Add 'ChessBoard'

src/board/chess_board.rs

@@ -0,0 +1,187 @@
+use crate::error::Error;
+
+use super::{Bitboard, CastleRights, Color, File, FromFen, Move, Piece, Rank, Square};
+
+/// Represent an on-going chess game.
+#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub struct ChessBoard {
+    /// A [Bitboard] of occupancy for each piece type, discarding color. Indexed by [Piece::index].
+    piece_occupancy: [Bitboard; Piece::NUM_VARIANTS],
+    /// A [Bitboard] of occupancy for each color, discarding piece type. Indexed by [Piece::index].
+    color_occupancy: [Bitboard; Color::NUM_VARIANTS],
+    /// A [Bitboard] representing all squares currently occupied by a piece.
+    combined_occupancy: Bitboard,
+    /// The allowed [CastleRights] for either color. Indexed by [Color::index].
+    castle_rights: [CastleRights; Color::NUM_VARIANTS],
+    /// A potential en-passant attack.
+    /// Either `None` if no 2-square pawn move was made in the previous half-turn, or
+    /// `Some(target_square)` if a 2-square move was made.
+    en_passant: Option<Square>,
+    /// The number of half-turns without either a pawn push or capture.
+    half_move_clock: u8, // Should never go higher than 50.
+    /// The number of half-turns so far.
+    total_plies: u32, // Should be plenty.
+    /// The current player turn.
+    side: Color,
+}
+
+pub struct NonReversibleState {
+    castle_rights: [CastleRights; Color::NUM_VARIANTS],
+    en_passant: Option<Square>,
+    half_move_clock: u8, // Should never go higher than 50.
+}
+
+impl ChessBoard {
+    /// Which player's turn is it.
+    #[inline(always)]
+    pub fn current_player(&self) -> Color {
+        self.side
+    }
+
+    /// Return the [Square] currently occupied by a pawn that can be captured en-passant, or `None`
+    #[inline(always)]
+    pub fn en_passant(&self) -> Option<Square> {
+        self.en_passant
+    }
+
+    /// Return the [CastleRights] for the given [Color].
+    #[inline(always)]
+    pub fn castle_rights(&self, color: Color) -> CastleRights {
+        // SAFETY: we know the value is in-bounds
+        unsafe { *self.castle_rights.get_unchecked(color.index()) }
+    }
+
+    /// Return the [CastleRights] for the given [Color]. Allow mutations.
+    #[inline(always)]
+    fn castle_rights_mut(&mut self, color: Color) -> &mut CastleRights {
+        // SAFETY: we know the value is in-bounds
+        unsafe { &mut *self.castle_rights.get_unchecked_mut(color.index()) }
+    }
+
+    /// Get the [Bitboard] representing all pieces of the given [Piece] type, discarding color.
+    #[inline(always)]
+    pub fn piece_occupancy(&self, piece: Piece) -> Bitboard {
+        // SAFETY: we know the value is in-bounds
+        unsafe { *self.piece_occupancy.get_unchecked(piece.index()) }
+    }
+
+    /// Get the [Bitboard] representing all pieces of the given [Piece] type, discarding color.
+    /// Allow mutating the state.
+    #[inline(always)]
+    fn piece_occupancy_mut(&mut self, piece: Piece) -> &mut Bitboard {
+        // SAFETY: we know the value is in-bounds
+        unsafe { &mut *self.piece_occupancy.get_unchecked_mut(piece.index()) }
+    }
+
+    /// Get the [Bitboard] representing all colors of the given [Color] type, discarding piece
+    /// type.
+    #[inline(always)]
+    pub fn color_occupancy(&self, color: Color) -> Bitboard {
+        // SAFETY: we know the value is in-bounds
+        unsafe { *self.color_occupancy.get_unchecked(color.index()) }
+    }
+
+    /// Get the [Bitboard] representing all colors of the given [Color] type, discarding piece
+    /// type. Allow mutating the state.
+    #[inline(always)]
+    fn color_occupancy_mut(&mut self, color: Color) -> &mut Bitboard {
+        // SAFETY: we know the value is in-bounds
+        unsafe { &mut *self.color_occupancy.get_unchecked_mut(color.index()) }
+    }
+
+    /// Get the [Bitboard] representing all pieces on the board.
+    #[inline(always)]
+    pub fn combined_occupancy(&self) -> Bitboard {
+        self.combined_occupancy
+    }
+
+    /// Return the number of half-turns without either a pawn push or a capture.
+    #[inline(always)]
+    pub fn half_move_clock(&self) -> u8 {
+        self.half_move_clock
+    }
+
+    /// Return the total number of plies (i.e: half-turns) played so far.
+    #[inline(always)]
+    pub fn total_plies(&self) -> u32 {
+        self.total_plies
+    }
+
+    /// Quickly do and undo a move on the [Bitboard]s that are part of the [ChessBoard] state. Does
+    /// not account for all non-revertible changes such as en-passant state or half-move clock.
+    #[inline(always)]
+    fn xor(&mut self, color: Color, piece: Piece, start_end: Bitboard) {
+        *self.piece_occupancy_mut(piece) ^= start_end;
+        *self.color_occupancy_mut(color) ^= start_end;
+        self.combined_occupancy ^= start_end;
+    }
+
+    /// Play the given [Move], returning all non-revertible state (e.g: en-passant, etc...).
+    #[inline(always)]
+    pub fn do_move(&mut self, chess_move: Move) -> NonReversibleState {
+        // Save non-revertible state
+        let state = NonReversibleState {
+            castle_rights: self.castle_rights,
+            en_passant: self.en_passant,
+            half_move_clock: self.half_move_clock,
+        };
+
+        // Non-revertible state modification
+        if chess_move.capture().is_some() || chess_move.piece() == Piece::Pawn {
+            self.half_move_clock = 0;
+        } else {
+            self.half_move_clock += 1;
+        }
+        if chess_move.is_double_step() {
+            let target_square = Square::new(
+                chess_move.destination().file(),
+                self.current_player().third_rank(),
+            );
+            self.en_passant = Some(target_square);
+        } else {
+            self.en_passant = None;
+        }
+        if chess_move.is_castling() || chess_move.piece() == Piece::King {
+            *self.castle_rights_mut(self.current_player()) = CastleRights::NoSide;
+        }
+        if chess_move.piece() == Piece::Rook {
+            let castle_rights = self.castle_rights_mut(self.current_player());
+            *castle_rights = match chess_move.start().file() {
+                File::A => castle_rights.without_queen_side(),
+                File::H => castle_rights.without_king_side(),
+                _ => *castle_rights,
+            }
+        }
+
+        // Revertible state modification
+        self.xor(
+            self.current_player(),
+            chess_move.piece(),
+            chess_move.start() | chess_move.destination(),
+        );
+        self.total_plies += 1;
+        self.side = !self.side;
+
+        state
+    }
+
+    /// Reverse the effect of playing the given [Move], and return to the given
+    /// [NonReversibleState].
+    #[inline(always)]
+    pub fn undo_move(&mut self, chess_move: Move, state: NonReversibleState) {
+        // Restore non-revertible state
+        self.castle_rights = state.castle_rights;
+        self.en_passant = state.en_passant;
+        self.half_move_clock = state.half_move_clock;
+
+        // Restore revertible state
+        self.xor(
+            // The move was applied at the turn *before* the current player
+            !self.current_player(),
+            chess_move.piece(),
+            chess_move.start() | chess_move.destination(),
+        );
+        self.total_plies -= 1;
+        self.side = !self.side;
+    }
+}

src/board/mod.rs

@@ -4,6 +4,9 @@ pub use bitboard::*;
 pub mod castle_rights;
 pub use castle_rights::*;
 
+pub mod chess_board;
+pub use chess_board::*;
+
 pub mod color;
 pub use color::*;