Fairy-Stockfish 13.1

This release adds support for up to 26 custom piece types per user-defined variant.

New

• Custom piece types
  • Piece movements are defined using Betza notation.
  • See the variants.ini for details on defining custom pieces.
• New base piece movements
  • Nightrider
  • Diagonal cannon
  • Grasshopper
  • Limited distance sliders
• Variants
  • Nightrider
  • Grasshopper
  • TenCubed
  • Yari, Tori, and Okisaki shogi

Improvements

• Small speed improvements for all variants
• Significant playing strength improvement in bughouse against human opponents by considering drops of pieces from anticipated piece flow.

Fixes

• Fix atomic castling rules for one corner case to ensure compatibility with lichess rules.
• Use correct rank numbering for en passant field in Grand chess FENs in CECP protocol.
• Disambiguate castling moves in variants where the king only moves one square to castle.

Files of the release

• .exe are Windows executables, the files without extensions are Linux binaries.
• Versions containing largeboard have support for board sizes >8x8 (e.g., Xiangqi, Shogi), the others are faster but have less variants.
• Use bmi2 versions for best performance on modern hardware, or fairy-stockfish-largeboard_x86-64.exe for best compatibility.
• The variants.ini contains documentation and examples how to configure user-defined variants and pieces.

Thanks to all code contributors, fishtest contributors, and supporters for their contributions to this release.