d71adc5bd9
This patch simplifies the time management code, removing the extra thinking time for moves with draw PV and increasing thinking time for all moves proportionally by around 4%. Last time when the time management was carefully tuned was 1.5-2 years ago. As new patches were getting added, time management was drifting out of optimum. This happens because when search becomes more precise pv and score are becoming more stable, there are less fail lows, best move is picked earlier and there are less best move changes. All this factors are entering in time management, and average time per move is decreasing with more and more good patches. For individual patches such effect is small (except some) and may be up or down, but when there are many of them, effect is more substantial. The same way benchmark with more and more patches is slowly drifting down on average. So my understanding that back in October adding more think time for draw PV showed positive Elo because time management was not well tuned, there was more time available, and think_hard patch applied this additional time to moves with draw PV, while just retuning back to optimum would recover Elo anyway. It is possible that absence of contempt also helped, as SF9 is showing less 0.0 scores than the October version. Anyway, to me it seems that proper place to deal with draw PV is search, and contempt sounds as much better solution. In time management there is little additional elo, and if some code is not helping like removed here, it is better to discard it. It is simpler to find genuine improvement if code is clean. • Passed STC: LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 20487 W: 4558 L: 4434 D: 11495 http://tests.stockfishchess.org/tests/view/5a7706ec0ebc5902971a9854 • Passed LTC: LLR: 2.96 (-2.94,2.94) [-3.00,1.00] Total: 41960 W: 7145 L: 7058 D: 27757 http://tests.stockfishchess.org/tests/view/5a778c830ebc5902971a9895 • Passed an additional non-regression [-5..0] test at the time control of 60sec for the game (sudden death) with disabled draw adjudication: LLR: 2.95 (-2.94,2.94) [-5.00,0.00] Total: 8438 W: 1675 L: 1586 D: 5177 http://tests.stockfishchess.org/tests/view/5a7c3d8d0ebc5902971a9ac0 • Passed an additional non-regression [-5..0] test at the time control of 1sec+1sec per move with disabled draw adjudication: LLR: 2.97 (-2.94,2.94) [-5.00,0.00] Total: 27664 W: 5575 L: 5574 D: 16515 http://tests.stockfishchess.org/tests/view/5a7c3e820ebc5902971a9ac3 This is a functional change for the time management code. Bench: 4983414 |
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| src | ||
| tests | ||
| .travis.yml | ||
| appveyor.yml | ||
| AUTHORS | ||
| Copying.txt | ||
| Readme.md | ||
| Top CPU Contributors.txt | ||
Overview
Stockfish is a free UCI chess engine derived from Glaurung 2.1. It is not a complete chess program and requires some UCI-compatible GUI (e.g. XBoard with PolyGlot, 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.
This version of Stockfish supports up to 512 cores. The engine defaults to one search thread, so it is therefore recommended to inspect the value of the Threads UCI parameter, and to make sure it equals the number of CPU cores on your computer.
This version of Stockfish has support for Syzygybases.
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.
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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.
Syzygybases
Configuration
Syzygybases are configured using the UCI options "SyzygyPath", "SyzygyProbeDepth", "Syzygy50MoveRule" and "SyzygyProbeLimit".
The option "SyzygyPath" should be set to the directory or directories that contain the .rtbw and .rtbz files. Multiple directories should 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\dtz6
It is recommended to store .rtbw files on an SSD. There is no loss in storing the .rtbz files on a regular HD.
Increasing the "SyzygyProbeDepth" option lets the engine probe less aggressively. Set this option to a higher value if you experience too much slowdown (in terms of nps) due to TB probing.
Set the "Syzygy50MoveRule" option to false if you want tablebase positions that are drawn by the 50-move rule to count as win or loss. This may be useful for correspondence games (because of tablebase adjudication).
The "SyzygyProbeLimit" option should normally be left at its default value.
What to expect If the engine is searching a position that is not in the tablebases (e.g. a position with 7 pieces), it will access the tablebases during the search. If the engine reports a very large score (typically 123.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 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 it yourself
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.
Resource For Understanding the Code Base
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Chess Programming Wiki has good overall chess engines explanations (techniques used here are well explained like hash maps etc), it was also recommended by the support team at stockfish.
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Here you can find a set of features and techniques used by stockfish and each of them is explained at the wiki, however, it's a generic way rather than focusing on stockfish's own implementation, but it will still help you.
Terms of use
Stockfish is free, and distributed under the GNU General Public License (GPL). 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 found in the file named Copying.txt.