add custom chess engine

2026-06-08 13:58:22 -06:00
parent d2ae34f530
commit c3280aa6d3
42 changed files with 3033 additions and 168 deletions
@@ -0,0 +1,87 @@
+// The board. Hybrid representation: bitboards (per piece type and per color)
+// for fast generation/attacks, plus a piece-on-square mailbox for O(1)
+// "what's here?" queries. do_move/undo_move keep both in sync, along with the
+// Zobrist key. One Position is one game line; it is freely copyable.
+#ifndef CHESS_POSITION_H
+#define CHESS_POSITION_H
+
+#include "types.h"
+#include "bitboard.h"
+
+#include <string>
+#include <string_view>
+
+namespace chess {
+
+class Position {
+public:
+    /// Parse a FEN string into a position.
+    static Position from_fen(std::string_view fen);
+    /// Serialize back to FEN.
+    std::string to_fen() const;
+
+    // --- mailbox queries ---
+    Piece  piece_on(Square s)  const { return board[s]; }
+    bool   empty(Square s)     const { return board[s] == NO_PIECE; }
+    Color  side_to_move()      const { return sideToMove; }
+    Square ep_square()         const { return epSquare; }
+    int    halfmove_clock()    const { return rule50; }
+    int    fullmove_number()   const { return 1 + gamePly / 2; }
+    bool   can_castle(Color c, CastlingSide side) const;
+    Square king_square(Color c) const { return lsb(pieces(c, KING)); }
+
+    // --- bitboard accessors ---
+    Bitboard pieces()                      const { return byColorBB[WHITE] | byColorBB[BLACK]; }
+    Bitboard pieces(Color c)               const { return byColorBB[c]; }
+    Bitboard pieces(PieceType pt)          const { return byTypeBB[pt]; }
+    Bitboard pieces(Color c, PieceType pt) const { return byTypeBB[pt] & byColorBB[c]; }
+
+    // --- attacks / checks ---
+    Bitboard attackers_to(Square s) const { return attackers_to(s, pieces()); }
+    Bitboard attackers_to(Square s, Bitboard occ) const;
+    bool     in_check() const;                 // is side_to_move in check?
+    bool     gives_check(Move m);              // does m check the opponent?
+
+    // --- the three you asked for ---
+    void generate_legal(MoveList& list);       // defined in movegen.cpp
+    void do_move(Move m);
+    void undo_move(Move m);
+
+    // --- freebies ---
+    uint64_t key()     const { return zkey; }
+    bool     is_draw() const;                  // 50-move + threefold + insufficient material
+    void     print()   const;
+
+private:
+    void put_piece(Piece pc, Square s);
+    void remove_piece(Square s);
+    void move_piece(Square from, Square to);
+    bool insufficient_material() const;
+
+    Bitboard byTypeBB[PIECE_TYPE_NB];
+    Bitboard byColorBB[COLOR_NB];
+    Piece    board[SQUARE_NB];
+    Color    sideToMove;
+    int      castlingRights;
+    Square   epSquare;
+    int      rule50;
+    int      gamePly;
+    uint64_t zkey;
+
+    struct Undo {
+        int      castlingRights;
+        Square   epSquare;
+        int      rule50;
+        uint64_t key;
+        Piece    captured;
+    };
+    Undo undoStack[1024];
+    int  undoCount;
+
+    uint64_t repKeys[1024];
+    int      repCount;
+};
+
+} // namespace chess
+
+#endif // CHESS_POSITION_H