NoraGrace

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NoraGrace Logo 1 NoraGrace Logo ¹

Logo by Graham Banks from a picture of Nora Grace Oldre's footprints, Release Release 1.0 of the NoraGrace Chess Engine · ericoldre/NoraGrace-Chess · GitHub, NoraGraceV10.zip/NoraGrace.png, Re: Some others chess engines written in C# by Eric Oldre, CCC, June 29, 2014↩︎

NoraGrace,
a WinBoard compliant open source chess engine by Eric Oldre, written in C# and first released in June 2014 under the MIT License. NoraGrace evolved from a C# port of Sinobyl ¹, and is dedicated to Nora Grace Oldre who was taken from Eric and his wife unexpectedly a few days before she was due to be born ² ³ .

Contents

Description

Board Representation

Like Sinobyl, NoraGrace relies on bitboards, and further has an 8x8 mailbox. It uses magic bitboards to determine sliding piece attacks - factors were calculated from sparse 64-bit randoms. BitScan is implemented via 32-bit De Bruijn multiplication to conditionally branch on low and high double words. Bitboard serialization applies the C# yield statement ⁴, which is further used in various move generation routines. NoraGrace's square mapping has ranks from 8 to 1 mapped to 0-7 at the big-end over files from 'a' to 'h', square zero is a8: NoraGrace's BERLEF Mapping

Search

NoraGrace applies negamax alpha-beta with transposition table and quiescence search inside an iterative deepening framework with aspiration windows, enhanced by adaptive null move pruning with verification search in the endgame, extensions if SEE > 0 for checks and pawns to 7th rank, futility pruning and LMR.

Evaluation

Evaluation takes game phases into account, using a tapered eval along with PhasedScore objects, interpreting the low and high 32-bit double words of a 64-bit long as two SIMD integers of an endgame and opening score. Beside other features, NoraGrace considers material, piece-square tables, king safety, cached pawn structure and mobility.