Re: __TIME_MIN/__TIME_MAX

From: Bruce Evans (bde_at_zeta.org.au)
Date: 11/16/03

  • Next message: Jacques A. Vidrine: "Re: __TIME_MIN/__TIME_MAX" 
    Date: Sun, 16 Nov 2003 23:36:41 +1100 (EST)
To: "Jacques A. Vidrine" <nectar@FreeBSD.org>

    On Sun, 16 Nov 2003, Jacques A. Vidrine wrote:

    > On Sun, Nov 16, 2003 at 04:20:10AM -0600, Jacques A. Vidrine wrote:
    > > /* How can this be implemented correctly? */
    > > int range_error(long n, time_t t)
    > > {
    > > return (long)(t = n) == n;
    > > }
    >
    > Hrmp. Because time_t is probably signed, technically this can cause
    > `undefined behavior' if the range of `long' is more than the range of
    > `time_t' (e.g. on alpha). *sigh*

    Actually, it's implementation-defined if time_t is integral (doesn't
    matter if it is signed or unsigned) (and the value is not representable).
    It's only undefined if time_t is a floating type.

    > All I really want to do is correct a parsing bug and at the same time
    > eliminate a warning so that I can set WARNS?=1 in libc before the code
    > freeze.

    You can safely assume that it won't change to floating before the code
    freeze :-).

    I think (t = n) would cause compiler warnings at higher WARNS levels
    if time_t were unsigned. `t == n' certainly would.
    `(long)(time_t)n == n' could be used (this is like the above except it
    doesn't use a temporary variable. However, the cast to long breaks the
    warning about the bug that if n is -1L and time_t is unsigned long, then
    the comarison will succeed on 2's complement machines although time_t
    cannot represent -1.

    Bruce
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  • Next message: Jacques A. Vidrine: "Re: __TIME_MIN/__TIME_MAX"

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