Optimising APSP

gistfile1.txt

        int a; int b; int c;

        for (k = 0; k < n; ++k) {
            for (i = 0; i < n; ++i) {
                a = d[i * n + k];
                if (a == INF) continue;
                for (j = 0; j < n; ++j) {
                    b = d[i * n + j];
                    c = d[k * n + j];
                    if (c == INF) continue;
                    else if (b == INF) d[i * n + j] = a + c;
                    else d[i * n + j] = a < b + c ? a : b + c;
                }
            }
        }