-### Overview
+## Overview
[](https://travis-ci.org/official-stockfish/Stockfish)
-[](https://ci.appveyor.com/project/mcostalba/stockfish)
+[](https://ci.appveyor.com/project/mcostalba/stockfish/branch/master)
-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](https://stockfishchess.org) 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.
-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
+## 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.
+ * Copying.txt, a text file containing the GNU General Public License version 3.
* src, a subdirectory containing the full source code, including a Makefile
that can be used to compile Stockfish on Unix-like systems.
-### Syzygybases
+## UCI parameters
+
+Currently, Stockfish has the following UCI options:
+
+ * #### Debug Log File
+ Write all communication to and from the engine into a text file.
+
+ * #### Contempt
+ A positive value for contempt favors middle game positions and avoids draws.
+
+ * #### 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.
+
+ * #### Threads
+ The number of CPU threads used for searching a position. For best performance, set
+ this equal to the number of CPU cores available.
+
+ * #### Hash
+ The size of the hash table in MB. It is recommended to set Hash after setting Threads.
+
+ * #### Clear Hash
+ Clear the hash table.
+
+ * #### Ponder
+ Let Stockfish ponder its next move while the opponent is thinking.
+
+ * #### MultiPV
+ Output the N best lines (principal variations, PVs) when searching.
+ Leave at 1 for best performance.
+
+ * #### Skill Level
+ Lower the Skill Level in order to make Stockfish play weaker (see also UCI_LimitStrength).
+ Internally, MultiPV is enabled, and with a certain probability depending on the Skill Level a
+ weaker move will be played.
+
+ * #### UCI_LimitStrength
+ Enable weaker play aiming for an Elo rating as set by UCI_Elo. This option overrides Skill Level.
+
+ * #### UCI_Elo
+ If enabled by UCI_LimitStrength, aim for an engine strength of the given Elo.
+ This Elo rating has been calibrated at a time control of 60s+0.6s and anchored to CCRL 40/4.
+
+ * #### UCI_ShowWDL
+ If enabled, show approximate WDL statistics as part of the engine output.
+ These WDL numbers model expected game outcomes for a given evaluation and
+ game ply for engine self-play at fishtest LTC conditions (60+0.6s per game).
+
+ * #### 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.
+
+ * #### Slow Mover
+ Lower values will make Stockfish take less time in games, higher values will
+ make it think longer.
-**Configuration**
+ * #### nodestime
+ Tells the engine to use nodes searched instead of wall time to account for
+ elapsed time. Useful for engine testing.
-Syzygybases are configured using the UCI options "SyzygyPath",
-"SyzygyProbeDepth", "Syzygy50MoveRule" and "SyzygyProbeLimit".
+ * #### UCI_Chess960
+ An option handled by your GUI. If true, Stockfish will play Chess960.
-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 ":".**
+ * #### UCI_AnalyseMode
+ An option handled by your GUI.
-Example: `C:\tablebases\wdl345;C:\tablebases\wdl6;D:\tablebases\dtz345;D:\tablebases\dtz6`
+ * #### 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 ":".
-It is recommended to store .rtbw files on an SSD. There is no loss in
-storing the .rtbz files on a regular HD.
+ Example: `C:\tablebases\wdl345;C:\tablebases\wdl6;D:\tablebases\dtz345;D:\tablebases\dtz6`
-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.
+ It 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.
-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).
+ * #### 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.
-The "SyzygyProbeLimit" option should normally be left at its default value.
+ * #### 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.
+
+ * #### SyzygyProbeLimit
+ Limit Syzygy tablebase probing to positions with at most this many pieces left
+ (including kings and pawns).
+
+
+## What to expect from Syzygybases?
-**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
+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
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
+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
needed for optimal play and in addition being able to take into account
the 50-move rule.
+## Large Pages
+
+Stockfish supports large pages on Linux and Windows. Large pages make
+the hash access more efficient, improving the engine speed, especially
+on large hash sizes. Typical increases are 5..10% in terms of nps, but
+speed increases up to 30% have been measured. The support is
+automatic. Stockfish attempts to use large pages when available and
+will fall back to regular memory allocation when this is not the case.
+
+### Support on Linux
+
+Large page support on Linux is obtained by the Linux kernel
+transparent huge pages functionality. Typically, transparent huge pages
+are already enabled and no configuration is needed.
+
+### Support on Windows
+
+The use of large pages requires "Lock Pages in Memory" privilege. See
+[Enable the Lock Pages in Memory Option (Windows)](https://docs.microsoft.com/en-us/sql/database-engine/configure-windows/enable-the-lock-pages-in-memory-option-windows)
+on how to enable this privilege. Logout/login may be needed
+afterwards. Due to memory fragmentation, it may not always be
+possible to allocate large pages even when enabled. A reboot
+might alleviate this problem. To determine whether large pages
+are in use, see the engine log.
+
+## Compiling Stockfish yourself from the sources
+
+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.
+
+```
+ cd src
+ make help
+ make build ARCH=x86-64-modern
+```
+
+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.
+
+When reporting an issue or a bug, please tell us which version and
+compiler you used to create your executable. These informations can
+be found by typing the following commands in a console:
+
+```
+ ./stockfish
+ compiler
+```
+
+## 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.
-### Compiling it yourself
+### Donating hardware
-On Unix-like systems, it should be possible to compile Stockfish
-directly from the source code with the included Makefile.
+Improving Stockfish requires a massive amount of testing. You can donate
+your hardware resources by installing the [Fishtest Worker](https://github.com/glinscott/fishtest/wiki/Running-the-worker:-overview)
+and view the current tests on [Fishtest](https://tests.stockfishchess.org/tests).
-Stockfish has support for 32 or 64-bit CPUs, the hardware POPCNT
-instruction, big-endian machines such as Power PC, and other platforms.
+### Improving the code
-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.
+If you want to help improve the code, there are several valuable resources:
-### Resource For Understanding the Code Base
+* [In this wiki,](https://www.chessprogramming.org) many techniques used in
+Stockfish are explained with a lot of background information.
-* [Chess Programming Wiki](https://chessprogramming.wikispaces.com) 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.](http://support.stockfishchess.org/discussions/questions/1132-how-to-understand-stockfish-sources)
+* [The section on Stockfish](https://www.chessprogramming.org/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.
-* [Here](https://chessprogramming.wikispaces.com/Stockfish) 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.
+* The latest source can always be found on [GitHub](https://github.com/official-stockfish/Stockfish).
+Discussions about Stockfish take place in the [FishCooking](https://groups.google.com/forum/#!forum/fishcooking)
+group and engine testing is done on [Fishtest](https://tests.stockfishchess.org/tests).
+If you want to help improve Stockfish, please read this [guideline](https://github.com/glinscott/fishtest/wiki/Creating-my-first-test)
+first, where the basics of Stockfish development are explained.
-### Terms of use
+## 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
+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
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
+For full details, read the copy of the GPL v3 found in the file named
*Copying.txt*.
projects / stockfish / blobdiff