multitask.cpp

#include <iostream>
#include <omp.h>
#include <math.h>

const double PI = 3.141592653589793238463;
using namespace std;

int num_threads, upper_bound;

bool isPrime(int num) {
    for (int i=2; i<num; i++) {
        if (num % i == 0) {
            return false;
        }
    }
    return true;
}

/**
 * Gets an array of Prime numbers with size `num`
 * Eg:- prime_table(100) - Will generate first 100 prime numbers from [2, 3, ...]
 */
int* prime_table(int num) {
    int* primes = new int[num]; // Allocate memory for table
    int prime_number = 2, i = 0;

    while (i < num) {
        if (isPrime(prime_number)) {
            primes[i] = prime_number;
            i++;
        }
        prime_number++;
    }

    return primes;
}

/**
 * Computes sine table
 * Taken from - https://people.sc.fsu.edu/~jburkardt/c_src/multitask_openmp/multitask_openmp.c
 * PS: Not sure what this gives as output, some Expensive operation!!
 *     Do rise an Issue at https://github.com/nowke/hpc_lab/issues/new if you know the answer!
 */
double* sine_table(int num) {
    double* sines = new double[num];
    double a;

    #pragma omp parallel for private(a) num_threads(num_threads)
    for (int i=0; i<num; i++) {
        sines[i] = 0.0;
        for (int j=0; j <= i; j++) {
            a = j * PI / (num - 1);
            sines[i] += sin(a);
        }
    }
    return sines;
}

int main(int argc, char* argv[]) {

    if (argc < 3) {
        cout << "Usage: ./multitask.o upper_bound num_threads" << endl;
        return 1;
    }

    upper_bound = atoi(argv[1]);
    num_threads = atoi(argv[2]);
    int* primes;
    double* sines;

    // Time Variables
    double start_time = omp_get_wtime();
    double task1_start, task2_start, task1_end, task2_end;

    #pragma omp parallel sections num_threads(num_threads)
    {
        #pragma omp section
        {
            task1_start = omp_get_wtime();
            primes = prime_table(upper_bound);
            task1_end = omp_get_wtime();
        }
        #pragma omp section
        {
            task2_start = omp_get_wtime();
            sines = sine_table(upper_bound);
            task2_end = omp_get_wtime();
        }
    }

    double end_time = omp_get_wtime();

    cout << "Largest Prime: " << primes[upper_bound - 1] << endl;
    cout << "Largest Sine: " << sines[upper_bound - 1] << endl;
    cout << "Total Time: " << end_time - start_time << "s" << endl;
    cout << "Task 1 Time: " << task1_end - task1_start << "s" << endl;
    cout << "Task 2 Time: " << task2_end - task2_start << "s" << endl;

    return 0;
}