class A
   {
     union {
       unsigned int _dummy_drc[2];
       struct {
         unsigned int _trans_drc :1;
         unsigned int _cap_drc :1;
         unsigned int _fanout_drc :1;
         unsigned int _trans_drc_index :10;
         unsigned int _cap_drc_index :10;
         unsigned int _fanout_drc_index :10;
      };
    };
  };

|1 |2 |3 |4 |5 |p |6 |p     field position, p stands for padding
|1 |1 |1 |10|10|8 |10|22    field bits
|1 |2 |3 |13|23|32|10|32    cumulative bits since start of object
|1                |2        underlying integer position