code: private int startFrame(final int offset, final int nLocal, final int nStack) {
          int n = 3 + nLocal + nStack;
          if (frame == null || frame.length < n) {
              frame = new int[n];
          }
          frame[0] = offset;
          frame[1] = nLocal;
          frame[2] = nStack;
          return 3;
      }
docs: Starts the visit of a stack map frame.
  
  @param offset
  the offset of the instruction to which the frame corresponds.
  @param nLocal
  the number of local variables in the frame.
  @param nStack
  the number of stack elements in the frame.
  @return the index of the next element to be written in this frame.