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  1. #include "mpi.h"
  2. #include <stdio.h>
  3. #include <stdlib.h>
  4. #include <math.h>
  5.  
  6. #define LIMIT     2500000     /* Increase this to find more primes */
  7. #define FIRST     0           /* Rank of first task */
  8.  
  9. int prime(int n) {
  10. int i,squareroot;
  11. if (n>10) {
  12.    squareroot = (int) sqrt(n);
  13.    for (i=3; i<=squareroot; i=i+2)
  14.       if ((n%i)==0)
  15.          return 0;
  16.    return 1;
  17.    }
  18. /* Assume first four primes are counted elsewhere. Forget everything else */
  19. else
  20.    return 0;
  21. }
  22.  
  23.  
  24. int main (int argc, char *argv[])
  25. {
  26. int   ntasks,               /* total number of tasks in partitiion */
  27.       rank,                 /* task identifier */
  28.       n,                    /* loop variable */
  29.       pc,                   /* prime counter */
  30.       pcsum,                /* number of primes found by all tasks */
  31.       foundone,             /* most recent prime found */
  32.       maxprime,             /* largest prime found */
  33.       mystart,              /* where to start calculating */
  34.       stride;               /* calculate every nth number */
  35.  
  36. double start_time,end_time;
  37.  
  38. MPI_Init(&argc,&argv);
  39. MPI_Comm_rank(MPI_COMM_WORLD,&rank);
  40. MPI_Comm_size(MPI_COMM_WORLD,&ntasks);
  41. if (((ntasks%2) !=0) || ((LIMIT%ntasks) !=0)) {
  42.    printf("Sorry - this exercise requires an even number of tasks.\n");
  43.    printf("evenly divisible into %d.  Try 4 or 8.\n",LIMIT);
  44.    MPI_Finalize();
  45.    exit(0);
  46.    }
  47.  
  48. start_time = MPI_Wtime();   /* Initialize start time */
  49. mystart = (rank*2)+1;       /* Find my starting point - must be odd number */
  50. stride = ntasks*2;          /* Determine stride, skipping even numbers */
  51. pc=0;                       /* Initialize prime counter */
  52. foundone = 0;               /* Initialize */
  53.  
  54. /******************** task with rank 0 does this part ********************/
  55. if (rank == FIRST) {
  56.    printf("Using %d tasks to scan %d numbers\n",ntasks,LIMIT);
  57.    pc = 4;                  /* Assume first four primes are counted here */
  58.    for (n=mystart; n<=LIMIT; n=n+stride) {
  59.       if (isprime(n)) {
  60.          pc++;
  61.          foundone = n;
  62.          /***** Optional: print each prime as it is found
  63.          printf("%d\n",foundone);
  64.          *****/
  65.          }
  66.       }
  67.    MPI_Reduce(&pc,&pcsum,1,MPI_INT,MPI_SUM,FIRST,MPI_COMM_WORLD);
  68.    MPI_Reduce(&foundone,&maxprime,1,MPI_INT,MPI_MAX,FIRST,MPI_COMM_WORLD);
  69.    end_time=MPI_Wtime();
  70.    printf("Done. Largest prime is %d Total primes %d\n",maxprime,pcsum);
  71.    printf("Wallclock time elapsed: %.2lf seconds\n",end_time-start_time);
  72.    }
  73.  
  74.  
  75. /******************** all other tasks do this part ***********************/
  76. if (rank > FIRST) {
  77.    for (n=mystart; n<=LIMIT; n=n+stride) {
  78.       if (isprime(n)) {
  79.          pc++;
  80.          foundone = n;
  81.          /***** Optional: print each prime as it is found
  82.          printf("%d\n",foundone);
  83.          *****/
  84.          }
  85.       }
  86.    MPI_Reduce(&pc,&pcsum,1,MPI_INT,MPI_SUM,FIRST,MPI_COMM_WORLD);
  87.    MPI_Reduce(&foundone,&maxprime,1,MPI_INT,MPI_MAX,FIRST,MPI_COMM_WORLD);
  88.    }
  89.  
  90. MPI_Finalize();
  91. }
  92.  
Success #stdin #stdout #stderr 0.26s 39436KB
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stdin
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34
stdout
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Standard output is empty
stderr
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Error: unexpected symbol in "int prime"
Execution halted
https://ideone.com/YyogIE
language:
R (R 3.5.2)
created:
4 years ago
visibility:
public

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