engine: basic Shannon board evaluation and stats

src/board.rs

@@ -8,6 +8,7 @@ pub const SQ_N: u8 = 0b00000100;
 pub const SQ_R: u8         = 0b00001000;
 pub const SQ_Q: u8         = 0b00010000;
 pub const SQ_K: u8         = 0b00100000;
+pub const SQ_TYPE_MASK: u8 = 0b00111111;
 
 // Piece color flags.
 pub const SQ_WH: u8         = 0b01000000;
@@ -32,18 +33,28 @@ pub const SQ_BL_K: u8 = SQ_BL|SQ_K;
 pub fn has_flag(i: u8, flag: u8) -> bool { i & flag == flag }
 
 // Wrappers for clearer naming.
+/// Get type of piece on square, without color.
+#[inline]
+pub fn get_type(square: u8) -> u8 { square & SQ_TYPE_MASK }
+/// Return true if the piece on this square is of type `piece_type`.
+#[inline]
+pub fn is_type(square: u8, piece_type: u8) -> bool { get_type(square) == piece_type }
+/// Return true if the piece on this square is the same as `piece`.
 #[inline]
 pub fn is_piece(square: u8, piece: u8) -> bool { has_flag(square, piece) }
+/// Return true if the piece on this square has this color.
 #[inline]
 pub fn is_color(square: u8, color: u8) -> bool { has_flag(square, color) }
+/// Return true if this square has a white piece.
 #[inline]
 pub fn is_white(square: u8) -> bool { is_color(square, SQ_WH) }
+/// Return true if this square has a black piece.
 #[inline]
 pub fn is_black(square: u8) -> bool { is_color(square, SQ_BL) }
-
+/// Return the color of the piece on this square.
-/// Get piece color.
 #[inline]
 pub fn get_color(square: u8) -> u8 { square & SQ_COLOR_MASK }
+
 /// Get opposite color.
 #[inline]
 pub fn opposite(color: u8) -> u8 { color ^ SQ_COLOR_MASK }
@@ -155,7 +166,15 @@ pub fn is_empty(board: &Board, coords: &Pos) -> bool {
     get_square(board, coords) == SQ_E
 }
 
-/// Count number of pieces on board
+pub fn get_piece_iterator<'a>(board: &'a Board) -> Box<dyn Iterator<Item = (u8, Pos)> + 'a> {
+    Box::new(
+        board.iter().enumerate()
+            .filter(|(_, s)| **s != SQ_E)
+            .map(|(i, s)| (*s, ((i / 8) as i8, (i % 8) as i8)))
+    )
+}
+
+/// Count number of pieces on board. Used for debugging.
 pub fn num_pieces(board: &Board) -> u8 {
     let mut count = 0;
     for i in board.iter() {
@@ -180,22 +199,7 @@ pub fn find_king(board: &Board, color: u8) -> Pos {
     (0, 0)
 }
 
-/// A movement, with before/after positions and optional promotion.
+/// Write a text view of the board. Used for debugging.
-pub type Move = (Pos, Pos, Option<u8>);
-
-/// Apply a move `m` to a copy of `board`.
-pub fn apply(board: &Board, m: &Move) -> Board {
-    let mut new_board = board.clone();
-    apply_into(&mut new_board, m);
-    new_board
-}
-
-/// Apply a move `m` into `board`.
-pub fn apply_into(board: &mut Board, m: &Move) {
-    set_square(board, &m.1, get_square(board, &m.0));
-    clear_square(board, &m.0)
-}
-
 pub fn draw(board: &Board, f: &mut dyn std::io::Write) {
     for r in (0..8).rev() {
         let mut rank = String::with_capacity(8);
@@ -217,6 +221,160 @@ pub fn draw(board: &Board, f: &mut dyn std::io::Write) {
     writeln!(f, "  abcdefgh").unwrap();
 }
 
+/// A movement, with before/after positions and optional promotion.
+pub type Move = (Pos, Pos, Option<u8>);
+
+/// Apply a move `m` to a copy of `board`.
+pub fn apply(board: &Board, m: &Move) -> Board {
+    let mut new_board = board.clone();
+    apply_into(&mut new_board, m);
+    new_board
+}
+
+/// Apply a move `m` into `board`.
+pub fn apply_into(board: &mut Board, m: &Move) {
+    set_square(board, &m.1, get_square(board, &m.0));
+    clear_square(board, &m.0)
+}
+
+/// Storage for precomputed board pieces stats.
+#[derive(Debug, Clone, PartialEq)]
+pub struct BoardStats {
+    pub num_pawns: i8,
+    pub num_bishops: i8,
+    pub num_knights: i8,
+    pub num_rooks: i8,
+    pub num_queens: i8,
+    pub num_kings: i8,
+    pub num_doubled_pawns: i8,   // Pawns that are on the same file as a friend.
+    pub num_backward_pawns: i8,  // Pawns behind all other pawns on adjacent files.
+    pub num_isolated_pawns: i8,  // Pawns that have no friend pawns on adjacent files.
+    pub mobility: i32,
+}
+
+impl BoardStats {
+    pub fn new() -> BoardStats {
+        BoardStats {
+            num_pawns: 0, num_bishops: 0, num_knights: 0, num_rooks: 0, num_queens: 0,
+            num_kings: 0, num_doubled_pawns: 0, num_backward_pawns: 0, num_isolated_pawns: 0,
+            mobility: 0,
+        }
+    }
+
+    pub fn reset(&mut self) {
+        self.num_pawns = 0;
+        self.num_bishops = 0;
+        self.num_knights = 0;
+        self.num_rooks = 0;
+        self.num_queens = 0;
+        self.num_kings = 0;
+        self.num_doubled_pawns = 0;
+        self.num_backward_pawns = 0;
+        self.num_isolated_pawns = 0;
+        self.mobility = 0;
+    }
+}
+
+/// Create two new BoardStats objects from the board, for white and black.
+///
+/// See `compute_stats_into` for details.
+pub fn compute_stats(board: &Board) -> (BoardStats, BoardStats) {
+    let mut stats = (BoardStats::new(), BoardStats::new());
+    compute_stats_into(board, &mut stats);
+    stats
+}
+
+pub fn compute_stats_into(board: &Board, stats: &mut (BoardStats, BoardStats)) {
+    compute_color_stats_into(board, &mut stats.0, SQ_WH);
+    compute_color_stats_into(board, &mut stats.1, SQ_BL);
+}
+
+/// Update `stats` for `color` from given `board`
+///
+/// Refresh all stats *except* `mobility`.
+pub fn compute_color_stats_into(board: &Board, stats: &mut BoardStats, color: u8) {
+    stats.reset();
+    for (piece, (pos_f, pos_r)) in get_piece_iterator(board) {
+        if piece == SQ_E || !is_color(piece, color) {
+            continue
+        }
+        match get_type(piece) {
+            SQ_P => {
+                stats.num_pawns += 1;
+                let mut doubled = false;
+                let mut isolated = true;
+                let mut backward = true;
+                for r in 0..8 {
+                    // Check for doubled pawns.
+                    if
+                        !doubled &&
+                        is_piece(get_square(board, &(pos_f, r)), color|SQ_P) && r != pos_r
+                    {
+                        doubled = true;
+                    }
+                    // Check for isolated pawns.
+                    if
+                        isolated &&
+                        (
+                            // Check on the left file if not on a-file...
+                            (
+                                pos_f > POS_MIN &&
+                                is_piece(get_square(board, &(pos_f - 1, r)), color|SQ_P)
+                            ) ||
+                            // Check on the right file if not on h-file...
+                            (
+                                pos_f < POS_MAX &&
+                                is_piece(get_square(board, &(pos_f + 1, r)), color|SQ_P)
+                            )
+                        )
+                    {
+                        isolated = false;
+                    }
+                    // Check for backward pawns.
+                    if backward {
+                        if color == SQ_WH && r <= pos_r {
+                            if (
+                                pos_f > POS_MIN &&
+                                is_type(get_square(board, &(pos_f - 1, r)), SQ_P)
+                            ) || (
+                                pos_f < POS_MAX &&
+                                is_type(get_square(board, &(pos_f + 1, r)), SQ_P)
+                            ) {
+                                backward = false;
+                            }
+                        } else if color == SQ_BL && r >= pos_r {
+                            if (
+                                pos_f > POS_MIN &&
+                                is_type(get_square(board, &(pos_f - 1, r)), SQ_P)
+                            ) || (
+                                pos_f < POS_MAX &&
+                                is_type(get_square(board, &(pos_f + 1, r)), SQ_P)
+                            ) {
+                                backward = false;
+                            }
+                        }
+                    }
+                }
+                if doubled {
+                    stats.num_doubled_pawns += 1;
+                }
+                if isolated {
+                    stats.num_isolated_pawns += 1;
+                }
+                if backward {
+                    stats.num_backward_pawns += 1;
+                }
+            },
+            SQ_R => stats.num_rooks += 1,
+            SQ_N => stats.num_knights += 1,
+            SQ_B => stats.num_bishops += 1,
+            SQ_Q => stats.num_queens += 1,
+            SQ_K => stats.num_kings += 1,
+            _ => {}
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -316,4 +474,73 @@ mod tests {
         assert_eq!(get_square(&b, &pos("e6")), SQ_BL_N);
         assert_eq!(num_pieces(&b), 1);
     }
+
+    #[test]
+    fn test_compute_stats() {
+        // Check that initial stats are correct.
+        let b = new();
+        let initial_stats = BoardStats {
+            num_pawns: 8,
+            num_bishops: 2,
+            num_knights: 2,
+            num_rooks: 2,
+            num_queens: 1,
+            num_kings: 1,
+            num_doubled_pawns: 0,
+            num_backward_pawns: 0,
+            num_isolated_pawns: 0,
+            mobility: 0,
+        };
+        let mut stats = compute_stats(&b);
+        assert!(stats.0 == stats.1);
+        assert!(stats.0 == initial_stats);
+
+        // Check that doubled pawns are correctly counted.
+        let mut b = new_empty();
+        set_square(&mut b, &pos("d4"), SQ_WH_P);
+        set_square(&mut b, &pos("d6"), SQ_WH_P);
+        compute_color_stats_into(&b, &mut stats.0, SQ_WH);
+        assert_eq!(stats.0.num_doubled_pawns, 2);
+        // Add a pawn on another file, no changes expected.
+        set_square(&mut b, &pos("e6"), SQ_WH_P);
+        compute_color_stats_into(&b, &mut stats.0, SQ_WH);
+        assert_eq!(stats.0.num_doubled_pawns, 2);
+        // Add a pawn backward in the d-file: there are now 3 doubled pawns.
+        set_square(&mut b, &pos("d2"), SQ_WH_P);
+        compute_color_stats_into(&b, &mut stats.0, SQ_WH);
+        assert_eq!(stats.0.num_doubled_pawns, 3);
+
+        // Check that isolated and backward pawns are correctly counted.
+        assert_eq!(stats.0.num_isolated_pawns, 0);
+        assert_eq!(stats.0.num_backward_pawns, 2);  // A bit weird?
+        // Protect d4 pawn with a friend in e3: it is not isolated nor backward anymore.
+        set_square(&mut b, &pos("e3"), SQ_WH_P);
+        compute_color_stats_into(&b, &mut stats.0, SQ_WH);
+        assert_eq!(stats.0.num_doubled_pawns, 5);
+        assert_eq!(stats.0.num_isolated_pawns, 0);
+        assert_eq!(stats.0.num_backward_pawns, 1);
+        // Add an adjacent friend to d2 pawn: no pawns are left isolated or backward.
+        set_square(&mut b, &pos("c2"), SQ_WH_P);
+        compute_color_stats_into(&b, &mut stats.0, SQ_WH);
+        assert_eq!(stats.0.num_doubled_pawns, 5);
+        assert_eq!(stats.0.num_isolated_pawns, 0);
+        assert_eq!(stats.0.num_backward_pawns, 0);
+        // Add an isolated/backward white pawn in a far file.
+        set_square(&mut b, &pos("a2"), SQ_WH_P);
+        compute_color_stats_into(&b, &mut stats.0, SQ_WH);
+        assert_eq!(stats.0.num_doubled_pawns, 5);
+        assert_eq!(stats.0.num_isolated_pawns, 1);
+        assert_eq!(stats.0.num_backward_pawns, 1);
+
+        // Check for pawns that are backward but not isolated.
+        let mut b = new_empty();
+        // Here, d4 pawn protects both e5 and e3, but it is backward.
+        set_square(&mut b, &pos("d4"), SQ_WH_P);
+        set_square(&mut b, &pos("e5"), SQ_WH_P);
+        set_square(&mut b, &pos("e3"), SQ_WH_P);
+        compute_color_stats_into(&b, &mut stats.0, SQ_WH);
+        assert_eq!(stats.0.num_doubled_pawns, 2);
+        assert_eq!(stats.0.num_isolated_pawns, 0);
+        assert_eq!(stats.0.num_backward_pawns, 1);
+    }
 }

src/engine.rs

@@ -13,6 +13,8 @@ use crate::uci;
 
 /// Analysis engine.
 pub struct Engine {
+    /// Debug mode, log some data.
+    debug: bool,
     /// Current game state, starting point of further analysis.
     state: GameState,
     /// Communication mode.
@@ -30,6 +32,7 @@ pub struct Engine {
 #[derive(Clone)]
 struct GameState {
     board: board::Board,
+    stats: (board::BoardStats, board::BoardStats),  // white and black pieces stats.
     color: u8,
     castling: u8,
     en_passant: Option<board::Pos>,
@@ -37,6 +40,17 @@ struct GameState {
     fullmove: i32,
 }
 
+impl std::fmt::Debug for GameState {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(
+            f,
+            "GameState {{ board: [...], stats: {:?}, color: {:08b}, castling: {:08b}, \
+             en_passant: {:?}, halfmove: {}, fullmove: {} }}",
+            self.stats, self.color, self.castling, self.en_passant, self.halfmove, self.fullmove
+        )
+    }
+}
+
 /// Engine communication mode.
 enum Mode {
     /// No mode, sit here and do nothing.
@@ -59,11 +73,21 @@ pub enum Cmd {
     UciGo(Vec<uci::GoArgs>),              // UCI "go" command.
     Stop,                                 // Stop working ASAP.
     TmpBestMove(Option<board::Move>),  // Send best move found by analysis worker (TEMPORARY).
+    WorkerInfo(Vec<Info>),                // Informations from a worker.
 
     // Commands that can be sent by the engine.
+    /// Ask for a string to be logged or printed.
+    ///
+    /// Note that workers can send this command to engine, expecting
+    /// the message to be forwarded to whatever can log.
+    Log(String),
+    /// Report found best move.
     BestMove(Option<board::Move>),
+    /// Report ongoing analysis information.
+    Info(Vec<Info>),
 }
 
+/// Parameters for starting work.
 #[derive(Clone)]
 struct WorkArgs {
     move_time: i32,
@@ -73,6 +97,12 @@ struct WorkArgs {
     black_inc: i32,
 }
 
+/// Information to be transmitted back to whatever is listening.
+#[derive(Debug, Clone)]
+pub enum Info {
+    CurrentMove(board::Move),
+}
+
 pub const CASTLING_WH_K: u8 = 0b00000001;
 pub const CASTLING_WH_Q: u8 = 0b00000010;
 pub const CASTLING_BL_K: u8 = 0b00000100;
@@ -83,8 +113,10 @@ pub const CASTLING_MASK: u8 = 0b00001111;
 impl Engine {
     pub fn new() -> Engine {
         Engine {
+            debug: true,
             state: GameState {
                 board: board::new_empty(),
+                stats: (board::BoardStats::new(), board::BoardStats::new()),
                 color: board::SQ_WH,
                 castling: CASTLING_MASK,
                 en_passant: None,
@@ -124,6 +156,8 @@ impl Engine {
             Cmd::UciGo(args) => self.uci_go(&args),
             Cmd::Stop => self.stop(),
             // Workers commands.
+            Cmd::Log(s) => self.reply(Cmd::Log(s.to_string())),
+            Cmd::WorkerInfo(infos) => self.reply(Cmd::Info(infos.to_vec())),
             Cmd::TmpBestMove(m) => self.reply(Cmd::BestMove(*m)),
             _ => eprintln!("Not an engine input command: {:?}", cmd),
         }
@@ -142,7 +176,6 @@ impl Engine {
     ///
     /// For speed purposes, it assumes values are always valid.
     fn apply_fen(&mut self, fen: &notation::Fen) {
-        eprintln!("Applying FEN {:?}", fen);
         self.set_fen_placement(&fen.placement);
         self.set_fen_color(&fen.color);
         self.set_fen_castling(&fen.castling);
@@ -202,13 +235,18 @@ impl Engine {
     ///
     /// Stop working after `movetime` ms, or go on forever if it's -1.
     fn work(&mut self, args: &WorkArgs) {
+        if self.debug {
+            self.reply(Cmd::Log(format!("Current evaluation: {}", evaluate(&self.state.stats))));
+        }
+
         self.working.store(true, atomic::Ordering::Relaxed);
         let state = self.state.clone();
         let args = args.clone();
         let working = self.working.clone();
         let tx = match &self.mode { Mode::Uci(_, _, tx) => tx.clone(), _ => return };
+        let debug = self.debug;
         thread::spawn(move || {
-            analyze(&state, &args, working, tx);
+            analyze(&state, &args, working, tx, debug);
         });
     }
 
@@ -249,6 +287,7 @@ impl Engine {
                 }
             }
         }
+        board::compute_stats_into(&self.state.board, &mut self.state.stats);
     }
 
     /// Start working using parameters passed with a "go" command.
@@ -280,6 +319,7 @@ fn analyze(
     _args: &WorkArgs,
     wip: Arc<atomic::AtomicBool>,
     tx: mpsc::Sender<Cmd>,
+    debug: bool,
 ) {
     if !wip.load(atomic::Ordering::Relaxed) {
         return;
@@ -287,9 +327,38 @@ fn analyze(
 
     // Stupid engine! Return a random move.
     let moves = rules::get_player_legal_moves(&state.board, state.color);
-    let mut rng = rand::thread_rng();
+    if debug {
-    let best_move = moves.iter().choose(&mut rng).and_then(|m| Some(*m));
+        let state_str = format!("Current state: {:?}", state);
-    thread::sleep(time::Duration::from_millis(300u64));
+        tx.send(Cmd::Log(state_str)).unwrap();
+        let mut s = vec!();
+        board::draw(&state.board, &mut s);
+        let draw_str = String::from_utf8_lossy(&s).to_string();
+        tx.send(Cmd::Log(draw_str)).unwrap();
+        let moves_str = format!("Legal moves: {}", notation::move_list_to_string(&moves));
+        tx.send(Cmd::Log(moves_str)).unwrap();
+    }
+    // let mut rng = rand::thread_rng();
+    // let best_move = moves.iter().choose(&mut rng).and_then(|m| Some(*m));
+
+    let mut best_e = if board::is_white(state.color) { -999.0 } else { 999.0 };
+    let mut best_move = None;
+    for m in moves {
+        // tx.send(Cmd::WorkerInfo(vec!(Info::CurrentMove(m)))).unwrap();
+        let mut board = state.board.clone();
+        board::apply_into(&mut board, &m);
+        let stats = board::compute_stats(&board);
+        let e = evaluate(&stats);
+        tx.send(Cmd::Log(format!("Move {} eval {}", notation::move_to_string(&m), e))).unwrap();
+
+        if
+            (board::is_white(state.color) && e > best_e) ||
+            (board::is_black(state.color) && e < best_e)
+        {
+            best_e = e;
+            best_move = Some(m.clone());
+        }
+    }
+    thread::sleep(time::Duration::from_millis(500u64));
     tx.send(Cmd::TmpBestMove(best_move)).unwrap();
 
     // thread::sleep(time::Duration::from_secs(1));
@@ -302,3 +371,37 @@ fn analyze(
     // }
 
 }
+
+fn evaluate(stats: &(board::BoardStats, board::BoardStats)) -> f32 {
+    let (ws, bs) = stats;
+    (
+        200.0 * (ws.num_kings - bs.num_kings) as f32
+        + 9.0 * (ws.num_queens - bs.num_queens) as f32
+        + 5.0 * (ws.num_rooks - bs.num_rooks) as f32
+        + 3.0 * (ws.num_bishops - bs.num_bishops) as f32
+        + 3.0 * (ws.num_knights - bs.num_knights) as f32
+        + (ws.num_pawns - bs.num_pawns) as f32
+        + 0.5 * (  // FIXME
+            ws.num_doubled_pawns - bs.num_doubled_pawns +
+            ws.num_isolated_pawns - bs.num_isolated_pawns +
+            ws.num_backward_pawns - bs.num_backward_pawns
+        ) as f32
+        + 0.1 * (ws.mobility - bs.mobility) as f32
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_evaluate() {
+        let mut b = board::new();
+        let stats = board::compute_stats(&b);
+        assert_eq!(evaluate(&stats), 0.0);
+
+        board::apply_into(&mut b, &(notation::parse_move("d2d4")));
+        let stats = board::compute_stats(&b);
+        assert_eq!(evaluate(&stats), 0.0);
+    }
+}

src/notation.rs

@@ -4,6 +4,7 @@ use crate::board;
 
 pub const NULL_MOVE: &str = "0000";
 
+/// Create a string containing the UCI algebraic notation of this move.
 pub fn move_to_string(m: &board::Move) -> String {
     let mut move_string = String::new();
     move_string.push_str(&board::pos_string(&m.0));
@@ -20,6 +21,7 @@ pub fn move_to_string(m: &board::Move) -> String {
     move_string
 }
 
+/// Parse an UCI move algebraic notation string to a board::Move.
 pub fn parse_move(m_str: &str) -> board::Move {
     let prom = if m_str.len() == 5 {
         Some(match m_str.as_bytes()[4] {
@@ -35,6 +37,11 @@ pub fn parse_move(m_str: &str) -> board::Move {
     (board::pos(&m_str[0..2]), board::pos(&m_str[2..4]), prom)
 }
 
+/// Create a space-separated string of moves. Used for debugging.
+pub fn move_list_to_string(moves: &Vec<board::Move>) -> String {
+    moves.iter().map(|m| move_to_string(m)).collect::<Vec<_>>().join(" ")
+}
+
 pub const FEN_START: &str = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
 
 /// FEN notation for positions, split into fields.

src/uci.rs

@@ -195,11 +195,17 @@ impl Uci {
 
     /// Handle an engine command.
     fn handle_engine_command(&mut self, cmd: &engine::Cmd) {
-        self.log(format!("ENG >>> {:?}", cmd));
         match cmd {
             engine::Cmd::UciChannel(s) => {
+                self.log("ENG >>> Channel opened.".to_string());
                 self.engine_in = Some(s.to_owned());
             }
+            engine::Cmd::Log(s) => {
+                self.log(s.to_string());
+            }
+            engine::Cmd::Info(infos) => {
+                self.send_infos(infos);
+            }
             engine::Cmd::BestMove(m) => {
                 self.state = State::Ready;
                 self.send_bestmove(m);
@@ -229,6 +235,19 @@ impl Uci {
         self.send("readyok");
     }
 
+    /// Send engine analysis information.
+    fn send_infos(&mut self, infos: &Vec<engine::Info>) {
+        let mut s = "info".to_string();
+        for i in infos {
+            match i {
+                engine::Info::CurrentMove(m) => {
+                    s.push_str(&format!(" currmove {}", notation::move_to_string(m)));
+                }
+            }
+        }
+        self.send(&s);
+    }
+
     /// Send best move.
     fn send_bestmove(&mut self, m: &Option<board::Move>) {
         let move_str = match m {