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Frank-Walter meets Condoleezza ^[1]

FrankWalter, (Frank Walter, Frank-Walter)
a Chess Engine Communication Protocol compliant open source chess engine by Laurens Winkelhagen, written in Java, licensed under the GPL v3.0. After continuing the development on his old engine ^[2], Laurens Winkelhagen re-published FrankWalter 2.2.0 in November 2018 ^[3], short before it had its over the board debut at the PT 54 in Leiden.

Etymology

Frank-Walter Steinmeier, in 2009 German Minister for Foreign Affairs, since March 2017 President of Germany, and his apparently desired name change ^[4] to Frank was the inspiration for the name of the chess engine ^[5]. Frank-Walter Steinmeier in an 2011 interview ^[6]

Mr. Steinmeier, can you actually play chess, like Peer Steinbrück and Helmut Schmidt?

Frank-Walter Steinmeier: Neither am I a good chess player nor am I currently writing a book.

Features

FrankWalter represents the board using a two-dimensional array of piece bitboards, indexed by color and type, and further has an 8x8 board for a square-centric view. These are all members of a board class along with the usual stuff specifying a chess position, such as side to move, castling rights, en passant target, halfmove clock, and an array of Zobrist keys to detect repetitions along the actual game record and variation. Despite sliding piece attacks are determined by a memory friendly approach of Kindergarten bitboards for files and Magic bitboards for ranks and bishops, FrankWalter keeps attack tables in classical Chess 4.5 style ^[7], that is two bitboard arrays (ATKFR and ATKTO) indexed by square, While along with keeping bitboards for pinned pieces, this seems an reasonable approach to implement legal move generation, the culprit is the incremental update, in particular using a copy-make stack to copy the 1K attack table not only during make but also back during unmake ^[8].