Add a simple statistics calculator utility

libs/util/include/psemek/util/statistics.hpp

@@ -0,0 +1,87 @@
+#pragma once
+
+#include <cmath>
+#include <limits>
+
+namespace psemek::util
+{
+
+	namespace detail
+	{
+
+		template <typename T>
+		constexpr T min()
+		{
+			if constexpr (std::is_floating_point_v<T>)
+			{
+				return -std::numeric_limits<T>::infinity();
+			}
+			else
+			{
+				return std::numeric_limits<T>::min();
+			}
+		}
+
+		template <typename T>
+		constexpr T max()
+		{
+			if constexpr (std::is_floating_point_v<T>)
+			{
+				return std::numeric_limits<T>::infinity();
+			}
+			else
+			{
+				return std::numeric_limits<T>::max();
+			}
+		}
+
+	}
+
+	template <typename T>
+	struct statistics
+	{
+		void push(T const & value);
+
+		T mean() const;
+		T var() const;
+		T min() const { return min_; }
+		T max() const { return max_; }
+
+	private:
+		std::size_t count_ = 0;
+		T sum_ = T{0};
+		T sum_sqr_ = T{0};
+		T min_ = detail::max<T>();
+		T max_ = detail::min<T>();
+	};
+
+	template <typename T>
+	void statistics<T>::push(T const & value)
+	{
+		++count_;
+		sum_ += value;
+		sum_sqr_ += value * value;
+		min_ = std::min(min_, value);
+		max_ = std::max(max_, value);
+	}
+
+	template <typename T>
+	T statistics<T>::mean() const
+	{
+		return sum_ / count_;
+	}
+
+	template <typename T>
+	T statistics<T>::var() const
+	{
+		T const m = mean();
+		return std::sqrt(sum_sqr_ / count_ - m * m);
+	}
+
+	template <typename OStream, typename T>
+	OStream & operator << (OStream & os, statistics<T> const & s)
+	{
+		return os << "mean = " << s.mean() << ", var = " << s.var() << ", range = [" << s.min() << " .. " << s.max() << "]";
+	}
+
+}