Crate retroboard

rs-Retroboard

A chess retrograde move generator. Rust port of Retroboard. Suitable for endgame tablebase generation.

Status

Strong test suite but lack of comparaison of perft result against a trusted source.

Specification

En-passant is supported, but not castling. Legal but unreachable positions are supported (mainly positions with too many checkers).

Examples of accepted unreachable positions:

• 8/4k3/3B1B2/8/8/8/8/4K3 b - - 0 1 Impossible check
• 8/8/R4k2/4p3/8/8/8/4K3 b - e6 0 1 Impossible en passant square. e7e5 would have been illegal because black already in check.

It aims to follow the same generation rules as used by the generation software of syzygy and Gaviota tablebase.

Performance

A very rough perft test at depth 4 on this position gives 88148797 moves in ~2s (tested on Apple M1). That is roughly 3.5x times slower than shakmaty crate, but is ought to be improved.

fen : q4N2/1p5k/3P1b2/8/6P1/4Q3/3PB1r1/2KR4 b - - 0 1, with 2PNBRQ in white pocket, 3NBRQP in black one, Q uncastling and allowing en-passant moves.

Example

use retroboard::RetroBoard;

let r = RetroBoard::new_no_pockets("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1").unwrap();
assert_eq!(r.legal_unmoves().len(), 4);

Modules

shakmaty

Using the re-exported version of shakmaty will ensure no version clashes

Structs

ParseRetroPocketError

Error when parsing an invalid retro UCI.

RetroBoard

A shakmaty::Board where Unmove are played and all legal Unmove can be generated. It is the user responsability to ensure that position is legal. Unreachable positions are considered legal, for example this position.

RetroPocket

A RetroBoard pocket with a counter for each piece type. It stores the pieces than can be uncaptured by each color.
self.unpromotion is the number of pieces than can unpromote into a pawn. By default it is set to 0

RetroPockets

Wrapper around RetroPocket that provide handful functions to access them by color

UnMove

Information about a move.

Enums

MoveKind

Enum representing the different kind of type an UnMove can be.

Functions

perft

From shakmaty code source Counts legal move paths of a given length.

Type Aliases

UnMoveList

A container for unmoves that can be stored inline on the stack.