gettimeofday(&t->end_time, 0);
t->real_sec = ((t->end_time.tv_sec - t->start_time.tv_sec) * 1000000.0 +
t->end_time.tv_usec - t->start_time.tv_usec) / 1000000;
gettimeofday(&t->end_time, 0);
t->real_sec = ((t->end_time.tv_sec - t->start_time.tv_sec) * 1000000.0 +
t->end_time.tv_usec - t->start_time.tv_usec) / 1000000;