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

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Message-Id: <20070425082028.8ece3094.randy.dunlap@oracle.com>
Date:	Wed, 25 Apr 2007 08:20:28 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Richard Knutsson <ricknu-0@...dent.ltu.se>
Cc:	Jiri Bohac <jbohac@...e.cz>, akpm@...l.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] fix abs() macro to work with types wider than int

On Fri, 20 Apr 2007 14:44:38 +0200 Richard Knutsson wrote:

> Randy Dunlap wrote:
> > On Thu, 19 Apr 2007 11:23:39 +0200 Jiri Bohac wrote:
> >
> >   
> >> Hi,
> >>
> >> is there any reason to use an explicit int instead of a typeof in
> >> the abs() macro? The current implementation will return bogus
> >> results when used with longs.
> >>     
> >
> > 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.

> >> How about changing the int to a typeof like this?:
> >>
> >>
> >>
> >> Fix the abs() macro to work with wider types than int.
> >>
> >> Signed-off-by: Jiri Bohac <jbohac@...e.cz>
> >>
> >> --- linux-2.6.21-rc5.orig/include/linux/kernel.h
> >> +++ linux-2.6.21-rc5/include/linux/kernel.h
> >> @@ -89,7 +89,7 @@ extern int cond_resched(void);
> >>  #define might_sleep_if(cond) do { if (cond) might_sleep(); } while (0)
> >>  
> >>  #define abs(x) ({				\
> >> -		int __x = (x);			\
> >> +		typeof(x) __x = (x);			\
> >>  		(__x < 0) ? -__x : __x;		\
> >>  	})


---
~Randy
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