shunsai

Fast shogi legal move generator — SHogi's Ultra-fast Next-gen Successor, for AI.

shunsai generates the legal moves of a shogi position, as fast as it can be made to. It is built on shogi_core for the fundamental types and re-exports it, so a consumer needs no separate version of it.

Everything it generates is fully legal, pawn-drop mate (打ち歩詰め) included, so a caller never filters what it is handed. That is checked against the known perft values through depth 6 on the initial position, and differentially against shogi_legality_lite on random playouts.

The API is pre-1.0 and can still change between minor versions.

Usage

[dependencies]
shunsai = "0.1"

use shunsai::Position;

let position = Position::startpos();
assert_eq!(position.legal_moves().len(), 30);

legal_moves() allocates. The fast path is generate_moves, which yields one MoveSet per origin with the destinations still packed as a bitboard — so code that only counts them never builds a Move, and can stop early by returning ControlFlow::Break. Moves are played and taken back with do_move and undo_move, which maintain a Zobrist key() incrementally; do_move returns an Undo the caller holds and hands back, so a Position owns nothing on the heap.

The API documentation has the rest, and examples/search.rs is a fixed-depth alpha-beta written on the public API alone.

Minimum supported Rust version: 1.88.

Scope

Legal move generation and position management. That is the whole crate.

Kifu I/O (SFEN/USI/KIF/CSA), evaluation functions, search, and tsume (mate) solvers are out of scope and belong in a crate that depends on this one — which is what shunsai is for. It is the foundation for a search engine, and through it a strong shogi AI.

Speed is the point, and it is settled by measurement rather than by argument: the method, the fixtures and where the crate currently stands are in BENCHMARKS.md.

The name

shunsai = 旬菜 (しゅんさい).

旬菜 means "seasonal vegetables at their peak" — the freshest produce of the season — continuing the culinary line of yasai (野菜, "vegetables").
At the same time it is a homophone of 俊才/駿才 — "a swift prodigy": the 俊 of 俊足 (swift-footed) and the 駿 of 駿馬 (a fleet steed). Speed is built into the sound of the name.
It ends in "ai". As a backronym: SHogi's Ultra-fast Next-gen Successor, for AI.

The project's record

DESIGN.md — scope, milestones, and the licensing policy
DECISIONS.md — what was decided and rejected, and what is still open
BENCHMARKS.md — how measurement is done, and every recorded number

License

MIT OR Apache-2.0, at your option.