a.cc

using uint16_t = unsigned short;
using  uint64_t = unsigned long long;

static_assert(sizeof(uint16_t) == 2);
static_assert(sizeof(uint64_t) == 8);

struct priority {
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
  uint16_t padding;
  uint16_t dynamic;
  uint16_t staticp;
  uint16_t index;
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
  uint16_t index;
  uint16_t staticp;
  uint16_t dynamic;
  uint16_t padding;
#endif

 bool operator<(const priority &other) const;
private:
 uint64_t tie() const
 {
   return uint64_t(index) << 48 | uint64_t(staticp) << 32 | uint64_t(dynamic) << 16 | uint64_t(padding);
 }

};

bool priority::operator<(const priority &other) const
{
   return tie() < other.tie();
   // This is not optimized:
//   return std::tie(index, staticp, dynamic, padding) < std::tie(other.index, other.staticp, other.dynamic, other.padding);
}