tvsub
extern void tvsub(struct timeval *, struct timeval *);
(void) tvsub(&tv, tp);
(void) tvsub(&tv, tp);
(void) tvsub(&tv, tp);
(void) tvsub(&tv, tp);
tvsub(&diff, &pp->p_etime, &pp->p_btime);
tvsub(&td, t1, t0);
void tvsub(struct timeval *tdiff, struct timeval *t1, struct timeval *t0);