RDChess

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RDChess, a free open source chess program by Rudolf Posch, written in Object Pascal with x86/MMX inline assembly. RDChess comes with an own Windows GUI, written in Delphi, and also has a WinBoard mode.

=Description=

Board Representation
The board is represented by a 12x12 mailbox array in conjunction with piece-lists. An attack table utilizes square control and a cheap SEE, and is calculated from scratch once per node - one byte per square and color in "ppbbrrqk" order, indicating which pieces control that square including bishop/rook x-rays through queen and king. The two-bit bb counter includes knight and bishop attacks. Strictly legal move generation requires determination of pinned pieces, also used in evaluation.

Search
The search applies NegaScout with TT, AEL-pruning, quiescence and various extensions inside an iterative deepening framework with aspiration windows. Move ordering considers hash move, re-captures, two killers, captures with positive SEE, quiet moves with priority from attacked squares to none attacked or defended squares, pawn moves, losing captures, and remaining.

Evaluation
Evaluation focuses on material balance with trade down bonus if ahead. Positional feature terms, considering pawn structure, piece development, king safety, hanging pieces, etc., rarely exceed the value of one pawn, except unstoppable passers in pawn endgames due to implementation of the rule of the square.

=Forum Posts=
 * Freeware chess program RDCHESS V2 by Rudolf Posch, CCC, May 31, 2001
 * Last Winboard engine updates: Comet B46 (Leiden) and RDChess v3.0. by Leo Dijksman, CCC, June 09, 2002

=External Links=
 * RDChess (Wayback Machine, March 09, 2005)
 * RDChess - RDChess Übersicht (German)
 * RDChess 3.23 in CCRL Blitz
 * RDChess 3.23 in KCEC
 * Schachclub Leinzell Schachprogramm RDChess by Peter Schreiner - Dezember 2001 (German)

=References= Up one Level