RedQueen

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RedQueen, an UCI compliant open source chess engine under the GNU General Public License, written in C++ by Ben-Hur Carlos Vieira Langoni Junior. Using minimal library dependencies as possible, it could easily ported to various operating systems such as Windows, Linux, Mac OS, and Android. The name RedQueen was inspired by the Red Queen character in Lewis Carroll's Through the Looking-Glass novel.

=Description=

Bitboards
RedQueen is a bitboard engine and uses Pradu Kannan's magic bitboards to determine sliding piece attacks. BitScans are either implemented in inline assembly for x86-64 processor instructions, or with De Bruijn multiplication and double conversion for forward and reverse scans respectively : const uint64_t debruijn64 = 0x07EDD5E59A4E28C2ULL; const uint32_t index64[64] = { 63, 0, 58,  1, 59, 47, 53,  2,   60, 39, 48, 27, 54, 33, 42,  3,   61, 51, 37, 40, 49, 18, 28, 20,   55, 30, 34, 11, 43, 14, 22,  4,   62, 57, 46, 52, 38, 26, 32, 41,   50, 36, 17, 19, 29, 10, 13, 21,   56, 45, 25, 31, 35, 16,  9, 12,   44, 24, 15,  8, 23,  7,  6,  5 };

inline int bitScanForward(int* const index, const uint64_t mask) { uint64_t ret; asm ("bsfq %[mask], %[ret]" : [ret] "=r" (ret) :[mask] "mr" (mask)); *index = int(ret); *index = int(index64[((mask & -mask) * debruijn64) >> 58]); return mask?1:0; } inline int bitScanReverse(int* const index, const uint64_t mask) { uint64_t ret; asm ("bsrq %[mask], %[ret]" :[ret] "=r" (ret) :[mask] "mr" (mask)); *index = (unsigned int)ret; union { double d;     struct { unsigned int mantissal : 32; unsigned int mantissah : 20; unsigned int exponent : 11; unsigned int sign : 1; };  } ud; ud.d = (double)(mask & ~(mask >> 32)); *index = ud.exponent - 1023; return mask?1:0; }
 * 1) if defined(__LP64__)
 * 1) else
 * 1) endif
 * 1) if defined(__LP64__)
 * 1) else
 * 1) endif

Similar holds for population count with SSE4 instruction if available versus SWAR-popcount, also using an optimized version for populations below 16, borrowed from Stockfish.

Search
RedQueen applies a parallel search considering the Young Brothers Wait Concept using a pool of threads where a master spawns idle threads. The search is PVS alpha-beta with the shared transposition table inside an iterative deepening framework with aspiration windows. Selectivity is applied by check and PV extensions, adaptive nullmove pruning, razoring, futility pruning, reductions at PV- and more aggressively at none PV-nodes. The SEE swap algorithm is used to prune bad captures in quiescence search, as well in move ordering, which is further improved by the obligatory killer- and history heuristics.

Evaluation
The evaluation might be lazy and otherwise considers tactical and positional features as well as material imbalances along with a pawn structure cache and a tapered eval interpolating middlegame and endgame scores with passed pawn and king safety and most dominant terms beside material.

=Tournament Play= Over the board, RedQueen played the ICT 2010, DOCCC 2010, ICT 2011, ICT 2012, PT 52, PT 53 and PT 54 CSVN tournaments in Leiden, online the ACCA 2010, ACCA 2011, CCT13, CCT14, and the WCRCC 2011.

=Selected Games= ACCA 2011, round 2, RedQueen - Crafty [Event "ACCA 2011"] [Site "HGM's server"] [Date "2011.11.12"] [Round "2"] [White "RedQueen"] [Black "Crafty"] [Result "1/2-1/2"]

1.c4 e6 2.Nf3 d5 3.d4 Nf6 4.Nc3 Be7 5.Bf4 O-O 6.e3 Nbd7 7.c5 Nh5 8.Bd3 Nxf4 9.exf4 c6 10.Qc2 g6 11.h4 Nf6 12.a3 b6 13.b4 Qc7 14.g3 a5 15.Na4 b5 16.Nb6 Ra7 17.O-O axb4 18.axb4 Rxa1 19.Rxa1 Bb7 20.Qe2 Nd7 21.Nxd7 Qxd7 22.Ne5 Qc7 23.h5 Bf6 24.Qg4 Re8 25.Ra7 Kf8 26.hxg6 hxg6 27.Nxf7 Qxf7 28.Bxg6 Qg7 29.Rxb7 Qxb7 30.Bxe8 Kxe8 31.Qxe6+ Be7 32.f5 Qd7 33.Qg8+ Bf8 34.Qg6+ Kd8 35.Qf6+ Be7 36.Qh8+ Qe8 37.Qe5 Kd7 38.Qe6+ Kd8 39.Qe5 Kd7 40.Qe6+ Kd8 41.Qe5 1/2-1/2

=See also=
 * Alice
 * Queen (engine)

=Forum Posts=

2010

 * RedQueen 0.6 by Ben-Hur Carlos Langoni, CCC, August 21, 2010
 * Redqueen v0.7 by Ben-Hur Carlos Langoni, CCC, October 18, 2010
 * Redqueen v0.7.5 (ACCA 2010) by Ben-Hur Carlos Langoni, CCC, November 08, 2010 » ACCA 2010
 * Redqueen v0.8 by Ben-Hur Carlos Langoni, CCC, December 01, 2010
 * Test position for average engines by Ben-Hur Carlos Langoni, CCC, December 06, 2010 » DOCCC 2010, Fridolin

2011

 * Redqueen v0.9 release by Ben-Hur Carlos Langoni, CCC, January 31, 2011
 * Redqueen v0.9.1 release by Ben-Hur Carlos Langoni, CCC, February 10, 2011
 * Redqueen v0.9.5 release by Ben-Hur Carlos Langoni, CCC, February 21, 2011
 * RedQueen for Android by Aart Bik, CCC, April 03, 2011
 * RedQueen v0.9.8 release by Ben-Hur Carlos Langoni, CCC, April 27, 2011
 * 2011 Fifth Annual ACCA WCRCC: RedQueen games by Ben-Hur Carlos Langoni, CCC, July 23, 2011 » WCRCC 2011
 * RedQueen 1.0 beta release by Ben-Hur Carlos Langoni, CCC, September 04, 2011
 * 2011 6ht annual ACCA games (RedQueen's games) by Ben-Hur Carlos Langoni, CCC, November 13, 2011 » ACCA 2011

2012 ...

 * RedQueen 1.1 released by Ben-Hur Carlos Langoni, CCC, March 15, 2012
 * RedQueen 1.1.1 (bugfix release) by Ben-Hur Carlos Langoni, CCC, March 15, 2012
 * RedQueen 1.1.1 on Mac OS X by Robert Purves, CCC, March 16, 2012
 * Redqueen 1.1.1 64-bit - Is this a bug? by Gabor Szots, CCC, March 26, 2012
 * Redqueen v1.1.98 Linux/Windows 64 bit edition by Norbert Raimund Leisner, {{CCC]], May 11, 2016
 * RedQueen for the Mac by MikeB, CCC, May 31, 2016

=External Links=

Chess Engine

 * RedQueen Chess Engine website
 * RedQueen | Chess Engine
 * RedQueen in CCRL 40/4

Misc

 * Red Queen (disambiguation) from Wikipedia
 * Red Queen (Through the Looking-Glass) - Wikipedia
 * Red Queen's race from Wikipedia


 * The Red Queen's Race from Wikipedia (Isaac Asimov)
 * Red Queen hypothesis from Wikipedia
 * Red Queen (comics) from Wikipedia
 * The Red Queen: Sex and the Evolution of Human Nature - Wikipedia
 * Gryphon - Checkmate, Red Queen to Gryphon Three (1974), YouTube Video

=References= Up one Level