linux-kernel - RE: [PATCH -mm] timer: parenthesis fix in tbase_get

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Message-ID: <653FFBB4508B9042B5D43DC9E18836F55DF9FD@scsmsx415.amr.corp.intel.com>
Date:	Wed, 9 May 2007 08:59:27 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	"Jarek Poplawski" <jarkao2@...pl>,
	"Andrew Morton" <akpm@...ux-foundation.org>
CC:	<linux-kernel@...r.kernel.org>, "Oleg Nesterov" <oleg@...sign.ru>
Subject: RE: [PATCH -mm] timer: parenthesis fix in tbase_get_deferrable() etc.


>-----Original Message-----
>From: Jarek Poplawski [mailto:jarkao2@...pl] 
>Sent: Tuesday, May 08, 2007 10:32 PM
>To: Andrew Morton
>Cc: Pallipadi, Venkatesh; linux-kernel@...r.kernel.org; Oleg Nesterov
>Subject: Re: [PATCH -mm] timer: parenthesis fix in 
>tbase_get_deferrable() etc.
>
>On Tue, May 08, 2007 at 04:33:58PM -0700, Andrew Morton wrote:
>> On Tue, 8 May 2007 12:33:48 +0200
>> Jarek Poplawski <jarkao2@...pl> wrote:
>> 
>> > 
>> > Signed-off-by: Jarek Poplawski <jarkao2@...pl>
>> > 
>> > ---
>> > 
>> > diff -Nurp 2.6.21-mm1-/kernel/timer.c 2.6.21-mm1/kernel/timer.c
>> > --- 2.6.21-mm1-/kernel/timer.c	2007-05-08 
>11:54:48.000000000 +0200
>> > +++ 2.6.21-mm1/kernel/timer.c	2007-05-08 
>12:05:11.000000000 +0200
>> > @@ -92,24 +92,24 @@ static DEFINE_PER_CPU(tvec_base_t *, tve
>> >  /* Functions below help us manage 'deferrable' flag */
>> >  static inline unsigned int tbase_get_deferrable(tvec_base_t *base)
>> >  {
>> > -	return ((unsigned int)(unsigned long)base & 
>TBASE_DEFERRABLE_FLAG);
>> > +	return (unsigned int)((unsigned long)base & 
>TBASE_DEFERRABLE_FLAG);
>> >  }
>...
>> The change makes sense, but does it actually "fix" anything?
>> 
>
>Yes - this first place fixes logical error, so it's a sin
>- even if not punishable in practice. (It's also unnecessary
>test for long to int conversion.)
>

I am sorry, I don't understand. What is the logical error in the first
one?

Actually, your change makes it different from what was originally
indended.
Original intention was to type convert base to a 32 bit value and
bitwise& with FLAG. Even though compiler may optimize both the above to
same code, I don't see what is the error.

Thanks,
Venki 
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