OpenCV数字图像处理九：使用opencv进行图像处理时准确测定处理时间 比opencv自带的准

#include <stdio.h>
#include <math.h>
#include <omp.h>
#include <windows.h>
LARGE_INTEGER m_liPerfFreq;
LARGE_INTEGER m_liPerfStart;
LARGE_INTEGER liPerfNow;
double dfTim;
void getStartTime()
{
QueryPerformanceFrequency(&m_liPerfFreq);
QueryPerformanceCounter(&m_liPerfStart);
}


void getEndTime()
{
QueryPerformanceCounter(&liPerfNow);
dfTim=( ((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * 1000.0f)/m_liPerfFreq.QuadPart);
}


void main()
{
static long num_steps = 1000000;
double step, pi;
double x, sum=0.0;
int i=0;
step = 1.0/(double)num_steps;
getStartTime();


//#pragma omp parallel for private(x) reduction(+:sum)
for (i=0; i<num_steps; i++)
{
x = (i+0.5)*step;
sum += 4.0/(1.0+x*x);
//printf("%f,%d\n",omp_get_thread_num());
}
getEndTime();
printf("%f\n",dfTim);
pi = step * sum;
printf ("pi=%f\n",pi);


}