code: func Int64(v []byte, err error) (int64, error) {
  	if err != nil {
  		return 0, err
  	} else if v == nil || len(v) == 0 {
  		return 0, nil
  	} else if len(v) != 8 {
  		return 0, errIntNumber
  	}
  
  	return int64(binary.LittleEndian.Uint64(v)), nil
  }
docs: /*
  	Below I forget why I use little endian to store int.
  	Maybe I was foolish at that time.
  */
  // Int64 gets 64 integer with the little endian format.