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

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Date:	Thu, 10 May 2007 07:52:57 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Satyam Sharma <satyam.sharma@...il.com>
Cc:	"Pallipadi\, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [PATCH -mm] timer: parenthesis fix in tbase_get_deferrable() etc.

On Wed, May 09, 2007 at 11:59:39PM +0530, Satyam Sharma wrote:
> On 5/9/07, Pallipadi, Venkatesh <venkatesh.pallipadi@...el.com> wrote:
> >
> >>-----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:
...
> >>> >  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?

I am sorry, too - for my "logic". It seems it's all correct!
(Except, I don't know what's going here...)

> >
> >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.
> 
> But that is not what the original code is doing. If you wanted to
> typecast "base" to "a 32 bit value" then you should've used u32
> instead.
> 
> Anyway, if you originally intended to actually typecast "base" to
> unsigned int, then you could do that directly without typecasting it
> first to unsigned long (unnecessarily) and then to unsigned int. Of
> course, if your system implements a pointer as something bigger than
> unsigned int (which is what you eventually convert "base" to), then
> you're screwed anyway and the intermediate typecast to unsigned long
> doesn't buy you anything at all.
> 
> The other 3 changes in this patch were clearly meaningless, though.
> 

	((unsigned int)(unsigned long)base ...
	((tvec_base_t *)((unsigned long)base ...
	((tvec_base_t *)((unsigned long)(timer->base) ...
	(tvec_base_t *)((unsigned long)(new_base) ...

Yes, if you don't count reading this one close each other, they are
clearly meaningles.

Regards,
Jarek P.
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