Re: [LEAPSECS] Lets get REAL about time.

[Paul J. Ste. Marie]

On 1/22/2012 7:42 AM,  Clive D.W. Feather wrote:
#define timespecsub(vvp, uvp)            \
     ((vvp)->tv_sec -= (uvp)->tv_sec,     \
      (vvp)->tv_nsec -= (uvp)->tv_nsec,   \
      ((vvp)->tv_nsec<  0)                \
       ? ((vvp)->tv_sec--, (vvp)->tv_nsec += 1000000000) \
       : (void) 0)
This has the advantage of being usable wherever a function can appear.

Not really.  For example &timespecsub doesn't work.  The do-while kludge 
can at least protect the arguments, eg:

#define timespecsub(vvp1, uvp1)                                 \
        do {                                                    \
                const struct timespec *vvp = vvp1;              \
                const struct timespec *uvp = uvp1;              \
                (vvp)->tv_sec -= (uvp)->tv_sec;                 \
                (vvp)->tv_sec -= (uvp)->tv_sec;                 \
                (vvp)->tv_sec -= (uvp)->tv_sec;                 \
                (vvp)->tv_nsec -= (uvp)->tv_nsec;               \
                if ((vvp)->tv_nsec < 0) {                       \
                        (vvp)->tv_sec--;                        \
                        (vvp)->tv_nsec += 1000000000;           \
                }                                               \
        } while (0)

and aside from not having an address otherwise behaves like a void function.

--
        --Paul

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