linux-kernel - Re: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp

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Message-Id: <1205343249.8603.23.camel@brick>
Date:	Wed, 12 Mar 2008 10:34:09 -0700
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	Michael Buesch <mb@...sch.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jeff Garzik <jeff@...zik.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>
Subject: Re: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val()
	macros

On Wed, 2008-03-12 at 18:20 +0100, Michael Buesch wrote:
> On Wednesday 12 March 2008 17:54:26 Harvey Harrison wrote:
> > On Wed, 2008-03-12 at 16:13 +0100, Michael Buesch wrote:
> > > So why not call it clamp_const()?
> > > One could even use __builtin_constant_p() and make clamp() use
> > > either clamp_const() or clamp_nonconst() from above automagically.
> > > I'd prefer that.
> > 
> > Did you mean something like this?  No more clamp_val, just clamp and
> > clamp_t.  clamp_t forces all the types, clamp looks at the min and max
> > args, and if they are constants, uses the type of val instead.  If not
> > a constant, the strict typechecking is done.
> 
> > +#define clamp(val, min, max) ({				\
> > +	typeof(val) __val = (val);			\
> > +							\
> > +	if (__builtin_constant_p(min)) {		\
> > +		typeof(val) __min = (min);		\
> > +		__val = __val < __min ? __min: __val;	\
> > +	} else {					\
> > +		typeof(min) __min = (min);		\
> > +		(void) (&__val == &__min);		\
> > +		__val = __val < __min ? __min: __val;	\
> > +	}						\
> > +							\
> > +	if (__builtin_constant_p(max)) {		\
> > +		typeof(val) __max = (max);		\
> > +		__val > __max ? __max: __val;		\
> > +	} else {					\
> > +		typeof(max) __max = (max);		\
> > +		(void) (&__val == &__max);		\
> > +		__val > __max ? __max: __val;		\
> > +	} })
> 
> Yeah, something like that.
> Does returning of the value work over an indentation level, too?
> I dunno this detail of the language.
> But I'd prefer the following for readability anyway:
> 
> +       if (__builtin_constant_p(max)) {                \
> +               typeof(val) __max = (max);              \
> +               __val = __val > __max ? __max: __val;           \
> +       } else {                                        \
> +               typeof(max) __max = (max);              \
> +               (void) (&__val == &__max);              \
> +               __val = __val > __max ? __max: __val;           \
> +       }
> +	__val; })

Yeah, that is better. (and even works).

Harvey

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