private static long rawIndex(final long[] ary, final int idx) {
      assert idx >= 0 && idx < ary.length;
      return _Lbase + (idx * (long)_Lscale);
    }
Standard Java {@link Iterator}.  Not very efficient because it
auto-boxes the returned values.
jctools-core/src/main/java/org/jctools/maps/NonBlockingSetInt.java