Re: __TIME_MIN/__TIME_MAX

From: Jacques A. Vidrine (nectar_at_FreeBSD.org)
Date: 11/16/03

  • Next message: Jacques A. Vidrine: "Re: __TIME_MIN/__TIME_MAX" 
    Date: Sun, 16 Nov 2003 04:20:10 -0600
To: Terry Lambert <tlambert2@mindspring.com>

    On Sat, Nov 15, 2003 at 02:37:03PM -0800, Terry Lambert wrote:
    > "Jacques A. Vidrine" wrote:
    > > In at least one place in libc, it is necessary to range check a time_t
    > > value. One most platforms, time_t has the same range as `int', but
    > > on at least amd64, it has a larger range. Any objections to adding
    > > definitions of __TIME_MIN and __TIME_MAX to sys/${arch}/_limits.h?
    > >
    > > I could just do the usual check for lossage after casting, except that
    > > in theory time_t could be a floating-point value (but not in reality
    > > in FreeBSD). It seems cleaner to me to have an explicit range.
    >
    > XSI: time_t and clock_t shall be integer or real-floating types.
    >
    > The range should be derived from th type. Defining separate values
    > outside the implementation namespace might be OK, but keeping those
    > values synchronized with the size_t is likely to be painful for
    > years to come.

    I don't think I understand your point. time_t and size_t have no
    relationship. The __TIME_MIN/__TIME_MAX I was suggesting would have
    been analogous to other numerical limits defined in <limits.h> such as
    INT_MIN/INT_MAX or our implementation-only __OFF_MIN/__OFF_MAX. Yes,
    they'd need to be synchronized with the actual type in use, e.g.

      #define __TIME_MAX __INT_MAX /* most platforms */
      #define __TIME_MAX __LONG_MAX /* ia64, amd64 */

    (Note that now, I don't intend to implement this because it doesn't
    actually help me get out of the quandry I was in. But, I still feel
    like discussing if anyone is interested :-)

    By the way, that quote from SUSv3 (``shall be integer or real-floating
    types'') is what messes me up. time_t could be signed or unsigned. If
    it were unsigned (extremely unlikely, but OK according to the letter of
    the standard), then I don't think I can detect certain range errors.

        /* How can this be implemented correctly? */
        int range_error(long n, time_t t)
        {
                return (long)(t = n) == n;
        }
        
    Too bad (IMHO) C never grew other operators like sizeof that let you
    examine type attributes.

    Cheers, 

    -- 
Jacques Vidrine   NTT/Verio SME      FreeBSD UNIX       Heimdal
nectar@celabo.org jvidrine@verio.net nectar@freebsd.org nectar@kth.se
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