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#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "omp.h"
OpenMP implementation example
Details of implementation/tutorial can be found here:
clock_t t, end;
double cpu_time_used;
// Structure for enabling reduction on the index of elements
struct Compare { int val; int index; };
// Custom reduction for finding hte index of the max element.
#pragma omp declare reduction(maximum : struct Compare : omp_out = omp_in.val > omp_out.val ? omp_in : omp_out)
void swap(int* a, int* b);
void selectionSort(int* A, int n);
void verify(int* A, int n);
int main(){
int number, iter =0;
int* Arr;
Arr = (int *)malloc( number * sizeof(int));
scanf("%d", &number);
for(; iter<number; iter++){
scanf("%d", &Arr[iter]);
t = clock();
selectionSort(Arr, number);
t = clock()-t;
for(int iter=0; iter<number;iter++){
printf("%d ", Arr[iter]);
cpu_time_used = ((double)t)/CLOCKS_PER_SEC;
// Verify if the algorithm works as advised
verify(Arr, number);
printf("\nTime taken for sort: %f", cpu_time_used);
return 0;
void selectionSort(int* A, int n){
for(int startpos =0; startpos < n; startpos++){
// Declare the structure required for reduction
struct Compare max;
// Initialize the variables
max.val = A[startpos];
max.index = startpos;
// Parallel for loop with custom reduction, at the end of the loop, max will have the max element and its index.
#pragma omp parallel for reduction(maximum:max)
for(int i=startpos +1; i< n; ++i){
if(A[i] > max.val){
max.val = A[i];
max.index = i;
swap(&A[startpos], &A[max.index]);
// Verification function
void verify(int* A, int n){
int failcount = 0;
for(int iter = 0; iter < n-1; iter++){
if(A[iter] < A[iter+1]){
printf("\nFail count: %d\n", failcount);
//Swap function
void swap(int* a, int* b){
int temp = *a;
*a = *b;
*b = temp;