TimerTest.cpp

#define NOMINMAX
#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>
#include <windows.h>
#include <stdint.h>
#include <math.h>
#include <float.h>
#include <algorithm>
#include <vector>

using u32 = uint32_t;
using u64 = uint64_t;

LARGE_INTEGER GFrequency;

inline u64 GetTimestamp()
{
	LARGE_INTEGER T;
	QueryPerformanceCounter(&T);
	return T.QuadPart;
}

inline double TicksToMS(double Ticks)
{
	return (Ticks*1000.0) / double(GFrequency.QuadPart);
}

inline double clamp(double x, double lower, double upper)
{
	return std::min(std::max(x, lower), upper);
}

template <typename T>
struct OnlineVariance
{
	int n = 0;
	T mean = T(0);
	T M2 = T(0);

	void addSample(T x)
	{
		n++;
		T delta = x - mean;
		mean = mean + delta / (float)n;
		M2 = M2 + delta * (x - mean);
	}

	T getVariance()
	{
		if (n < 2)
		{
			return T(0);
		}
		T variance = M2 / (float)(n - 1);
		return variance;
	}
};

int main()
{
	QueryPerformanceFrequency(&GFrequency);

	static constexpr u32 SampleCount = 10000;

	std::vector<double> Samples;
	Samples.reserve(SampleCount);

	double TMin = DBL_MAX;
	double TMax = 0;

	OnlineVariance<double> VarianceCalc;

	for (u32 i = 0; i < SampleCount; ++i)
	{
		u64 t0 = GetTimestamp();

		Sleep(4);

		u64 t1 = GetTimestamp();

		double dt = double(t1 - t0);
		VarianceCalc.addSample(dt);

		TMin = std::min(TMin, dt);
		TMax = std::max(TMax, dt);

		Samples.push_back(dt);
	}

	{
		static constexpr u32 BinCount = 50;
		u32 binsN[BinCount] = {};
		double binsX[BinCount] = {};

		FILE* f = fopen("output.csv", "w");
		for (double t : Samples)
		{
			u32 bin = u32(clamp(((t - TMin) / (TMax - TMin)) * double(BinCount), 0.0, BinCount-1));
			binsN[bin]++;
			binsX[bin] += t;
		}
		for (u32 i = 0; i < BinCount; ++i)
		{
			if (binsN[i])
			{
				double t = binsX[i] / binsN[i];
				fprintf(f, "%f, %d\n", TicksToMS(t), binsN[i]);
			}
		}

		fclose(f);
	}

	double Avg = TicksToMS(VarianceCalc.mean);
	double StdDev = TicksToMS(sqrt(VarianceCalc.getVariance()));

	printf("Mean: %.2f ms, StdDev: %.2f, Min: %.2f, Max: %.2f\n", Avg, StdDev, TicksToMS(TMin), TicksToMS(TMax));

	return 0;
}