add custom chess engine

native/chess_engine/src/perft.cpp

@@ -0,0 +1,22 @@
+#include "perft.h"
+
+namespace chess {
+
+uint64_t perft(Position& pos, int depth) {
+    if (depth == 0) return 1;
+
+    MoveList list;
+    pos.generate_legal(list);
+
+    if (depth == 1) return uint64_t(list.size());
+
+    uint64_t nodes = 0;
+    for (Move m : list) {
+        pos.do_move(m);
+        nodes += perft(pos, depth - 1);
+        pos.undo_move(m);
+    }
+    return nodes;
+}
+
+} // namespace chess