log-stats.h

 
#include <cmath>
 
class LogStats
    {
public:
    void add(double x)
        {
        x = std::log(x);
        n += 1;
        double delta1 = x - m;
        m += delta1 / n;
        double delta2 = x - m;
        s += delta1 * delta2;
        }
 
    long count() const { return n; }
 
    double mean() const { return std::exp(m); }
 
    double stddev() const { return std::sqrt(s / n); }
 
private:
    long n = 0;   
    double m = 0; 
    double s = 0; 
    };