Cache lines

/**
 * Cache lines demo program --- notice the
 * the difference in runtime when accessing
 * the matrix row-wise / column-wise.
 */
#include <stdio.h>
#include <stdlib.h>

#define N 30000

int main(int argc, char *argv[])
{
    int i, j, sum = 0;
    if (argc < 2) { printf("Please supply 0 or 1 as an argument.\n"); return 1; }
    int** a = (int**) malloc(sizeof(int*) * N);
    for (i = 0; i < N; i++) {
        a[i] = (int*) malloc(sizeof(int) * N);
    }

    if (atoi(argv[1])) {
        for (j = 0; j < N; j++) {
            for (i = 0; i < N; i++) {
                sum += a[i][j];
            }
        }
    } else {
        for (i = 0; i < N; i++) {
            for (j = 0; j < N; j++) {
                sum += a[i][j];
            }
        }
    }
    printf("sum: %d\n", sum);

    for (i = 0; i < N; i++) {
        free(a[i]);
    }
    free(a);
}