EXchess

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EXchess, (Experimental Chess Program) a Chess Engine Communication Protocol compatible experimental open source chess engine by Daniel Homan, written in C++, released under the GNU Public License. EXchess may optionally use an own GUI based on the Fast Light Tool Kit (FLTK).

=Board Representation= EXchess utilizes an 8x8 Board and piece lists as demonstrated in its move generation routine : struct square { char type;            // type of piece (0 - 6) char side;            // side which owns square (1 = white) };

struct position { square sq[64]; ...  char plist[2][7][10]; ... };

void position::allmoves(move_list *list, tree_search *ts) { ...  for(i=1;i<=plist[wtm][PAWN][0];i++) pawn_moves(list, plist[wtm][PAWN][i], ts); for(i=1;i<=plist[wtm][KNIGHT][0];i++) knight_moves(list, plist[wtm][KNIGHT][i], ts); ... }

=Search= The ches engine performs advanced search algorithms including principle variation search, null move, null move verification, dynamic search extensions, futility pruning, hash tables, history tables, quiescence search, and a material swap function. =Lazy SMP= Daniel Homan in July 2013 on his Lazy SMP implementation and work sharing : I changed the work-sharing approach to Lazy SMP in EXchess to be closer to the ABDADA model after Daniel Shawul's posts about his tests on the subject. However, I didn't want to use a hash table to keep a counter for the threads working on a given position. My hash table already had a 16 byte long entry, so I didn't want to expand it, and I also didn't like the idea of having to make each move before seeing whether another thread was searching it.

So as an alternative to the hash table, I made a simple work sharing data structure. In the end, it was just a single hash key for a position which is OR'd with the move being searched and the depth of the search. I use this to keep track of the move being searched at each ply of the tree for a given thread. Then, before I search a move at a given ply, I can just check the same ply in the other threads to see that the move is not already being worked on at that depth. If it is, then the move get placed at the end of the move list to be searched last. This doesn't allow for transpositions, but I expected the most likely work collisions to be as the threads are walking the PV where they will initially all be the same. Indeed, this scheme only helps in the PV, and if I check for work sharing in non-PV nodes, it only slows things down a bit.

My previous Lazy SMP work sharing was just to alternate moves (odd-even) in the root node for the odd-even threads. The above approach is about 10% faster than my previous scheme, and I get a time-to-depth improvement of roughly 1.65 for 2 threads compared to 1 thread and roughly 2.5 for 4 threads compared to 1 thread. Maybe not quite as good as ABDADA with a hash table counter, but not too bad for the simplicity.

=TD-leaf= EXchess applies evaluation learning using the Temporal Difference Learning (TD-leaf).

=Forum Posts=

1998 ...

 * New version of EXchess released by Dan Homan, CCC, April 08, 1998
 * EXchess 2.37 by Dan Homan, CCC, June 13, 1998
 * New EXchess Version by Dan Homan, CCC, November 02, 1998
 * EXchess pre-release testers sought by Dan Homan, CCC, December 13, 1999

2000 ...

 * version 3.14 of EXchess released by Dan Homan, CCC, May 02, 2000
 * New version of EXchess by Dan Homan, CCC, November 18, 2000
 * EXchess v4.02 released by Dan Homan, CCC, April 10, 2001
 * Wb2UCI and Problems with ExChess4.03a and GnuChess4.0.8 by Arturo Ochoa, Winboard Forum, July 24, 2003 » Wb2UCI, InBetween

2005 ...

 * New Version of EXchess by Dan Homan, CCC, Januaray 29, 2006
 * Insanity... or Tal style? by Miguel A. Ballicora, CCC, April 01, 2009 (refers EXchess) » Automated Tuning

2010 ...
2012 2013 2014
 * EXchess v6.01 by Daniel Homan, CCC, December 29, 2011
 * EXchess v6.10 released by Daniel Homan, CCC, January 29, 2012 » CLOP
 * EXchess v6.50 released by Daniel Homan, CCC, August 19, 2012
 * EXchess v6.70 released by Daniel Homan, CCC, December 20, 2012
 * Lazy SMP, part 2 by Daniel Homan, CCC, January 12, 2013 » Lazy SMP
 * EXchess v7.01 Released by Daniel Homan, CCC, March 10, 2013
 * EXchess v7.02 released by Daniel Homan, CCC, March 16, 2013
 * EXchess v7.03 released (bugfix + speed improved version by Daniel Homan, CCC, March 29, 2013
 * EXchess v7.11 released by Daniel Homan, CCC, June 27, 2013
 * Lazy SMP and Work Sharing by Daniel Homan, CCC, July 03, 2013 » Lazy SMP
 * EXchess v7.17 released by Daniel Homan, CCC, September 14, 2013
 * EXchess v7.26 released by Daniel Homan, CCC, May 07, 2014
 * EXchess v7.31 released by Daniel Homan, CCC, August 17, 2014
 * EXchess v7.51 released by Daniel Homan, CCC, December 26, 2014

2015 ...
2016
 * EXchess v7.71 released by Daniel Homan, CCC, May 29, 2015
 * EXchess v7.88 Released by Daniel Homan, CCC, December 30, 2015
 * EXchess v7.91 released by Daniel Homan, CCC, May 10, 2016
 * EXchess v7.92 released by Daniel Homan, CCC, May 11, 2016

2017
 * EXchess v7.92 and AMD Processors by Daniel Homan, CCC, October 08, 2016
 * EXchess v7.96 by Daniel Homan, CCC, January 31, 2017
 * EXchess v7.97 by Daniel Homan, CCC, February 04, 2017

=External Links=
 * Experimental Chess Program
 * EXchess in CCRL 40/40

=References= Up one Level