code: void addToSubroutine(final long id, final int nbSubroutines) {
          if ((status & VISITED) == 0) {
              status |= VISITED;
              srcAndRefPositions = new int[nbSubroutines / 32 + 1];
          }
          srcAndRefPositions[(int) (id >>> 32)] |= (int) id;
      }
docs: Marks this basic block as belonging to the given subroutine.
  
  @param id
  a subroutine id.
  @param nbSubroutines
  the total number of subroutines in the method.