Date: Sat, 12 Aug 2017 20:59:23 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> Cc: freebsd-bugs@freebsd.org Subject: Re: [Bug 221418] FreeBSD 10.4-PRERELEASE fails to build on systems using 32 bit time_t since r322315. Message-ID: <20170812204159.O1958@besplex.bde.org> In-Reply-To: <bug-221418-8-8Qobma2zSB@https.bugs.freebsd.org/bugzilla/> References: <bug-221418-8@https.bugs.freebsd.org/bugzilla/> <bug-221418-8-8Qobma2zSB@https.bugs.freebsd.org/bugzilla/>
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On Fri, 11 Aug 2017 a bug that doesn't want replies@freebsd.org wrote: > --- Comment #1 from Conrad Meyer <cem@freebsd.org> --- > Truncated INT64_MIN should be INT32_MIN on 2's complement, not 0. Seems like > we just lack a (time_t) cast on the value. Truncated INT64_MIN should be and is, 0 in 2's complement, since all of its low 32 bits are 0. In 1's complement, it should be -0, since all of its low 32 bits are 1. Casting to time_t is no different to assigning to time_t, except compilers usually only warn about overflow for the assignent. Casting thus enlarges the bug by breaking the warning about overflow. Related to this, the special value for possibly-invalid time_t's is ((time_t)-1), not some large negative value. This is large and positive if time_t is unsigned. In POSIX, times before the Epoch are invalid, but (time_t)-1) might be valid if it is positive. In Standard C, (time_t)-1) might be valid even if it is -1. I think the code needs a large negative value for technical reasons. INT64_MIN is very bogus for this, since 69 years in the past given by INT32_MIN should be enough for anyone, and further in the past than that is unrepresentable by time_t on systems with 32-bit signed time_t. If time_t is unsigned, no negative values are representable, so casts to int but not to time_t might be needed. > With regards to your patch, CHAR_BIT is always 8 on FreeBSD. CHAR_BIT is 8 on all POSIX systems later than 2001. CHAR_BIT is often spelled NBBY in BSD. NBBY is less verbose than CHAR_BIT and less cryptic than 8. Bruce
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