checkNotNull(factory);
    return new ByteSourceFactory() {
      @Override
      public ByteSource createSource(byte[] bytes) throws IOException {
        return factory.createSource(bytes).slice(off, len);
      }

      @Override
      public byte[] getExpected(byte[] bytes) {
        byte[] baseExpected = factory.getExpected(bytes);
        int startOffset = (int) Math.min(off, baseExpected.length);

      return array.length;
    }
  }

  /**
   * Implementation of Striped where up to 2^k stripes can be represented, using an
   * AtomicReferenceArray of size 2^k. To map a user key into a stripe, we take a k-bit slice of the
   * user key's (smeared) hashCode(). The stripes are lazily initialized and are weakly referenced.
   */
  @VisibleForTesting
  static class SmallLazyStriped<L> extends PowerOfTwoStriped<L> {