wnd_add_free_ext
wnd_add_free_ext(wnd, old_bits, new_bits - old_bits, false);
wnd_add_free_ext(wnd, wnd->zone_bit, zlen, false);
wnd_add_free_ext(wnd,
wnd_add_free_ext(wnd, wbit + wpos - prev_tail,
wnd_add_free_ext(wnd, wbit + wpos - prev_tail,
wnd_add_free_ext(wnd, wnd->nbits - prev_tail, prev_tail, true);
wnd_add_free_ext(wnd, bit, op, false);