enum class endian_t = { little, big };

static constexpr endian_t le = endian_t::little;
static constexpr endian_t be = endian_t::big;
static constexpr endian_t ne = *&((const char&) 1) ? le : be;

template <endian_t from, typename T>
T swap_from(const T& t) {
  if (from == ne)
    return t;
  return swap_bytes(t);
}