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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <omp.h>
  4.  
  5. #define N 1000  // Size of the array
  6.  
  7. void prefix_sum(int* input, int* output, int n) {
  8.     #pragma omp parallel
  9.     {
  10.         int* temp = (int*)malloc(n * sizeof(int));  // Temporary storage for prefix sums in each thread
  11.  
  12.         // Copy input data to temporary array in parallel
  13.         #pragma omp for schedule(static)
  14.         for (int i = 0; i < n; i++) {
  15.             temp[i] = input[i];
  16.         }
  17.  
  18.         // Compute prefix sums
  19.         for (int step = 1; step < n; step *= 2) {
  20.             #pragma omp for schedule(dynamic) private(i)
  21.             for (int i = step; i < n; i++) {
  22.                 temp[i] += temp[i - step];
  23.             }
  24.             #pragma omp barrier  // Synchronize threads after each step to ensure correct calculations
  25.         }
  26.  
  27.         // Copy results to the output array
  28.         #pragma omp for schedule(static)
  29.         for (int i = 0; i < n; i++) {
  30.             output[i] = temp[i];
  31.         }
  32.  
  33.         free(temp);  // Deallocate memory for temporary array
  34.     }
  35. }
  36.  
  37. int main() {
  38.     int input[N];
  39.     int output[N];
  40.  
  41.     // Initialize the input array with values 1, 2, 3, ..., N
  42.     #pragma omp parallel for
  43.     for (int i = 0; i < N; i++) {
  44.         input[i] = i + 1;
  45.     }
  46.  
  47.     // Calculate prefix sums
  48.     prefix_sum(input, output, N);
  49.  
  50.     // Output the result (print the first few elements for brevity)
  51.     printf("Prefix sums:\n");
  52.     for (int i = 0; i < 10; i++) {
  53.         printf("%d ", output[i]);
  54.     }
  55.     printf("\n");
  56.  
  57.     return 0;
  58. }
  59.  
Success #stdin #stdout 0s 5280KB
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stdin
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Standard input is empty
stdout
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Prefix sums:
1 3 7 13 23 37 57 83 119 165
https://ideone.com/Sqpmhs
language:
C (gcc 8.3)
created:
5 days ago
visibility:
public

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