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Date: Tue, 14 Mar 2000 16:50:13 +0000
From: Paul Richards <paul@originative.co.uk>
Organization: Originative Solutions Ltd
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To: Bruce Evans <bde@zeta.org.au>
Cc: John Polstra <jdp@polstra.com>, current@FreeBSD.ORG
Subject: Re: MAX_UID ?
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Bruce Evans wrote:
> 
> On Sun, 12 Mar 2000, John Polstra wrote:
> 
> > Sheesh, criticism isn't enough?  Now it has to be constructive too? ;-)
> >
> > I guess it could go into <machine/limits.h> in the
> > "!defined(_ANSI_SOURCE)" section.  Bruce might have a better idea.

Trying to draw some closure on this discussion.

> 
> This is the same as putting it in <limits.h> in the
> "!defined(_ANSI_SOURCE)" section.  Anyway, the names should be FOO_MAX,
> not MAX_FOO.
> 
> In C99, there are about 50 *_MAX and *_MIN values defined in <stdint.h>
> for Standard C types alone.
> 
> I would prefer standard maxof() and minof() interfaces that work on
> any arithmetic type.  These can almost be written in portable C, at
> least in C89 where types are restricted to char, signed char, ...,
> long double:
> 
> #define isfloat(type)   ((type)0.5 != 0)
> #define issigned(type)  ((type)-1 < 0)
> #define isschar(type)   (!isfloat(type) && issigned(type) && sizeof(type) == 1)
> #define isuchar(type)   (!isfloat(type) && !issigned(type) && sizeof(type) == 1)
> ...
> #define maxof(type)     ((type)(isschar(type) ? SCHAR_MAX :
>                                 isuchar(type) ? UCHAR_MAX ...))

Where do you think these macros should go then?

Having though about this some more, although the above macros are useful
and can be used in a lot of the places where bounds checking needs to be
done, there is still probably a need to define certain constants, such
as UID_MAX, because the range of valid values may not necessarily be the
same as the range of values supported by the type.

UID_MAX being a good example, since FreeBSD does not support 32-bit UIDs
at the moment even though the kernel does. Most applications are
limiting themselves to USHRT_MAX, those applications should be fixed to
use UID_MAX, even if we still limit UID_MAX == USHRT_MAX for backwards
compatibility.

So, <sys/syslimits.h> seems like the right place for constants like
UID_MAX. Any disagreements there?

I guess the above macros should really be machine specific if we're
going to be pedantic. Would <machine/limits.h> be an appropriate
location for them?

Paul.


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