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Home * Engines * Bison

American Bison [1]

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 [2], might be subject of scientific research - opposed to the Rybka Controversy, both sources are freely availably [3] [4].


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.


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 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 [5]

[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

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External Links

Chess Engine


Extant Bison

Plains bison from Wikipedia
Wood bison from Wikipedia

Extinct Bison


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