int eval_surrounders(const libataxx::Position & pos_in)
{
        int score = 0;

        for(const auto & sq : pos_in.us()) {
                const auto destinations_s = libataxx::Bitboard{sq}.singles() & pos_in.us();
                score += destinations_s.count() == 8;

                const auto destinations_d = libataxx::Bitboard{sq}.doubles() & pos_in.us();
                score += (destinations_d.count() == 16) * 2;
        }

        for(const auto & sq : pos_in.them()) {
                const auto destinations_s = libataxx::Bitboard{sq}.singles() & pos_in.them();
                score -= destinations_s.count() == 8;

                const auto destinations_d = libataxx::Bitboard{sq}.doubles() & pos_in.them();
                score -= (destinations_d.count() == 16) * 2;
        }

        return score;
}