Changes

an [[UCI]] compliant chess engine by [[Fritz Reul]] with different [[Board Representation|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'' <ref>[[Fritz Reul]] ('''2009'''). ''New Architectures in Computer Chess''. Ph.D. Thesisthesis</ref> . Despite different board representation, both Loop versions presumably share same [[Search|search]] and [[Evaluation|evaluation]] with similar features and weights.

The 32-bit program, based on Reul's former program [[List (Program)|List]], relies on a [[Vector Attacks#15x12|15x12 board]] representation in conjunction with disjoint [[Piece-Lists#NewArchitecture|piece-lists]] with adequate [[Move Generation|move generation]] of [[Vector Attacks#NewArchitecture|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 [https://en.wikipedia.org/wiki/Nintendo Nintendo] [https://en.wikipedia.org/wiki/Wii Wii] [https://en.wikipedia.org/wiki/Video_game_console console] in 2008 <ref>[[Fritz Reul]] ('''2009'''). ''New Architectures in Computer Chess'', Ph.D. Thesisthesis, 2.2.2 Nintendo Wii Chess, pp. 11</ref> . The non-bitboard data-structure of Loop was also applied in [[Chrilly Donninger|Chrilly Donninger's]] chess machine [[Hydra]] <ref>[[Fritz Reul]] ('''2009'''). ''New Architectures in Computer Chess'', Ph.D. Thesisthesis, 2.2.1 The Chess Machine Hydra, pp. 11</ref> .

Reul in his thesis <ref>[[Fritz Reul]] ('''2009'''). ''New Architectures in Computer Chess'', Ph.D. Thesisthesis, 5.1.1 Non-Bitboard Architectures, pp. 96</ref> :

The [[Bitboards|bitboard]] based Loop applies [[Magic Bitboards]] for [[Sliding Piece Attacks|sliding piece attack generation]]. Further, iterative [[Alpha-Beta|alpha-beta]] bounded [[Static Exchange Evaluation|static exchange evaluation]] was applied to ''Loop Amsterdam'' <ref>[[Fritz Reul]] ('''2010'''). ''Static Exchange Evaluation with αβ-Approach''. [[ICGA Journal#33_1|ICGA Journal, Vol. 33, No. 1]]</ref> , also performing a [[Parallel Search|parallel search]] for a quad-core processor, which played a strong [[WCCC 2007]] in [https://en.wikipedia.org/wiki/Amsterdam Amsterdam], and became Third, behind the later disqualified [[Rybka]], and [[Zappa]] <ref>[https://www.game-ai-forum.org/icga-tournaments/tournament.php?id=173 15th World Computer Chess Championship - Amsterdam 2007 (ICGA Tournaments)]</ref> .

Fritz Reul on an essential reason of Loop's success in Amsterdam in his thesis <ref>[[Fritz Reul]] ('''2009'''). ''New Architectures in Computer Chess'', Ph.D. Thesisthesis, 5.1.2 Magic Hash Functions for Bitboards, pp. 97</ref> :

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 <ref>[[Fritz Reul]] ('''2009'''). ''New Architectures in Computer Chess'', Ph.D. Thesisthesis, 1.2 Preliminary Considerations, pp. 3-4</ref> : This thesis also does not aim at the explicit consideration of known computer-chess architectures, such as [[Rotated Bitboards]] <ref>[[Stuart Cracraft]] ('''1984'''). ''Bitmap move generation in Chess''. [[ICGA Journal#7_3|ICCA Journal, Vol. 7, No. 3]]</ref> <ref>[[Robert Hyatt]] ('''1999'''). ''[http://www.cis.uab.edu/hyatt/bitmaps.html Rotated Bitmaps, a New Twist on an Old Idea]''. [[ICGA Journal#22_4|ICCA Journal, Vol. 22, No. 4]]</ref> or the [[0x88]] representation <ref>[http://web.archive.org/web/20070716111804/www.brucemo.com/compchess/programming/0x88.htm 0x88 Move Generation] by [[Bruce Moreland]]</ref>. Many a reference used in this thesis is not available in a scientifically elaborate form. This includes personal conversations with programmers <ref>[[Chrilly Donninger]] ('''2006'''). ''Discussion with Dr. Christian Donninger''.</ref>, <ref>[[Fabien Letouzey]] ('''2006'''). ''Personal discussion with Fabien Letouzey''.</ref> <ref>[[Tord Romstad]] ('''2007'''). ''Discussion with Tord Romstad''.</ref> , 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.

During the [[ICGA Investigations]] concerning the [[Rybka Controversy]] and [[Evaluation Overlap|evaluation overlaps]], 64-bit Loop was inspected by [[Mark Watkins]] who found congruence with the evaluation of [[Fruit|Fruit 2.1]] <ref>[http://www.open-chess.org/viewtopic.php?f=5&t=1353 Loop 2007 / Fruit 2.1] by [[Mark Watkins|BB+]], [[Computer Chess Forums|OpenChess Forum]], April 18, 2011</ref> . As confirmed by [[David Levy]] <ref> [httphttps://wwwen.chessbase.com/newsdetail.asp?newsid=7926 post/icga-rybka-controversy-feedback ICGA/Rybka controversy: Feedback - Allegations against another Chess Engine – The LOOP Program] by [[David Levy]], [[ChessBase|ChessBase News]], February 17, 2012</ref>, 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 <ref>[http://www.open-chess.org/viewtopic.php?f=5&t=1353#p13794 Re: Loop 2007 / Fruit 2.1] by [[Mark Watkins|BB+]], [[Computer Chess Forums|OpenChess Forum]], August 22, 2011</ref> .

[[ICGA]] President [[David Levy]], May 09, 2014 <ref>[https://icga.leidenuniv.nlorg/?p=919 Complaints against the Chess programs LOOP and THINKER] by [[David Levy]], [[ICGA]] President, May 9, 2014</ref>

* [[Fritz Reul]] ('''2009'''). ''New Architectures in Computer Chess''. Ph.D. Thesisthesis, [https://pure.uvt.nl/ws/portalfiles/portal/1098572/Proefschrift_Fritz_Reul_170609.pdf pdf]

* [https://icga.leidenuniv.nlorg/?p=354 Allegations against two more Chess Engines – The LOOP Program] by [[David Levy]], [[ICGA]] president, May 22, 2012 » [[Thinker]]* [https://icga.leidenuniv.nlorg/?p=919 Complaints against the Chess programs LOOP and THINKER] by [[David Levy]], [[ICGA]] President, May 9, 2014