matrix_multiply.c

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

#define n 4096

double A[n][n];
double B[n][n];
double C[n][n];

float time_difference(struct timeval *start, 
        struct timeval *end) {
    return (end->tv_sec - start->tv_sec) 
            + 1e-6*(end->tv_usec - start->tv_usec);
}

int main(int argc, const char *argv[]) {
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            A[i][j] = (double)rand() / (double)RAND_MAX;
            B[i][j] = (double)rand() / (double)RAND_MAX;
            C[i][j] = 0;
        }
    }

    struct timeval start, end;
    gettimeofday(&start, NULL);

    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            for (int k = 0; k < n; ++k) {
                C[i][j] += A[i][k] * B[k][j];
            }
        }
    }

    gettimeofday(&end, NULL);
    printf("%0.6f seconds\n", time_difference(&start, &end));

    return 0;
}