g. a position with 8 pieces), it will access the tablebases during the search. If the engine reports a very large score (typically 153.xx), this means that it has found a winning line into a tablebase position.
If the engine is given a position to search that is in the tablebases, it will use the tablebases at the beginning of the search to preselect all good moves, i.e. all moves that preserve the win or preserve the draw while taking into account the 50-move rule. It will then perform a search only on those moves. The engine will not move immediately, unless there is only a single good move. The engine likely will not report a mate score even if the position is known to be won.
It is therefore clear that this behaviour is not identical to what one might be used to with Nalimov tablebases. There are technical reasons for this difference, the main technical reason being that Nalimov tablebases use the DTM metric (distance-to-mate), while Syzygybases use a variation of the DTZ metric (distance-to-zero, zero meaning any move that resets the 50-move counter). This special metric is one of the reasons that Syzygybases are more compact than Nalimov tablebases, while still storing all information needed for optimal play and in addition being able to take into account the 50-move rule.
Compiling Stockfish yourself from the sources
On Unix-like systems, it should be possible to compile Stockfish directly from the source code with the included Makefile.
Stockfish has support for 32 or 64-bit CPUs, the hardware POPCNT instruction, big-endian machines such as Power PC, and other platforms.
In general it is recommended to run make help to see a list of make
targets with corresponding descriptions. When not using the Makefile to
compile (for instance with Microsoft MSVC) you need to manually
set/unset some switches in the compiler command line; see file types.h
for a quick reference.
Understanding the code base and participating in the project
Stockfish's improvement over the last couple of years has been a great community effort. There are a few ways to help contribute to its growth.
Donating hardware
Improving Stockfish requires a massive amount of testing. You can donate your hardware resources by installing the Fishtest Worker and view the current tests on Fishtest.
Improving the code
If you want to help improve the code, there are several valuable ressources:
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In this wiki, many techniques used in Stockfish are explained with a lot of background information.
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The section on Stockfish describes many features and techniques used by Stockfish. However, it is generic rather than being focused on Stockfish's precise implementation. Nevertheless, a helpful resource.
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The latest source can always be found on GitHub. Discussions about Stockfish take place in the FishCooking group and 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.
Terms of use
Stockfish is free, and distributed under the GNU General Public License version 3 (GPL v3). Essentially, this means that 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 web site, 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 full source code, or a pointer to where the source code can be found. If you make any changes to the source code, these changes must also be made available under the GPL.
For full details, read the copy of the GPL v3 found in the file named Copying.txt.