Date: Thu, 1 Jul 2004 14:11:24 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Brian Fundakowski Feldman <green@freebsd.org> Cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/vm vm_map.c Message-ID: <20040701140025.C3068@gamplex.bde.org> In-Reply-To: <20040630080047.GC946@green.homeunix.org> References: <200406281915.i5SJFeaV060231@repoman.freebsd.org> <20040628193858.GG5635@green.homeunix.org> <20040629114614.T2908@gamplex.bde.org> <20040630095111.U2619@gamplex.bde.org> <20040630080047.GC946@green.homeunix.org>
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On Wed, 30 Jun 2004, Brian Fundakowski Feldman wrote: > On Tue, Jun 29, 2004 at 08:02:48PM -0700, David Schultz wrote: > > On Wed, Jun 30, 2004, Bruce Evans wrote: > > > On Tue, 29 Jun 2004, Andrew Gallatin wrote: > > > > > > > Bruce Evans writes: > > > > > MIN() and MAX() should not be used in the kernel. 4.4BSD removed them in > > > > > the kernel, but FreeBSD broke this in rev.1.141 of sys/param.h. They > > > > > remain removed in RELENG_4. > > > > > > > > OK. Then what's the correct fix? ulmin()? > > > > > > Fixing min() to handle all unsigned types is probably best. > > > > Hmm...but this means either > > > > a) slightly pessimizing 32-bit ports with a function on uintmax_t's, > > > > b) using a macro and introducing double-expansion problems, or > > > > c) using GCC extensions > > > > Option (c) seems best from a technical standpoint, except that > > we'd be making it harder than it already is to compile the kernel > > with compilers other than gcc and icc. (Do others have the > > statement expr extension?) > > No, the correct fix is using MIN() or MAX() that are well-documented > to provide the exact side-effects C programmers know to expect. They > automatically return the correct type, too, with no coercion! No. MIN() and MAX() are not documented. The don't even exist in the kernel in FreeBSD-[2-4]. They only return the correct type in some cases. E.g., the correct type and value for MIN((foo_t)1, (bar_t)-1) is unclear, since foo_t might be unsigned and bar_t might be signed, and/or have different sizes: Case foo_t is unsigned char and bar_t is signed char, and chars are smaller than ints: the result is MIN(1, -1) = -1 and has type int. Case foo_t is unsigned int and bar_t is signed int: the result is min(1u, -1) = UINT_MAX and has type unsigned int. So programmers must still be aware of the types of the operands if the operand types are significantly different. Brucehome | help
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