#ifndef timerclear
#define timerclear(tvp)         (tvp)->tv_sec = (tvp)->tv_usec = 0
#endif

#ifndef timercmp
#define timercmp(tvp, uvp, cmp)                   \
        (((tvp)->tv_sec == (uvp)->tv_sec) ?       \
            ((tvp)->tv_usec cmp (uvp)->tv_usec) : \
            ((tvp)->tv_sec cmp (uvp)->tv_sec))
#endif

#ifndef timersub
#define timersub(tvp, uvp, vvp) \
        do { \
                (vvp)->tv_sec = (tvp)->tv_sec - (uvp)->tv_sec;    \
                (vvp)->tv_usec = (tvp)->tv_usec - (uvp)->tv_usec; \
                if ((vvp)->tv_usec < 0) {                         \
                        (vvp)->tv_sec--;                          \
                        (vvp)->tv_usec += 1000000;                \
                }                                                 \
        } while (0)
#endif