stddev.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <omp.h>
#include <sys/time.h>

double clock()
{
    struct timeval Tp;
    int stat;
    stat = gettimeofday(&Tp, NULL);
    if (stat != 0)
        printf("Error return from gettimeofday: %d", stat);
    return (Tp.tv_sec + Tp.tv_usec * 1.0e-6);
}

void kernel()
{
    static float std_dev[100 + 2] = { 0 }, data[100 + 2][100 + 2] = { 0 }, mean[100 + 2] = { 0 };
#pragma omp parallel
    {

#pragma omp for
        for (int x = 0; x <= 100; x++) {
            for (int k = 0; k <= 100; k++) {
#pragma omp atomic
                mean[x] += data[k][x] / 100;
            }

        }
#pragma omp for
        for (int t = 0; t <= 100; t++) {
            for (int k = 0; k <= 100; k++) {
#pragma omp atomic
                std_dev[t] += ((data[k][t] - mean[t]) * (data[k][t] - mean[t])) / 99;
            }

        }
#pragma omp for
        for (int p = 0; p <= 100; p++) {
#pragma omp atomic write
            std_dev[p] = sqrt(std_dev[p]);
        }
    }
}

int main()
{
    double start = 0.0, end = 0.0;
    start = clock();
    kernel();
    end = clock();
    printf("Total time taken  = %fs\n", end - start);
    return 0;
}