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    /*
    * mppi.c
    * Neil Gershenfeld 6/21/19
    
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    * OpenMP pi calculation benchmark
    
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    * pi = 3.14159265358979323846
    */
    
    #include <stdio.h>
    #include <time.h>
    #include <omp.h>
    
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    #include <stdint.h>
    
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    #define NPTS 100000000000
    
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    void main() {
    
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       uint64_t i;
    
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       double a,b,c,pi,dt,mflops;
    
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       struct timespec tstart,tend;
       clock_gettime(CLOCK_REALTIME,&tstart);
       a = 0.5;
       b = 0.75;
       c = 0.25;
       pi = 0;
       pi = 0;
    
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       #pragma omp parallel for reduction(+:pi)
    
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       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);
    
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       printf("NPTS = %ld, pi = %f, threads = %d\n",NPTS,pi,omp_get_max_threads());
    
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       printf("time = %f, estimated MFlops = %f\n",dt,mflops);
       }