/* Streaming probe: checks whether the input arrays are already mapped memory
* (then streaming 80MB shows up as time but not as dirty pages). */
void count_2d(int n, const unsigned *x, const unsigned *y, unsigned *out) {
unsigned long long s = 0;
for (int i = 0; i < n; i++) s += (unsigned long long)x[i] + y[i];
if (n > 0) out[0] = (unsigned)s;
}