Centre Blaise Pascal » Bench4GPU

//

// Estimation of Pi using Monte Carlo exploration process

// gcc -std=c99 -O3 -o Pi Pi.c -lm 

//

#include <math.h>

#include <stdio.h>

#include <stdlib.h>

#include <mpi.h>

// Marsaglia RNG very simple implementation

#define znew  ((z=36969*(z&65535)+(z>>16))<<16)

#define wnew  ((w=18000*(w&65535)+(w>>16))&65535)

#define MWC   (znew+wnew)

#define SHR3  (jsr=(jsr=(jsr=jsr^(jsr<<17))^(jsr>>13))^(jsr<<5))

#define CONG  (jcong=69069*jcong+1234567)

#define KISS  ((MWC^CONG)+SHR3)

#define MWCfp MWC * 2.328306435454494e-10f

#define KISSfp KISS * 2.328306435454494e-10f

#define ITERATIONS 1000000000

#ifdef LONG

#define LENGTH unsigned long

#else

#define LENGTH unsigned int

#endif

LENGTH MainLoopGlobal(LENGTH iterations,unsigned int seed_w,unsigned int seed_z)

{

   unsigned int z=seed_z;

   unsigned int w=seed_w;

   unsigned  long total=0;

   for (LENGTH i=0;i<iterations;i++) {

      float x=MWCfp ;

      float y=MWCfp ;

      // Matching test

      int inside=((x*x+y*y) < 1.0f) ? 1:0;

      total+=inside;

   }

   return(total);

}

int main(int argc, char *argv[]) {

  unsigned int seed_w=10,seed_z=10;

  LENGTH iterations=ITERATIONS,inside[1024],insides,part_inside,part_iterations;

  int numtasks,rank,rc,tag=1,i;

  float pi;

  MPI_Status Stat;

  rc = MPI_Init(&argc,&argv);

  if (rc != MPI_SUCCESS) {

    printf ("Error starting MPI program. Terminating.\n");

    MPI_Abort(MPI_COMM_WORLD, rc);

  }

  MPI_Comm_size(MPI_COMM_WORLD,&numtasks);

  MPI_Comm_rank(MPI_COMM_WORLD,&rank);

  if (rank==0) {

    if (argc > 1) {

      iterations=(LENGTH)atol(argv[1]);

    }

    else {

      printf("\n\tPi : Estimate Pi with Monte Carlo exploration\n\n");

      printf("\t\t#1 : number of iterations (default 1 billion)\n\n");

    }

    part_iterations=iterations/numtasks;

    // Split part of code

    for (i=1;i<numtasks;i++) {

      rc = MPI_Send(&part_iterations, 1, MPI_UNSIGNED_LONG, i, tag, 

                    MPI_COMM_WORLD);

    }

    insides=MainLoopGlobal(part_iterations,seed_w,seed_z);

    printf("\tOn %i, find %lu inside\n",rank,(unsigned long)insides);

    // Join part of code

    for (i=1;i<numtasks;i++) {

      rc = MPI_Recv(&inside[i], 1, MPI_UNSIGNED_LONG, i, tag, 

                    MPI_COMM_WORLD, &Stat);

      printf("\tReceive %lu inside from %i\n",(unsigned long)inside[i],i);

      insides+=inside[i];

    }

    pi=4.*(float)insides/(float)((iterations/numtasks)*numtasks);

    printf("\n\tPi=%f with error %f and %lu iterations\n\n",pi,

           fabs(pi-4*atan(1))/pi,(unsigned long)iterations);

  }

  else

    {

      // Receive information from master

      rc = MPI_Recv(&part_iterations, 1, MPI_UNSIGNED_LONG, 0, tag, 

                    MPI_COMM_WORLD, &Stat);

      printf("\tOn %i, receive from master %lu\n",

             rank,(unsigned long)part_iterations);

      part_inside=MainLoopGlobal(part_iterations,seed_w,seed_z);

      printf("\tOn %i, find %lu inside\n",rank,(unsigned long)part_inside);

      rc = MPI_Send(&part_inside, 1, MPI_UNSIGNED_LONG, 0, tag, MPI_COMM_WORLD);

    }

  MPI_Finalize();

}