add custom chess engine

native/chess_engine/src/zobrist.h

@@ -0,0 +1,21 @@
+// Zobrist hashing keys. Filled once by Zobrist::init() (from engine_create).
+// Position maintains the running key incrementally in do_move/undo_move.
+#ifndef CHESS_ZOBRIST_H
+#define CHESS_ZOBRIST_H
+
+#include "types.h"
+
+namespace chess {
+namespace Zobrist {
+
+extern uint64_t psq[PIECE_NB][SQUARE_NB];
+extern uint64_t enpassant[FILE_NB];
+extern uint64_t castling[16];
+extern uint64_t side;
+
+void init();
+
+} // namespace Zobrist
+} // namespace chess
+
+#endif // CHESS_ZOBRIST_H