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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <mpi.h>
  4.  
  5. #define ARRAY_SIZE 1000008 // Define the maximum array size statically
  6.  
  7. void prefix_sum(int* local_data, int local_size, int* result) {
  8.     int rank, size;
  9.     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  10.     MPI_Comm_size(MPI_COMM_WORLD, &size);
  11.  
  12.     // Compute local prefix sum
  13.     result[0] = local_data[0];
  14.     for (int i = 1; i < local_size; i++) {
  15.         result[i] = result[i - 1] + local_data[i];
  16.     }
  17.  
  18.     // Compute offset from previous ranks
  19.     int offset = 0;
  20.     if (rank != 0) {
  21.         int previous_sum;
  22.         MPI_Recv(&previous_sum, 1, MPI_INT, rank - 1, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
  23.         offset = previous_sum;
  24.         // Adjust the last element of the local prefix sum with the received offset
  25.         result[local_size - 1] += offset;
  26.         // Send the total sum of the current process to the next process
  27.         int total_sum = result[local_size - 1];
  28.         if (rank != size - 1) {
  29.             MPI_Send(&total_sum, 1, MPI_INT, rank + 1, 0, MPI_COMM_WORLD);
  30.         }
  31.         // Adjust all local results based on the offset
  32.         for (int i = 0; i < local_size - 1; i++) {
  33.             result[i] += offset;
  34.         }
  35.     }
  36.     // Send the total sum to the next rank
  37.     int total_sum = result[local_size - 1];
  38.     if (rank == 0) {
  39.         MPI_Send(&total_sum, 1, MPI_INT, rank + 1, 0, MPI_COMM_WORLD);
  40.     }
  41. }
  42.  
  43. int main(int argc, char** argv) {
  44.     MPI_Init(&argc, &argv);
  45.  
  46.     int rank, size;
  47.     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  48.     MPI_Comm_size(MPI_COMM_WORLD, &size);
  49.  
  50.     // Ensure ARRAY_SIZE is divisible by size
  51.     if (ARRAY_SIZE % size != 0) {
  52.         if (rank == 0) {
  53.             fprintf(stderr, "Array size must be divisible by the number of processes.\n");
  54.         }
  55.         MPI_Finalize();
  56.         return EXIT_FAILURE;
  57.     }
  58.  
  59.     int total_size = ARRAY_SIZE;
  60.     int data[ARRAY_SIZE]; // Static allocation for the entire array
  61.  
  62.     if (rank == 0) {
  63.         // Initialize array with ones
  64.         for (int i = 0; i < total_size; i++) {
  65.             data[i] = 1;
  66.         }
  67.     }
  68.  
  69.     // Compute local size for each process
  70.     int local_size = total_size / size;
  71.     int local_data[local_size]; // Static allocation for local data
  72.  
  73.     // Distribute data among processes
  74.     MPI_Scatter(data, local_size, MPI_INT, local_data, local_size, MPI_INT, 0, MPI_COMM_WORLD);
  75.  
  76.     // Measure computation time
  77.     double start_time = MPI_Wtime();
  78.  
  79.     // Compute prefix sum locally and adjust with offsets
  80.     int local_result[local_size]; // Static allocation for local result
  81.     prefix_sum(local_data, local_size, local_result);
  82.  
  83.     // Gather the results back
  84.     static int result[ARRAY_SIZE]; // Static allocation for the final result
  85.     MPI_Gather(local_result, local_size, MPI_INT, result, local_size, MPI_INT, 0, MPI_COMM_WORLD);
  86.  
  87.     double end_time = MPI_Wtime();
  88.  
  89.     // Print the result and computation time
  90.     if (rank == 0) {
  91.         printf("Prefix Sum: ");
  92.         printf("%d ", result[1000007]);
  93.         printf("\n");
  94.         printf("Computation Time: %f seconds\n", end_time - start_time);
  95.     }
  96.  
  97.     MPI_Finalize();
  98.     return 0;
  99. }
  100.  
Success #stdin #stdout #stderr 0.25s 40764KB
comments (?)
stdin 
Standard input is empty
stdout 
Standard output is empty
stderr 
Error: unexpected symbol in "void prefix_sum"
Execution halted
https://ideone.com/xWLvx0
language:
R (R 3.5.2)
created:
1 day ago
visibility:
public

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