Bison

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Bison, an UCI compliant open source chess engine by Ivan Bonkin, written in C++ and licensed under GPLv3. Bison played the CCCCISC 2008 over the board. Whether Bison is merely a rewrite of the Fruit concepts, using bitboards instead of vector attack arrays, as suggested by Dann Corbit , might be subject of scientific research - opposed to the Rybka Controversy, both sources are freely availably .

=Description=

Board Representation
Bison is a bitboard engine and uses rotated bitboards to determine sliding piece attacks. It performs the 2x32-bit SWAR-implementation to count populations, and De Bruijn multiplication to scan bits forward in bitboard serialization.

Search
Bison applies PVS alpha-beta with transposition table, null move pruning with zugzwang verification search, razoring, IID, futility pruning, history pruning, delta pruning and mate distance pruning, LMR and various extensions inside an iterative deepening framework with aspiration windows and floating point fractional ply depths. SEE is used in move ordering and to determine winning tactical moves in quiescence.

Evaluation
Evaluation is sped up by pre-initialized material-tables indexed à la Strelka and a pawn hash table and might be lazy. It otherwise takes pawn structure, mobility considering pinned pieces and king piece tropism and various pattern and attacks under account with focus on king safety and passed pawns, speculatively aggregating middlegame and endgame scores, which were tapered by a range of 24 game phases.

=Selected Games= CCCCISC 2008, round 3, Bison - Counter [Event "CIS 2008"] [Site "Moscow SDCHESS RGSU"] [Date "2008.03.01"] [Round "3"] [White "Bison 8.2.4r"] [Black "Counter 0.8"] [Result "1/2-1/2"]

1.Nf3 d5 2.d4 Nf6 3.c4 e6 4.Nc3 Be7 5.Bg5 h6 6.Bh4 O-O 7.e3 b6 8.Rb1 c6 9.cxd5 exd5 10.Bd3 Bg4 11.O-O Ne4 12.Bxe7 Qxe7 13.Qc2 Bxf3 14.gxf3 Nxc3 15.Qxc3 a5 16.Rbc1 Rc8 17.Kh1 Qf6 18.Be2 Nd7 19.Qb3 a4 20.Qa3 c5 21.dxc5 Rxc5 22.b4 Rxc1 23.Qxc1 Qe6 24.Qc2 Ne5 25.Rc1 a3 26.Qd2 Nc6 27.b5 Ne7 28.Rc3 Qd6 29.Qd4 Rc8 30.Rxc8+ Nxc8 31.Bd3 Qc5 32.Qh4 Ne7 33.Kg2 f6 34.Qa4 Kf7 35.Be2 Qc3 36.Bd1 g6 37.Qa7 Qc4 38.Bb3 Qxb5 39.e4 Qc5 40.Bxd5+ Kg7 41.Qd7 h5 42.Be6 Qg5+ 43.Kh3 Qc5 44.f4 g5 45.fxg5 fxg5 46.Bd5 g4+ 47.Kg2 Kh6 48.Qe6+ Ng6 49.Qf6 h4 50.h3 gxh3+ 51.Kxh3 Qc1 52.Qf3 Qg5 53.Bb3 Nf4+ 54.Kh2 b5 55.Kh1 Kg6 56.Bc2 Kf6 57.Qc3+ 1/2-1/2

=Forum Posts=

2008 ...

 * Is Bison kosher ? by Olivier Deville, CCC, February 05, 2008
 * Bison 8.2.4r : 2152 by Patrick Buchmann, CCC, February 07, 2008
 * Bison 9.6 is released... by Dr.Wael Deeb, CCC, June 10, 2009
 * Bison 9.6 : 2507 by Patrick Buchmann, CCC, June 12, 2009
 * Bison Info by Ted Summers, CCC, June 19, 2009
 * Bison 9.8 : 2528 by Patrick Buchmann, CCC, August 02, 2009
 * Bison 9.11 is released... by Dr.Wael Deeb, CCC, November 22, 2009
 * Bison 9.11 : 2585 by Patrick Buchmann, CCC, November 23, 2009

2010 ...

 * Bison by Graham Banks, Winboard Forum, March 04, 2010
 * About derivatives by Olivier Deville, OpenChess Forum, August 11, 2011

=External Links=

Chess Engine

 * Bison at SourceForge.net
 * Bison by Иван Бонькин (Ivan Bonkin), Russia! from sdchess.ru
 * Bison in CCRL 40/15

Misc

 * Bison from Wikipedia
 * Bison (disambiguation) from Wikipedia
 * Bison - Wikispecies
 * GNU bison from Wikipedia
 * Bison - GNU parser generator

Extant Bison

 * American bison from Wikipedia
 * Plains bison from Wikipedia
 * Wood bison from Wikipedia


 * European bison from Wikipedia

Extinct Bison

 * Bison antiquus from Wikipedia
 * Bison latifrons from Wikipedia
 * Bison occidentalis from Wikipedia
 * Steppe bison from Wikipedia

=References= Up one Level