From 779f247bc84e0bf955f4e462d3d781b3ed79ca7f Mon Sep 17 00:00:00 2001
From: Bendik Samseth <b.samseth@gmail.com>
Date: Wed, 21 Aug 2024 09:23:15 +0200
Subject: [PATCH] Start implementing see
---
engine/src/movelist.rs | 147 +++++++++++++++++++++++++++++++++++++-
engine/src/search/cuts.rs | 1 +
2 files changed, 147 insertions(+), 1 deletion(-)
diff --git a/engine/src/movelist.rs b/engine/src/movelist.rs
index 37f9972..8378253 100644
--- a/engine/src/movelist.rs
+++ b/engine/src/movelist.rs
@@ -1,4 +1,4 @@
-use chess::{Board, ChessMove, MoveGen, Piece};
+use chess::{BitBoard, Board, ChessMove, Color, MoveGen, Piece};
use crate::chessmove::ChessMoveExt;
use crate::{newtypes::Value, opts::OPTS};
@@ -123,6 +123,97 @@ impl MoveVec {
self
}
+
+ pub fn see(board: &Board, capture: ChessMove) -> Value {
+ debug_assert!(capture.captures(board).is_some());
+
+ let initial_capture = capture
+ .captures(board)
+ .expect("should only call see on captures");
+ let target_square = capture.get_dest();
+ let initial_colour = board.side_to_move();
+ let mut blockers = board.combined() ^ BitBoard::from_square(capture.get_source());
+ let white_pieces = board.color_combined(Color::White);
+ let black_pieces = board.color_combined(Color::Black);
+
+ let mut attackers =
+ chess::get_king_moves(target_square) & blockers & board.pieces(Piece::King)
+ | chess::get_knight_moves(target_square) & blockers & board.pieces(Piece::Knight)
+ | chess::get_rook_moves(target_square, blockers)
+ & blockers
+ & (board.pieces(Piece::Rook) | board.pieces(Piece::Queen))
+ | chess::get_bishop_moves(target_square, blockers)
+ & blockers
+ & (board.pieces(Piece::Bishop) | board.pieces(Piece::Queen))
+ | chess::get_pawn_attacks(target_square, Color::Black, *white_pieces)
+ | chess::get_pawn_attacks(target_square, Color::White, *black_pieces);
+
+ let mut target_piece = board.piece_on(capture.get_source()).unwrap();
+ let mut colour = !initial_colour;
+ let mut gains = vec![piece_value(initial_capture)];
+
+ 'exchange: loop {
+ for attacker_piece in [
+ Piece::Pawn,
+ Piece::Knight,
+ Piece::Bishop,
+ Piece::Rook,
+ Piece::Queen,
+ Piece::King,
+ ] {
+ let our_attacker =
+ attackers & board.color_combined(colour) & board.pieces(attacker_piece);
+
+ if our_attacker == chess::EMPTY {
+ continue;
+ }
+
+ let attacker_square = our_attacker.to_square();
+ let victim_value = piece_value(target_piece);
+ gains.push(victim_value);
+
+ if target_piece == Piece::King {
+ break;
+ }
+
+ blockers ^= BitBoard::from_square(attacker_square);
+ attackers ^= BitBoard::from_square(attacker_square);
+
+ target_piece = attacker_piece;
+
+ if matches!(attacker_piece, Piece::Rook | Piece::Queen) {
+ attackers |= chess::get_rook_moves(target_square, blockers)
+ & blockers
+ & (board.pieces(Piece::Rook) | board.pieces(Piece::Queen));
+ }
+
+ if matches!(attacker_piece, Piece::Pawn | Piece::Bishop | Piece::Queen) {
+ attackers |= chess::get_bishop_moves(target_square, blockers)
+ & blockers
+ & (board.pieces(Piece::Bishop) | board.pieces(Piece::Queen));
+ }
+
+ colour = !colour;
+
+ continue 'exchange;
+ }
+
+ while gains.len() > 1 {
+ let forced = gains.len() == 2;
+
+ let their_gain = gains.pop().unwrap();
+ let our_gain = gains.last_mut().unwrap();
+
+ *our_gain -= their_gain;
+
+ if !forced && *our_gain < 0 {
+ *our_gain = 0;
+ }
+ }
+
+ return Value::new(gains.pop().unwrap());
+ }
+ }
}
/// Piece values for use with MVV/LVA only.
@@ -156,3 +247,57 @@ impl std::ops::DerefMut for MoveVec {
&mut self.0
}
}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ macro_rules! test_see {
+ ($name:ident, $fen:expr, $capture:expr, $expected:expr) => {
+ #[test]
+ fn $name() {
+ let board: Board = $fen.parse().unwrap();
+ let capture: ChessMove = $capture.parse().unwrap();
+ let expected = Value::new($expected);
+
+ assert_eq!(expected, MoveVec::see(&board, capture));
+ }
+ };
+ }
+
+ test_see!(
+ test_see_pawn_takes_protected_pawn,
+ "4R3/2r3p1/5bk1/1p1r3p/p2PR1P1/P1BK4/1P6/8 b - - 0 1",
+ "h5g4",
+ 0
+ );
+ test_see!(
+ test_see_two_pawn_takes_doubly_protocted_pawn,
+ "4R3/2r3p1/5bk1/1p1r1p1p/p2PR1P1/P1BK1P2/1P6/8 b - - 0 1",
+ "h5g4",
+ 0
+ );
+
+ //#[test]
+ //fn test_see_enough_attackers_but_wrong_order() {
+ // let board: Board = "k2r2q1/2n2b2/2p5/3n4/2K1P3/3QNB2/3R4/8 w - - 0 1"
+ // .parse()
+ // .unwrap();
+ // let capture: ChessMove = "e4d5".parse().unwrap();
+ //
+ // //assert_eq!(Value::INFINITE, MoveVec::see(&board, capture));
+ //
+ // for capture in MoveGen::new_legal(&board) {
+ // if capture.captures(&board).is_none() {
+ // continue;
+ // }
+ //
+ // println!(
+ // "{} SEE: {}",
+ // capture,
+ // MoveVec::see(&board, capture).as_inner()
+ // );
+ // }
+ // panic!();
+ //}
+}
diff --git a/engine/src/search/cuts.rs b/engine/src/search/cuts.rs
index 3f77610..8df0359 100644
--- a/engine/src/search/cuts.rs
+++ b/engine/src/search/cuts.rs
@@ -72,6 +72,7 @@ impl Searcher<'_> {
/// Early return with [`Value::DRAW`] if the position is a draw.
/// TODO: check for upcomming draw by repetition and increase alpha if alpha<draw
+ /// TODO: Check for draw by insufficient material
#[inline]
pub fn return_if_draw(&self, board: &Board, ply: Ply) -> Result<(), Value> {
if self.is_draw(board, ply) {