castling: simplify castle updates

src/castling.rs

@@ -1,19 +1,21 @@
 //! Castling flags.
 
-pub const CASTLING_WH_K: u8    = 0b00000001;
+pub type Castle = u8;
-pub const CASTLING_WH_Q: u8    = 0b00000010;
+
-pub const CASTLING_WH_MASK: u8 = 0b00000011;
+pub const CASTLING_WH_K: Castle    = 0b00000001;
-pub const CASTLING_BL_K: u8    = 0b00000100;
+pub const CASTLING_WH_Q: Castle    = 0b00000010;
-pub const CASTLING_BL_Q: u8    = 0b00001000;
+pub const CASTLING_WH_MASK: Castle = 0b00000011;
-pub const CASTLING_BL_MASK: u8 = 0b00001100;
+pub const CASTLING_BL_K: Castle    = 0b00000100;
-pub const CASTLING_K_MASK: u8  = 0b00000101;
+pub const CASTLING_BL_Q: Castle    = 0b00001000;
-pub const CASTLING_Q_MASK: u8  = 0b00001010;
+pub const CASTLING_BL_MASK: Castle = 0b00001100;
-pub const CASTLING_MASK: u8    = 0b00001111;
+pub const CASTLING_K_MASK: Castle  = 0b00000101;
+pub const CASTLING_Q_MASK: Castle  = 0b00001010;
+pub const CASTLING_MASK: Castle    = 0b00001111;
 
 /// Castling sides parameters.
 ///
 /// For both sides, the 3-uple contains files that should be empty
 /// and not attacked, an optional file that should be empty for
 /// queen-side, and the castling side-mask.
-pub const CASTLING_SIDES: [([i8; 2], Option<i8>, u8); 2] =
+pub const CASTLING_SIDES: [([i8; 2], Option<i8>, Castle); 2] =
     [([5i8, 6i8], None, CASTLING_K_MASK), ([3i8, 2i8], Some(1i8), CASTLING_Q_MASK)];

src/movement.rs

@@ -6,9 +6,6 @@ use crate::board::*;
 use crate::castling::*;
 use crate::rules::GameState;
 
-const START_WH_K_POS: Square = E1;
-const START_BL_K_POS: Square = E8;
-
 /// A movement, with before/after positions and optional promotion.
 #[derive(Clone, PartialEq)]
 pub struct Move {
@@ -39,119 +36,50 @@ impl Move {
 
     /// Apply this move to `board` and `game_state`.
     pub fn apply_to(&self, board: &mut Board, game_state: &mut GameState) {
-        // If a rook is taken, remove its castling option. Needs to be checked before we update
+        // If a king moves, remove it from castling options.
-        // board. Note that we only check for a piece going to rook's initial position: it means
+        if self.source == E1 { game_state.castling &= !CASTLING_WH_MASK; }
-        // the rook either moved previously, or it has been taken.
+        else if self.source == E8 { game_state.castling &= !CASTLING_BL_MASK; }
-        match self.source {
+        // Same for rooks.
-            A1 => { game_state.castling &= !CASTLING_WH_Q; }
+        if self.source == A1 || self.dest == A1 { game_state.castling &= !CASTLING_WH_Q; }
-            H1 => { game_state.castling &= !CASTLING_WH_K; }
+        else if self.source == H1 || self.dest == H1 { game_state.castling &= !CASTLING_WH_K; }
-            A8 => { game_state.castling &= !CASTLING_BL_Q; }
+        else if self.source == A8 || self.dest == A8 { game_state.castling &= !CASTLING_BL_Q; }
-            H8 => { game_state.castling &= !CASTLING_BL_K; }
+        else if self.source == H8 || self.dest == H8 { game_state.castling &= !CASTLING_BL_K; }
-            _ => {}
-        }
-
         // Update board and game state.
         self.apply_to_board(board);
         game_state.color = opposite(game_state.color);
-
-        // If the move is a castle, remove it from castling options.
-        if let Some(castle) = self.get_castle() {
-            match castle {
-                CASTLING_WH_K | CASTLING_WH_Q => game_state.castling &= !CASTLING_WH_MASK,
-                CASTLING_BL_K | CASTLING_BL_Q => game_state.castling &= !CASTLING_BL_MASK,
-                _ => {}
-            };
-        }
-        // Else, check if the king or a rook moved to update castling options.
-        else {
-            let color = board.get_color_on(self.dest);
-            if color == WHITE && game_state.castling & CASTLING_WH_MASK != 0 {
-                match board.get_piece_on(self.dest) {
-                    KING => {
-                        if self.source == E1 {
-                            game_state.castling &= !CASTLING_WH_MASK;
-                        }
-                    }
-                    ROOK => {
-                        if self.source == A1 {
-                            game_state.castling &= !CASTLING_WH_Q;
-                        } else if self.source == H1 {
-                            game_state.castling &= !CASTLING_WH_K;
-                        }
-                    }
-                    _ => {}
-                }
-            } else if color == BLACK && game_state.castling & CASTLING_BL_MASK != 0 {
-                match board.get_piece_on(self.dest) {
-                    KING => {
-                        if self.source == E8 {
-                            game_state.castling &= !CASTLING_BL_MASK;
-                        }
-                    }
-                    ROOK => {
-                        if self.source == A8 {
-                            game_state.castling &= !CASTLING_BL_Q;
-                        } else if self.source == H8 {
-                            game_state.castling &= !CASTLING_BL_K;
-                        }
-                    }
-                    _ => {}
-                }
-            }
-        }
     }
 
     /// Apply the move into `board`.
     pub fn apply_to_board(&self, board: &mut Board) {
+        let piece = board.get_piece_on(self.source);
+        // If a king is castling, apply special move.
+        if piece == KING {
             if let Some(castle) = self.get_castle() {
                 match castle {
-                CASTLING_WH_K => {
+                    CASTLING_WH_K => { board.move_square(E1, G1); board.move_square(H1, F1); }
-                    board.move_square(START_WH_K_POS, G1);
+                    CASTLING_WH_Q => { board.move_square(E1, C1); board.move_square(A1, D1); }
-                    board.move_square(H1, F1);
+                    CASTLING_BL_K => { board.move_square(E8, G8); board.move_square(H8, F8); }
+                    CASTLING_BL_Q => { board.move_square(E8, C8); board.move_square(A8, D8); }
+                    _ => { panic!("Invalid castle.") }
                 }
-                CASTLING_WH_Q => {
+                return
-                    board.move_square(START_WH_K_POS, C1);
-                    board.move_square(A1, D1);
             }
-                CASTLING_BL_K => {
-                    board.move_square(START_BL_K_POS, G8);
-                    board.move_square(H8, F8);
         }
-                CASTLING_BL_Q => {
-                    board.move_square(START_BL_K_POS, C8);
-                    board.move_square(A8, D8);
-                }
-                _ => {}
-            }
-        } else {
         board.move_square(self.source, self.dest);
         if let Some(piece) = self.promotion {
             let color = board.get_color_on(self.dest);
             board.set_square(self.dest, color, piece);
         }
     }
-    }
 
     /// Get the corresponding castling flag for this move.
-    pub fn get_castle(&self) -> Option<u8> {
+    pub fn get_castle(&self) -> Option<Castle> {
-        if self.source == E1 {
+        match (self.source, self.dest) {
-            if self.dest == C1 {
+            (E1, C1) => Some(CASTLING_WH_Q),
-                Some(CASTLING_WH_Q)
+            (E1, G1) => Some(CASTLING_WH_K),
-            } else if self.dest == G1 {
+            (E8, C8) => Some(CASTLING_BL_Q),
-                Some(CASTLING_WH_K)
+            (E8, G8) => Some(CASTLING_BL_K),
-            } else {
+            _ => None,
-                None
-            }
-        } else if self.source == E8 {
-            if self.dest == C8 {
-                Some(CASTLING_BL_Q)
-            } else if self.dest == G8 {
-                Some(CASTLING_BL_K)
-            } else {
-                None
-            }
-        } else {
-            None
         }
     }
 

src/node.rs

@@ -54,11 +54,6 @@ impl fmt::Display for Node {
         let mut s = vec!();
         self.board.draw(&mut s);
         let board_drawing = String::from_utf8_lossy(&s).to_string();
-        write!(
+        write!(f, "* Board:\n{}\nGame state: {}", board_drawing, self.game_state)
-            f,
-            "* Board:\n{}\n\
-             * Game state:\n{}",
-            board_drawing, self.game_state
-        )
     }
 }

src/rules.rs

@@ -43,11 +43,7 @@ impl std::fmt::Display for GameState {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         write!(
             f,
-            "- color: {}\n\
+            "[color: {}, castling: {:04b}, en_passant: {}, halfmove: {}, fullmove: {}]",
-             - castling: {:04b}\n\
-             - en_passant: {}\n\
-             - halfmove: {}\n\
-             - fullmove: {}",
             color_to_string(self.color), self.castling,
             fen::en_passant_to_string(self.en_passant),
             self.halfmove, self.fullmove