add custom chess engine

native/chess_engine/src/uci.cpp

@@ -0,0 +1,50 @@
+#include "uci.h"
+
+#include <cstdlib>
+
+namespace chess {
+
+std::string move_to_uci(Move m) {
+    if (m == MOVE_NONE) return "0000";
+
+    Square f = m.from(), t = m.to();
+    std::string s;
+    s += char('a' + file_of(f));
+    s += char('1' + rank_of(f));
+    s += char('a' + file_of(t));
+    s += char('1' + rank_of(t));
+
+    if (m.type() == PROMOTION) {
+        static const char promo[PIECE_TYPE_NB] = { 0, 0, 'n', 'b', 'r', 'q', 0 };
+        s += promo[m.promotion()];
+    }
+    return s;
+}
+
+Move move_from_uci(const Position& pos, std::string_view uci) {
+    if (uci.size() < 4) return MOVE_NONE;
+
+    Square from = make_square(File(uci[0] - 'a'), Rank(uci[1] - '1'));
+    Square to   = make_square(File(uci[2] - 'a'), Rank(uci[3] - '1'));
+
+    if (uci.size() >= 5) {
+        PieceType promo = QUEEN;
+        switch (uci[4]) {
+            case 'q': promo = QUEEN;  break;
+            case 'r': promo = ROOK;   break;
+            case 'b': promo = BISHOP; break;
+            case 'n': promo = KNIGHT; break;
+        }
+        return Move::make(from, to, PROMOTION, promo);
+    }
+
+    Piece pc = pos.piece_on(from);
+    if (type_of(pc) == KING && std::abs(int(to) - int(from)) == 2)
+        return Move::make(from, to, CASTLING);
+    if (type_of(pc) == PAWN && to == pos.ep_square() && file_of(from) != file_of(to))
+        return Move::make(from, to, EN_PASSANT);
+
+    return Move::make(from, to);
+}
+
+} // namespace chess