Method m2

cpp/src/arrow/compute/kernels/aggregate_var_std_internal.h:49–56

  double mean() const { return static_cast<double>(sum) / count; }

  double m2() const {
    // calculate m2 = square_sum - sum * sum / count
    // decompose `sum * sum / count` into integers and fractions
    const int128_t sum_square = static_cast<int128_t>(sum) * sum;
    const int128_t integers = sum_square / count;
    const double fractions = static_cast<double>(sum_square % count) / count;
    return static_cast<double>(square_sum - integers) - fractions;
  }
};

enum class StatisticType { Var, Std, Skew, Kurtosis };