wip

C/pi.c

 /*
 * pi.c
 * Neil Gershenfeld 2/6/11
-* calculation of pi by a scalar sum
+* pi calculation benchmark
 * pi = 3.14159265358979323846
 */
 
 #include <stdio.h>
-#include <sys/time.h>
+#include <time.h>
 
 #define NPTS 1000000000
 
 void main() {
    int i;
-   double a,b,c,pi,mflops;
-   unsigned long int start_time,end_time;
-   struct timeval start,end;
+   double a,b,c,pi,dt,mflops;
+   struct timespec tstart,tend;
+   clock_gettime(CLOCK_REALTIME,&tstart);
    a = 0.5;
    b = 0.75;
    c = 0.25;
    pi = 0;
    pi = 0;
-   gettimeofday(&start, NULL);
    for (i = 1; i <= NPTS; ++i)
       pi += a/((i-b)*(i-c));
-   gettimeofday(&end, NULL);
-   start_time = start.tv_sec * 1e6 + start.tv_usec;
-   end_time = end.tv_sec * 1e6 + end.tv_usec;
-   mflops = NPTS*5.0/(end_time-start_time);
+   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 = %d, pi = %f\n",NPTS,pi);
-   printf("time = %f, estimated MFlops = %f\n",(end_time-start_time)/1.0e6,mflops);
+   printf("time = %f, estimated MFlops = %f\n",dt,mflops);
    }