linux-kernel - Re: [RFC][PATCH] fix abs() macro to work with types wider than int

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Message-ID: <Pine.LNX.4.61.0704251418010.26778@chaos.analogic.com>
Date:	Wed, 25 Apr 2007 14:24:12 -0400
From:	"linux-os \(Dick Johnson\)" <linux-os@...logic.com>
To:	"John Anthony Kazos Jr." <jakj@...-k-j.com>
Cc:	"Randy Dunlap" <randy.dunlap@...cle.com>,
	"Richard Knutsson" <ricknu-0@...dent.ltu.se>,
	"Jiri Bohac" <jbohac@...e.cz>, <akpm@...l.org>,
	"Linux kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] fix abs() macro to work with types wider than int

On Wed, 25 Apr 2007, John Anthony Kazos Jr. wrote:

>>>> I think it's like it is just to be consistent with abs() in C,
>>>> which also contains labs() and llabs().
>>>>
>>> We actually had labs() before (few months ago), but since it was not
>>> used, and if it would it seemed better to just fix abs(), it was
>>> removed. So I think this is the appropriate way to go.
>>
>> Sounds like when someone actually needs labs() or llabs()
>> they can submit a patch for however they would like to use it.
>
> However they would like to use *abs()? What different ways are possible to
> take the arithmetic absolute value? I see record of many cases where
> dozens of authors have macros that then get collapsed to include files. So
> why not avoid that annoyance this time and -start- with it in the include
> files?
>
> Can there even be any reason beyond unnecessary pedantics to have
> [l[l]]abs?

Isn't any macro that looks for "< 0" insensitive to the word length? I think 
it's only when people try tricks with "sign-bits," that they get into trouble.
I think this works, regardless of the length of the integers:

#define abs(x) (((x)<0)?-(x):(x))

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.62 BogoMips).
New book: http://www.AbominableFirebug.com/
_
..

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