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

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Message-ID: <Pine.LNX.4.61.0704251612090.27302@chaos.analogic.com>
Date:	Wed, 25 Apr 2007 16:30:29 -0400
From:	"linux-os \(Dick Johnson\)" <linux-os@...logic.com>
To:	"Andreas Schwab" <schwab@...e.de>
Cc:	"John Anthony Kazos Jr." <jakj@...-k-j.com>,
	"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, Andreas Schwab wrote:

> "linux-os (Dick Johnson)" <linux-os@...logic.com> writes:
>
>> I think this works, regardless of the length of the integers:
>>
>> #define abs(x) (((x)<0)?-(x):(x))
>
> But it evaluates its argument more than once.
>
> Andreas.
>

Sure. Macros do that. If that's not okay, then you need either
a temporary variable or a function. The original query was for
a macro. Any macro that tests something then returns a value
based upon the test is going to have that problem. Any attempt
to just AND off a sign bit is going to have width problems. You
can't have your cake and eat it too. Even whacking off the sign-
bit may fail because there may be two variable accesses which could
mean two function calls, destroying the logic.

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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