1  extern void abort (void);
       2  
       3  struct S {
       4    unsigned b4:4;
       5    unsigned b6:6;
       6  } s;
       7  
       8  int main()
       9  {
      10    s.b6 = 31;
      11    s.b4 = s.b6;
      12    s.b6 = s.b4;
      13    if (s.b6 != 15)
      14      abort ();
      15    return 0;
      16  }
      17