code: public static SingleItemSketch heapify(final Memory mem) {
      final long memPre0 = mem.getLong(0);
      checkDefaultBytes0to7(memPre0);
      return new SingleItemSketch(mem.getLong(8));
    }
docs: Creates a SingleItemSketch on the heap given a Memory and assumes the DEFAULT_UPDATE_SEED.
  @param mem the Memory to be heapified.  It must be a least 16 bytes.
  @return a SingleItemSketch