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=Special Generators=
Most programs use special move generators for the [[Quiescence Search|quiescence search]], sometimes supplemented by one for getting out of [[Check|check]]. These special cases can be made more efficient than generating and testing each possible move to fit specific criteria. For example, if the king is in check, the only possible legal moves are to capture the attacking piece, block the attacker if it is a "ray" piece, or move the king to safety. Special generators for the quiescence search might want to generate checks in addition to [[Captures|captures]] and [[Promotions|promotions]]. They can use the fact that a knight or bishop must start off on the [[Color of a Square#SameColor|same color square]] as the opponent king if they are to attack it. And rooks can only generate at most 2 checking moves...to the [[Intersection Squares|squares]] with the rook's column and the king's row or the king's column and the rooks row.
Similar tricks can be used for generating possible moves out of check, which must be by the king, capturing the opponent's checking piece, or blocking its attack if it is a ray piece. When in [[Double Check|double check]], only king moves are permitted.
=Chunk move generationMove Generation=
With [[Move Ordering|move ordering]] in mind, chess programs, while traversing pieces and their move-target sets once, store and buffer generated moves inside one or two [[Move List|move lists]] (i.e. for [[Tactical Moves|tactical]] and [[Quiet Moves|quiet moves]]), which is convenient for book-keeping and assigning scores based on [[MVV-LVA]], [[Static Exchange Evaluation|SEE]], [[History Heuristic|history]], [[Piece-Square Tables|piece square table]] etc., to later perform a [https://en.wikipedia.org/wiki/Selection_sort selection sort] before actually [[Make Move|making the move]].
<span id="Staged"></span>
=Staged move generationMove Generation=
Some programs do not generate all moves at once, but do it in several stages (i.e. [[Hash Move|hash move]] first, then [[Captures|captures]], then [[Killer Move|killer moves]], then all the rest in a chunk) on the premise that if one of the early moves causes a cutoff, then we may save on the effort of generating the rest of the moves <ref>[http://www.talkchess.com/forum/viewtopic.php?t=27657 Move generation: staged vs all-at-once] by [[Steven Edwards]], [[CCC]], April 30, 2009</ref>.
=Debugging=
It is important to ensure that the move generator works properly. Although this could be tested by playing many games, a better approach is to write a [[Perft]] function. This function [[Recursion|recursively]] generates moves for the current position and all children up to a certain depth, and by counting all the leaf nodes, it can be compared to a [[Perft Results|table of values]] to test its accuracy.
<span id="Reverse"></span>
=Un-Move Generation=
'''Un-Move Generation''' produces a list of all possible moves (including [[Captures|captures]] and [[Promotions|promotions]]) which could be [[Unmake Move|un-made]] from a target position to reach all possible legal predecessor or parent positions for [[Retrograde Analysis|retrograde analysis]] tasks.
=See also=
* [[Joe Condon]], [[Ken Thompson]] ('''1982'''). ''Belle Chess Hardware'', [[Advances in Computer Chess 3]], Reprinted ('''1988''') in [[Computer Chess Compendium]]
* <span id="Waterloo1982"></span>[[Greg Bakker]], [[Jim Jonkman]], [[Jonathan Schaeffer]], [[Tom Schultz]] ('''1982'''). ''VLSI Implementation of a Chess Legal Move Generator''. EE755S-1, [[University of Waterloo]] <ref>[https://uwaterloo.ca/water-under-the-bridge/1983 1983 | Waking up to change] in [https://uwaterloo.ca/water-under-the-bridge/about-authors Chris Redmond and Simon the Troll] ('''1998'''). ''[https://uwaterloo.ca/water-under-the-bridge/ Water Under the Bridge]''. [[University of Waterloo]] » [[#Waterloo1982|VLSI Move Generation]]</ref>
* [[Jonathan Schaeffer]], [[Patrick A.D. Powell]], [[Jim Jonkman]] ('''1983'''). ''[https://link.springer.com/chapter/10.1007/978-3-642-95432-0_19 A VLSI legal move generator for the game of chess]''. in [https://en[Mathematician#REBryant|Randal E.wikipedia.org/wiki/Randal_Bryant Randal Bryant]] (eds.) [https://link.springer.com/book/10.1007%2F978-3-642-95432-0 Third Caltech Conference on Very Large Scale Integration]
* [[Carl Ebeling]], [[Andrew James Palay]] ('''1984'''). ''The Design and Implementation of a VLSI Chess Move Generator''. Proceedings of the 11th Annual International Symposium on Computer Architecture. [[IEEE]] and [[ACM]].
* [[Stuart Cracraft]] ('''1984'''). ''Bitmap move generation in Chess''. [[ICGA Journal#7_3|ICCA Journal, Vol. 7, No. 3]]
* [http://www.open-aurec.com/wbforum/viewtopic.php?f=4&t=331 Move Generation Speed] by [[Dan Honeycutt]], [[Computer Chess Forums|Winboard Forum]], October 21, 2004
==2005 ...==
* [http://www.open-aurec.com/wbforum/viewtopic.php?f=4&t=5623 Yet another new bitboard move generation method] by [[Zach Wegner]], [[Computer Chess Forums|Winboard Forum]], September 22, 2006 » [[Titboards]]
: [http://www.open-aurec.com/wbforum/viewtopic.php?f=4&t=5623&start=6 Re: Yet another new bitboard move generation method] by [[Harm Geert Muller]], [[Computer Chess Forums|Winboard Forum]], October 01, 2006 <ref>[http://www.talkchess.com/forum3/viewtopic.php?f=7&t=52861&start=8 Re: multi-dimensional piece/square tables] by Tony P., [[CCC]], January 28, 2020</ref>
* [http://www.talkchess.com/forum/viewtopic.php?t=17790 Is it time for another new move generator?] by [[Michael Sherwin]], [[CCC]], November 11, 2007
* [http://www.talkchess.com/forum/viewtopic.php?t=17820 Did someone mention the GNUChess move Generator?] by [[Michael Sherwin]], [[CCC]], November 12, 2007 » [[GNU Chess]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=19837 compact bitboard move generator] by [[Robert Hyatt]], [[CCC]], February 25, 2008 » [[Bitboard Serialization]]
* [http://www.talkchess.com/forum/viewtopic.php?t=20630 Move generator] by [[Chua Kong Sian|kongsian]], [[CCC]], April 12, 2008
* [http://www.talkchess.com/forum/viewtopic.php?t=25917 Bitboards / move generation on larger boards] by [[Gregory Strong]], [[CCC]], January 09, 2009
* [http://www.talkchess.com/forum/viewtopic.php?t=54465 Black/White symmetry in move generation] by Jeffery A Esposito, [[CCC]], November 25, 2014 » [[Color Flipping]]
* [http://www.talkchess.com/forum/viewtopic.php?t=54704 Symmetric move generation using bitboards] by [[Lasse Hansen]], [[CCC]], December 20, 2014
* [http://www.talkchess.com/forum/viewtopic.php?t=54796 Reverse move generation] by Kostas Oreopoulos, [[CCC]], December 30, 2014 » [[Move Generation#Reverse|Un-Move Generation]], [[Retrograde Analysis]]
==2015 ...==
* [http://www.talkchess.com/forum/viewtopic.php?t=55275 On bitboard legal move generation] by [[Lasse Hansen]], [[CCC]], February 09, 2015
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=70082 Opinions requested for new move gen idea] by [[Michael Sherwin]], [[CCC]], March 03, 2019 » [[Table-driven Move Generation]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=70508 My newest almost bb move generator is wonderful] by [[Michael Sherwin]], [[CCC]], April 17, 2019
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=70515 Efficient capture generation in the game of Thud] by koedem, [[CCC]], April 18, 2019
==2020 ...==
* [http://www.talkchess.com/forum3/viewtopic.php?f=2&t=74917 Comparing 4 move generators: 0x88 vs 10x12 vs 10x12 + bitboards HYBRID vs Pure MAGIC BITBOARDS] by [[Maksim Korzh]], [[CCC]], August 28, 2020
'''2021'''
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=76835 Staged move generation?] by [[Niels Abildskov]], [[CCC]], March 10, 2021 » [[Move Generation#Staged|Staged Move Generation]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=77350 Being silly with perft and legal move generation] by [[Jakob Progsch]], [[CCC]], May 19, 2021 » [[Perft]], [[#Legal|Legal Move Generation]], [[En passant]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=77465 Advice on optimizing my move generation] by Christian Dean, [[CCC]], June 11, 2021
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=77671 Efficiently Generated Legal moves question] by Pedro Duran, [[CCC]], July 08, 2021 » [[Legal Move]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=77906 Move generator advice] by Ellie Moore, [[CCC]], August 08, 2021
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=78084 Legal or pseudolegal move generator?] by Pier Carlo, [[CCC]], September 03, 2021
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=78164 Distinguish rook and bishop move efficiently] by [[Guido Flohr]], [[CCC]], September 14, 2021
* [https://www.talkchess.com/forum3/viewtopic.php?f=7&t=78913 Fast reverse move generation] by koedem, [[CCC]], December 18, 2021 » [[Move Generation#Reverse|Un-Move Generation]], [[Retrograde Analysis]]
: [https://www.talkchess.com/forum3/viewtopic.php?f=7&t=78913&start=1 Re: Fast reverse move generation] by [[Peter Österlund]], [[CCC]], December 18, 2021 » [[Texel]]
'''2022'''
* [https://www.talkchess.com/forum3/viewtopic.php?f=7&t=79365 Move generation for bitboards] by [[Elias Nilsson]], [[CCC]], February 16, 2022
=External Links=
* [http://www.chilton-computing.org.uk/acl/literature/books/gamesplaying/p003.htm Chapter 3: Board Games - 3.1 CHESS] from [[Alex Bell]] ('''1972'''). ''[http://www.chilton-computing.org.uk/acl/literature/books/gamesplaying/overview.htm Games Playing with Computers]''. Allen & Unwin, ISBN-13: 978-0080212227
* [http://web.archive.org/web/20070716111804/www.brucemo.com/compchess/programming/0x88.htm Description of 0x88 method] from [[Bruce Moreland|Bruce Moreland's]] [http://web.archive.org/web/20070607231311/www.brucemo.com/compchess/programming/index.htm Programming Topics]([https://en.wikipedia.org/wiki/Wayback_Machine Wayback Machine])* [http://web.archive.org/web/20070715002634/www.brucemo.com/compchess/programming/movetable.htm Move Table move generation] from [[Bruce Moreland|Bruce Moreland's]] [http://web.archive.org/web/20070607231311/www.brucemo.com/compchess/programming/index.htm Programming Topics]([https://en.wikipedia.org/wiki/Wayback_Machine Wayback Machine])
* [http://john.stanback.net/zarkov/zarkov_methods.html How Zarkov Plays Chess] by [[John Stanback]]
* [http://perl.guru.org/scott/hobbies/chess/ Monsoon/Typhoon Homepage] by [[Scott Gasch]], covers [[0x88]] move generation
* [http://www.pradu.us/old/Nov27_2008/Buzz/ Buzz - A Winboard Chess Playing Program] by [[Pradu Kannan]] - Source of [[Magic Bitboards|magic]] Move Generator
* [httphttps://www.gamedev.net/page/resourcestutorials/_/technical/artificial-intelligence/chess-programming-part-iii-move-generation-r1126 / Chess Programming Part III: Move Generation] by [[François-Dominic Laramée]], [https://en.wikipedia.org/wiki/GameDev.net gamedev.net], July 2000* [httphttps://labraj.uni-mbferi.um.si/en/Chess_Move_Generator Chess Move Generator - Computer Architecture and Languages Laboratory], [[University of Maribor]]
* [https://sites.google.com/site/hispanicchessengines/programs--interface---engines/engine Engine - Hispanic Chess Engines | The move generator] by [[Pedro Castro]]
* [https://enpeterellisjones.wikipedia.orgcom/posts/wikigenerating-legal-chess-moves-efficiently/Generator_%28computer_programming%29 Generator (computer programming) from WikipediaGenerating Legal Chess Moves Efficiently] by [[Peter Ellis Jones]], February 09, 2017
=References=
<references />
'''[[Board Representation|Up one level]]'''
[[Category:Zollern]]
[[Category:Industrial Heritage Trail]]
