Word mb = Word.fromInt((int) (bytes >> LOG_BYTES_IN_MBYTE));
Word mb = Word.fromIntSignExtend((int) (bytes >> LOG_BYTES_IN_MBYTE));
  private static Extent getFracAvailable(float frac) {    long bytes = (long) (frac * AVAILABLE_BYTES.toLong());    Word mb = Word.fromInt((int) (bytes >> LOG_BYTES_IN_MBYTE));    Extent rtn = mb.lsh(LOG_BYTES_IN_MBYTE).toExtent();    return chunkAlign(rtn, false);  }