Improve C function performance with cache locality?

Question

I have to find a diagonal difference in a matrix represented as 2d array and the function prototype is

int diagonal_diff(int x[512][512])

I

Answer 1

With one minor change you can have your loops only operate on the desired indices. I just changed the j loop initialization.

int i, j, result = 0;
for (i = 0; i < 4; ++i) {
    for (j = i + 1; j < 4; ++j) {
        result += abs(array[i][j] - array[j][i]);
    }
}