Loop (Program)

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Loop, an UCI compliant chess engine by Fritz Reul with different board representations for 32-bit and 64-bit platforms, at times commercial. Loop became subject of its author's Ph.D. thesis New Architectures in Computer Chess. Despite different board representation, both Loop versions presumably share same search and evaluation with similar features and weights. = 32-bit Loop= The 32-bit program, based on Reul's former program List, relies on a 15x12 board representation in conjunction with disjoint piece-lists with adequate move generation of blocker loops. It participated as Loop Leiden at the DOCCC 2006, becoming strong runner up behind Rybka. A specially adapted version called Loop Express became the engine of Wii Chess for the Nintendo Wii console in 2008. The non-bitboard data-structure of Loop was also applied in Chrilly Donninger's chess machine Hydra.

Reul in his thesis : This computerchess architecture was first implemented in the quite successful computerchess engine Loop Leiden 2006. The computerchess architecture was later implemented partially in Hydra and completely in Wii Chess by Nintendo (see Section 2.1). The high performance was just as important for these projects as the simplicity and ease of implementation in the following two environments: (1) the environment of a sophisticated computer-chess machine (Hydra) and (2) the environment of a commercial games console with the highest quality and security standards.

=64-bit Loop= The bitboard based Loop applies Magic Bitboards for sliding piece attack generation. Further, iterative alpha-beta bounded static exchange evaluation was applied to Loop Amsterdam, also performing a parallel search for a quad-core processor, which played a strong WCCC 2007 in Amsterdam, and became Third, behind the later disqualified Rybka, and Zappa.

Fritz Reul on an essential reason of Loop's success in Amsterdam in his thesis : A complete computer-chess architecture based on hash functions and magic multiplications for the examination of bitboards is implemented in the computerchess engine Loop Amsterdam. This engine was able to reach the 3rd place at the 15th World Computer-Chess Championship, Amsterdam (NL) 2007. An essential reason for the success of this 64-bit computer-chess engine was the use of highly sophisticated perfect hash functions and magic multipliers for the computation of compound bit-patterns (bitboards) via perfect hashing.

=Evaluation=

Preliminary Considerations
Evaluation was only marginally covered in Reul's thesis. In Preliminary Considerations he mentioned discussions with Chrilly Donninger, Fabien Letouzey and Tord Romstad, and the exchange of source codes : This thesis also does not aim at the explicit consideration of known computer-chess architectures, such as Rotated Bitboards or the 0x88 representation. Many a reference used in this thesis is not available in a scientifically elaborate form. This includes personal conversations with programmers, and the exchange of source codes as well as discussions via email. In this way the contents of this thesis can be regarded to be on a state-of the-art level of the research and development in the field of the computer-chess architectures.

Fruit Evaluation Overlap
During the ICGA Investigations concerning the Rybka Controversy and evaluation overlaps, 64-bit Loop was inspected by Mark Watkins who found congruence with the evaluation of Fruit 2.1. As confirmed by David Levy, the ICGA has received a complaint on Loop by Fruit author Fabien Letouzey and an investigation has been started about this case, as already mentioned by Watkins in August 2011. =Complaints= ICGA President David Levy, May 09, 2014 The ICGA has received formal complaints against the Chess programs LOOP and THINKER, both of which have participated in the World Computer Chess Championship. LOOP was entered by Fritz Reul into the 2007 WCCC in Amsterdam. THINKER was entered into the 2010 WCCC in Kanazawa. ... Here we present extracts from the first section of each of Mark Watkins reports.

Loop “The version examined here is Loop 2007 (64-bit), which was released at approximately the same time as the WCCC. There is notable similarity to Fruit in the evaluation function (other components were not examined).” ... Based on the above mentioned reports by Mark Watkins the ICGA is convinced that, at the very least, both Fritz Reul and Kerwin Medina have a case to answer. Depending on how Reul and/or Medina respond to these allegations the ICGA might decide to conduct further investigations and/or take some form of strong sanctioning action against the programmers. However, the ICGA does not intend to proceed further along the route to strong sanctions for the time being, in order to give these programmers more time in which to make contact with the ICGA President and present their defence to the allegations. If either or both of these programmers fail to do so by December 31st 2014, or refuses to do so, the ICGA will disqualify them from all their results in ICGA events. In the meantime the ICGA has decided to suspend both Fritz Reul and Kerwin Medina from participation in all ICGA events until such time as they have made contact and offered a defence.

=See also=
 * Coiled
 * Iteration
 * Iterative Search
 * List
 * Wii Chess

=Publications=
 * Fritz Reul (2009). New Architectures in Computer Chess. Ph.D. Thesis
 * Fritz Reul (2010). Static Exchange Evaluation with αβ-Approach. ICGA Journal, Vol. 33, No. 1

=Forum Posts=

2005 ...

 * Loop List available soon by Fritz Reul, CCC, October 11, 2005
 * Re: Loop List commercially available soon by Günther Simon, CCC, October 11, 2005


 * Loop 13.6 soon available by Gerhard Sonnabend, CCC, April 20, 2007
 * doing undoing by Fritz Reul, CCC, May 14, 2007
 * Iterative DTS by Fritz Reul, CCC, July 02, 2007
 * Re: Bob Hyatt says that... by Mike Scheidl, CCC, August 29, 2008
 * Re: Bob Hyatt says that... by Uri Blass, CCC, August 30, 2008

2010 ...

 * Loop 2007 / Fruit 2.1 by BB+, OpenChess Forum, April 18, 2011 » Fruit
 * Loop as a Fruit clone by Rebel, Rybka Forum, September 20, 2013
 * Complaints against the Chess programs LOOP and THINKER by Harvey Williamson, Hiarcs Forum, May 12, 2014
 * Complaints against the Chess programs LOOP and THINKER by Harvey Williamson, CCC, May 14, 2014

2015 ...

 * Re: FIDE Rules on ICGA - Rybka controversy by BB+, OpenChess Forum, May 08, 2015

=External Links=

Chess Engine

 * List's ICGA Tournaments (covers Loop)
 * Loop at CCRL 40/40
 * Wii Chess from Wikipedia
 * ICGA/Rybka controversy: Feedback - Allegations against another Chess Engine – The LOOP Program by David Levy, ChessBase News, February 17, 2012
 * Allegations against two more Chess Engines – The LOOP Program by David Levy, ICGA president, May 22, 2012 » Thinker
 * Complaints against the Chess programs LOOP and THINKER by David Levy, ICGA President, May 9, 2014

Misc

 * Loop disambiguation page from Wikipedia
 * The Loop disambiguation page from Wikipedia
 * Looping disambiguation page from Wikipedia
 * Loop control flow from Wikipedia
 * For loop
 * Foreach loop
 * While loop
 * Do while loop
 * Infinite loop

=References= Up one level