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 +1,134 @@
+#include "movegen.h"
+
+namespace chess {
+
+namespace {
+
+void add_promotions(MoveList& list, Square from, Square to) {
+    list.add(Move::make(from, to, PROMOTION, QUEEN));
+    list.add(Move::make(from, to, PROMOTION, ROOK));
+    list.add(Move::make(from, to, PROMOTION, BISHOP));
+    list.add(Move::make(from, to, PROMOTION, KNIGHT));
+}
+
+void generate_castling(const Position& pos, MoveList& list) {
+    if (pos.in_check()) return;
+
+    Color us = pos.side_to_move(), them = ~us;
+    Bitboard occ = pos.pieces();
+    auto attacked = [&](Square sq) { return (pos.attackers_to(sq) & pos.pieces(them)) != 0; };
+
+    if (us == WHITE) {
+        if (pos.can_castle(WHITE, KINGSIDE) &&
+            !(occ & (square_bb(F1) | square_bb(G1))) && !attacked(F1) && !attacked(G1))
+            list.add(Move::make(E1, G1, CASTLING));
+        if (pos.can_castle(WHITE, QUEENSIDE) &&
+            !(occ & (square_bb(B1) | square_bb(C1) | square_bb(D1))) && !attacked(D1) && !attacked(C1))
+            list.add(Move::make(E1, C1, CASTLING));
+    } else {
+        if (pos.can_castle(BLACK, KINGSIDE) &&
+            !(occ & (square_bb(F8) | square_bb(G8))) && !attacked(F8) && !attacked(G8))
+            list.add(Move::make(E8, G8, CASTLING));
+        if (pos.can_castle(BLACK, QUEENSIDE) &&
+            !(occ & (square_bb(B8) | square_bb(C8) | square_bb(D8))) && !attacked(D8) && !attacked(C8))
+            list.add(Move::make(E8, C8, CASTLING));
+    }
+}
+
+} // namespace
+
+void generate_pseudo(const Position& pos, MoveList& list) {
+    Color us = pos.side_to_move(), them = ~us;
+    Bitboard occ = pos.pieces();
+    Bitboard targets = ~pos.pieces(us);  // empty squares or enemy pieces
+    Bitboard theirs = pos.pieces(them);
+
+    // Pawns
+    int  push = (us == WHITE) ? 8 : -8;
+    Rank promoRank = (us == WHITE) ? RANK_8 : RANK_1;
+    Rank startRank = (us == WHITE) ? RANK_2 : RANK_7;
+    Bitboard b = pos.pieces(us, PAWN);
+    while (b) {
+        Square s = pop_lsb(b);
+        Square t = Square(int(s) + push);
+        if (!(occ & square_bb(t))) {
+            if (rank_of(t) == promoRank) {
+                add_promotions(list, s, t);
+            } else {
+                list.add(Move::make(s, t));
+                if (rank_of(s) == startRank) {
+                    Square t2 = Square(int(t) + push);
+                    if (!(occ & square_bb(t2))) list.add(Move::make(s, t2));
+                }
+            }
+        }
+        Bitboard caps = PawnAttacks[us][s] & theirs;
+        while (caps) {
+            Square c = pop_lsb(caps);
+            if (rank_of(c) == promoRank) add_promotions(list, s, c);
+            else                         list.add(Move::make(s, c));
+        }
+        if (pos.ep_square() != SQ_NONE && (PawnAttacks[us][s] & square_bb(pos.ep_square())))
+            list.add(Move::make(s, pos.ep_square(), EN_PASSANT));
+    }
+
+    // Knights
+    b = pos.pieces(us, KNIGHT);
+    while (b) {
+        Square s = pop_lsb(b);
+        Bitboard a = KnightAttacks[s] & targets;
+        while (a) list.add(Move::make(s, pop_lsb(a)));
+    }
+
+    // Bishops
+    b = pos.pieces(us, BISHOP);
+    while (b) {
+        Square s = pop_lsb(b);
+        Bitboard a = bishop_attacks(s, occ) & targets;
+        while (a) list.add(Move::make(s, pop_lsb(a)));
+    }
+
+    // Rooks
+    b = pos.pieces(us, ROOK);
+    while (b) {
+        Square s = pop_lsb(b);
+        Bitboard a = rook_attacks(s, occ) & targets;
+        while (a) list.add(Move::make(s, pop_lsb(a)));
+    }
+
+    // Queens
+    b = pos.pieces(us, QUEEN);
+    while (b) {
+        Square s = pop_lsb(b);
+        Bitboard a = queen_attacks(s, occ) & targets;
+        while (a) list.add(Move::make(s, pop_lsb(a)));
+    }
+
+    // King (non-castling)
+    {
+        Square s = pos.king_square(us);
+        Bitboard a = KingAttacks[s] & targets;
+        while (a) list.add(Move::make(s, pop_lsb(a)));
+    }
+}
+
+void Position::generate_legal(MoveList& list) {
+    list.count = 0;
+
+    MoveList pseudo;
+    generate_pseudo(*this, pseudo);
+
+    Color us = sideToMove;
+    for (Move m : pseudo) {
+        do_move(m);
+        // After do_move, sideToMove is the opponent; the move is legal iff the
+        // side that just moved did not leave its own king attacked.
+        bool legal = (attackers_to(king_square(us)) & pieces(sideToMove)) == 0;
+        undo_move(m);
+        if (legal) list.add(m);
+    }
+
+    generate_castling(*this, list); // already fully legal
+}
+
+} // namespace chess