module BinData::Struct::ByteAlignPlugin

def sum_num_bytes_below_index(index)
  sum = 0
  @field_objs.each_with_index do |obj, i|
    next unless include_obj?(obj)
    if align_obj?(obj)
      sum = sum.ceil + bytes_to_align(obj, sum.ceil)
    end
    break if i >= index
    nbytes = obj.do_num_bytes
    sum = (nbytes.is_a?(Integer) ? sum.ceil : sum) + nbytes
  end
  sum
end