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* Neil Gershenfeld 6/21/19
* OpenMP pi calculation benchmark, with multiple iterations
* pi = 3.14159265358979323846
*/
#include <stdio.h>
#include <time.h>
#include <omp.h>
#include <stdint.h>
#define NPTS 1000000000
#define NLOOP 10
void main() {
uint64_t i;
int j;
double a,b,c,pi,dt,mflops,max;
struct timespec tstart,tend;
a = 0.5;
b = 0.75;
c = 0.25;
max = 0;
for (j = 0; j < NLOOP; ++j) {
pi = 0;
clock_gettime(CLOCK_REALTIME,&tstart);
#pragma omp parallel for reduction(+:pi)
for (i = 1; i <= NPTS; ++i)
pi += a/((i-b)*(i-c));
clock_gettime(CLOCK_REALTIME,&tend);
dt = (tend.tv_sec+tend.tv_nsec/1e9)-(tstart.tv_sec+tstart.tv_nsec/1e9);
mflops = NPTS*5.0/(dt*1e6);
printf("NPTS = %ld, pi = %f, threads = %d\n",NPTS,pi,omp_get_max_threads());
if (mflops > max) max = mflops;
printf("time = %f, estimated MFlops = %f, max = %f\n",dt,mflops,max);
}
}