engine/src/bitboard.c

@@ -715,6 +715,14 @@ bool apply_move_on_copy(struct Board *in, struct Board *out, struct Move m) {
         in->castling_rights, m.piece, m.from, m.to, captured_pid
     );
 
+
+    // Apply full and half move clock counts.
+    bool is_capture = (m.flags & MF_CAPTURE) || (m.flags & MF_ENPASSANT);
+    bool is_pawn    = (m.piece == P) || (m.piece == p);
+
+    out->halfmove_clock = (is_capture || is_pawn) ? 0 : in->halfmove_clock + 1;
+    out->fullmove_number = in->fullmove_number + (in->side_to_move == BLACK);
+
     // Side to move flips
     out->side_to_move = opp;