CLOCKS_PER_SEC
NEW_AUX_ENT(AT_CLKTCK, CLOCKS_PER_SEC);
NEW_AUX_ENT(AT_CLKTCK, CLOCKS_PER_SEC);
while ((clock() - start_clock) * 1000 / CLOCKS_PER_SEC
printf("Clocks per second: %ld\n", CLOCKS_PER_SEC);
printf("time spent = %f\n", (double)(end - begin) / CLOCKS_PER_SEC);