code: func NewTarSumHash(r io.Reader, dc bool, v Version, tHash THash) (TarSum, error) {
  	headerSelector, err := getTarHeaderSelector(v)
  	if err != nil {
  		return nil, err
  	}
  	ts := &tarSum{Reader: r, DisableCompression: dc, tarSumVersion: v, headerSelector: headerSelector, tHash: tHash}
  	err = ts.initTarSum()
  	return ts, err
  }
docs: // NewTarSumHash creates a new TarSum, providing a THash to use rather than
  // the DefaultTHash.