  void ReadValue(int64 batch, int64 n, uint64* out) const override {
    CopyToFingerprint(values_(row_splits_[batch] + n), out);
  }
  void ReadValue(int64 batch, int64 n, uint64* out) const override {
    CopyToFingerprint(values_(row_splits_[batch] + n), out);
  }