vyom_lodu

// CPP Program to multiply two matrix using pthreads
#include <bits/stdc++.h>
using namespace std;

// maximum size of matrix
#define MAX 4

// maximum number of threads
#define MAX_THREAD 4


int MX = 100;

int **matA, **matB, **matC;

int step_i = 0;
int n;

void* multi(void* arg)
{
    int core = step_i++;

    // Each thread computes 1/4th of matrix multiplication
    for (int i = core * n / 4; i < (core + 1) * n / 4; i++)
        for (int j = 0; j < n; j++)
            for (int k = 0; k < n; k++)
                matC[i][j] += matA[i][k] * matB[k][j];
}


// Driver Code
double job(int n)
{
    time_t start, end;

    matA = (int**)malloc(n*sizeof(int*));
    matB = (int**)malloc(n*sizeof(int*));
    matC = (int**)malloc(n*sizeof(int*));

    for (int i = 0; i < n; i++) {
        matA[i] = (int*)malloc(n*sizeof(int));
        matB[i] = (int*)malloc(n*sizeof(int));
        matC[i] = (int*)malloc(n*sizeof(int));
        for (int j = 0; j < n; j++) {
            matA[i][j] = rand() % MX;
            matB[i][j] = rand() % MX;
        }
    }

/** // Displaying matA
    cout << endl
        << "Matrix A" << endl;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++)
            cout << matA[i][j] << " ";
        cout << endl;
    }

    // Displaying matB
    cout << endl
        << "Matrix B" << endl;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++)
            cout << matB[i][j] << " ";
        cout << endl;
    }
**/
    // declaring four threads
    pthread_t threads[MAX_THREAD];

    time(&start);
    clock_t st, ed;
    st = clock();
    clock_t tic = clock();
    // Creating four threads, each evaluating its own part
    for (int i = 0; i < MAX_THREAD; i++) {
        int* p;
        pthread_create(&threads[i], NULL, multi, (void*)(p));
    }

    // joining and waiting for all threads to complete
    for (int i = 0; i < MAX_THREAD; i++)
        pthread_join(threads[i], NULL);
    clock_t toc = clock();
    ed = clock();
    time(&end);
    auto x =double(ed-st)/double(CLOCKS_PER_SEC);
    return (double)(toc - tic) / CLOCKS_PER_SEC;

    // Displaying the result matrix
    /**
    cout << endl
        << "Multiplication of A and B" << endl;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++)
            cout << matC[i][j] << " ";
        cout << endl;
    }
    **/

}

int main()
{
    for (int i = 1; i < 55; i++)
    {
        cout << "n : " << i*i << ", time :" << job(i*i) << endl;
    }

}