linux-kernel - Re: [PATCH 2/5] drivers/media/video/uvc: Use DIV_ROUND

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Date:	Sun, 2 Aug 2009 08:20:04 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Laurent Pinchart <laurent.pinchart@...net.be>
Cc:	linux-media@...r.kernel.org, linux-uvc-devel@...ts.berlios.de,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 2/5] drivers/media/video/uvc: Use DIV_ROUND_CLOSEST

On Sat, 1 Aug 2009, Laurent Pinchart wrote:

> On Saturday 01 August 2009 21:49:04 Julia Lawall wrote:
> > From: Julia Lawall <julia@...u.dk>
> >
> > The kernel.h macro DIV_ROUND_CLOSEST performs the computation (x + d/2)/d
> > but is perhaps more readable.
> >
> > The semantic patch that makes this change is as follows:
> > (http://www.emn.fr/x-info/coccinelle/)
> >
> > // <smpl>
> > @haskernel@
> > @@
> >
> > #include <linux/kernel.h>
> >
> > @depends on haskernel@
> > expression x,__divisor;
> > @@
> >
> > - (((x) + ((__divisor) / 2)) / (__divisor))
> > + DIV_ROUND_CLOSEST(x,__divisor)
> > // </smpl>
> >
> > Signed-off-by: Julia Lawall <julia@...u.dk>
> >
> > ---
> >  drivers/media/video/uvc/uvc_v4l2.c  |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/media/video/uvc/uvc_v4l2.c
> > b/drivers/media/video/uvc/uvc_v4l2.c index 87cb9cc..6edaaf6 100644
> > --- a/drivers/media/video/uvc/uvc_v4l2.c
> > +++ b/drivers/media/video/uvc/uvc_v4l2.c
> > @@ -95,7 +95,7 @@ static __u32 uvc_try_frame_interval(struct uvc_frame
> > *frame, __u32 interval) const __u32 max = frame->dwFrameInterval[1];
> >  		const __u32 step = frame->dwFrameInterval[2];
> >
> > -		interval = min + (interval - min + step/2) / step * step;
> > +		interval = min + DIV_ROUND_CLOSEST(interval-min, step) * step;
> >  		if (interval > max)
> >  			interval = max;
> >  	}
> 
> The purpose of the above code is to clamp the interval value to the [min, max] 
> range at round it to the closest multiple of step. Other drivers might need 
> similar code. Do you think it might be useful to introduce a clamp_step macro 
> for this ?

I tried searching for the following:

@@
expression interval, min, max, step, E;
@@

* interval = min + (interval - min + step/2) / step * step;
  ... when != interval = E
* if (interval > max)
  { ...
     interval = max;
  ... }

@@
expression interval, min, max, step, E;
@@

* interval = min + DIV_ROUND_CLOSEST(interval-min, step) * step;
  ... when != interval = E
* if (interval > max) { ...
     interval = max;
  ... }

and the only occurrence I found was the code above.  Perhaps there is some 
other way in which the pattern would appear?

julia
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