linux-kernel - Re: [PATCH 01/10] Add macros similar to min/max/min_t/max

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Date:	Fri, 14 Mar 2008 10:06:48 -0700
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] Add macros similar to min/max/min_t/max_t.

On Fri, 2008-03-14 at 09:49 -0700, Randy Dunlap wrote:
> Harvey Harrison wrote:
> > On Fri, 2008-03-14 at 09:34 -0700, Randy Dunlap wrote:
> >> On Thu, 13 Mar 2008 22:18:45 -0700 Harvey Harrison wrote:
> > 
> >> Where is some blurb/comment about what "clamp" means/does?
> >> min/max are well understood, but clamp?  Is that a shop tool?
> >> I think I have a few out in my garage.
> > Sure, I'll do that..does kernel-doc actually work for macros?
> 
> Yes, it does.
> 

OK, here's what I've come up with:

/**
 * clamp - return a value clamped to a given range with strict typechecking
 * @val: current value
 * @min: minimum allowable value
 * @max: maximum allowable value
 *
 * This macro does strict typechecking of min/max to make sure they of the
 * same type as val.  See the unnecessary pointer comparisons.
 */
#define clamp(val, min, max) ({			\
	typeof(val) __val = (val);		\
	typeof(min) __min = (min);		\
	typeof(max) __max = (max);		\
	(void) (&__val == &__min);		\
	(void) (&__val == &__max);		\
	__val = __val < __min ? __min: __val;	\
	__val > __max ? __max: __val; })

/**
 * clamp_t - return a value clamped to a given range using a given type
 * @type: the type of variable to use
 * @val: current value
 * @min: minimum allowable value
 * @max: maximum allowable value
 *
 * This macro does no typechecking and uses temporary variables of type
 * 'type' to make all the comparisons.
 */
#define clamp_t(type, val, min, max) ({		\
	type __val = (val);			\
	type __min = (min);			\
	type __max = (max);			\
	__val = __val < __min ? __min: __val;	\
	__val > __max ? __max: __val; })

/**
 * clamp_val - return a value clamped to a given range using val's type
 * @val: current value
 * @min: minimum allowable value
 * @max: maximum allowable value
 *
 * This macro does no typechecking and uses temporary variables of whatever
 * type the input argument 'val' is.  This is useful when val is an unisgned
 * type and min and max are literals that will otherwise be assigned a signed
 * integer type.
 */
#define clamp_val(val, min, max) ({		\
	typeof(val) __val = (val);		\
	typeof(val) __min = (min);		\
	typeof(val) __max = (max);		\
	__val = __val < __min ? __min: __val;	\
	__val > __max ? __max: __val; })

Comments?  Please let me know if I got the kerneldoc format right.

Harvey

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