docs: public ByteBuffer[] getBuffers(int start, int len)
      {
          if (len == 0)
          {
              return ar0;
          }
          if (len > capacity)
          {
              throw new IllegalArgumentException("len="+len+" > capacity="+capacity);
          }
          int s = start % capacity;
          int e = (start+len) % capacity;
          return getBuffersForSpan(s, e);
      }