Initial implementation of CheckingPieces and Position::checking_pieces()

position/src/check.rs

@@ -0,0 +1,29 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use chessfriend_bitboard::BitBoard;
+
+pub struct CheckingPieces {
+    pawn: BitBoard,
+    knight: BitBoard,
+    bishop: BitBoard,
+    rook: BitBoard,
+    queen: BitBoard,
+}
+
+impl CheckingPieces {
+    pub(crate) fn new(
+        pawn: BitBoard,
+        knight: BitBoard,
+        bishop: BitBoard,
+        rook: BitBoard,
+        queen: BitBoard,
+    ) -> CheckingPieces {
+        CheckingPieces {
+            pawn,
+            knight,
+            bishop,
+            rook,
+            queen,
+        }
+    }
+}

position/src/lib.rs

@@ -2,6 +2,7 @@
 
 pub mod fen;
 
+mod check;
 mod display;
 mod r#move;
 mod move_generator;

position/src/position/position.rs

@@ -249,6 +249,44 @@ impl Position {
             .next()
             .unwrap()
     }
+
+    pub(crate) fn checking_pieces(&self) -> CheckingPieces {
+        let opponent = self.color_to_move.other();
+        let king_square = self.king_square(self.color_to_move);
+
+        let checking_pawns = {
+            // The current player's pawn attack moves *from* this square are the
+            // same as the pawn moves for the opposing player attacking this square.
+            let pawn_moves_to_king_square = BitBoard::pawn_attacks(king_square, self.color_to_move);
+            let opposing_pawn = Piece::pawn(opponent);
+            let opposing_pawns = self.pieces.bitboard_for_piece(&opposing_pawn);
+
+            pawn_moves_to_king_square & opposing_pawns
+        };
+
+        macro_rules! checking_piece {
+            ($moves_bb_fn:path, $piece_fn:path) => {{
+                let moves_from_opposing_square = $moves_bb_fn(king_square);
+                let piece = $piece_fn(opponent);
+                let opposing_pieces = self.pieces.bitboard_for_piece(&piece);
+
+                moves_from_opposing_square & opposing_pieces
+            }};
+        }
+
+        let checking_knights = checking_piece!(BitBoard::knight_moves, Piece::knight);
+        let checking_bishops = checking_piece!(BitBoard::bishop_moves, Piece::bishop);
+        let checking_rooks = checking_piece!(BitBoard::rook_moves, Piece::rook);
+        let checking_queens = checking_piece!(BitBoard::queen_moves, Piece::queen);
+
+        CheckingPieces::new(
+            checking_pawns,
+            checking_knights,
+            checking_bishops,
+            checking_rooks,
+            checking_queens,
+        )
+    }
 }
 
 // crate::position methods