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

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Date:	Sat, 1 Aug 2009 22:23:51 +0200
From:	Laurent Pinchart <laurent.pinchart@...net.be>
To:	Julia Lawall <julia@...u.dk>
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 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 ?

If not,

Acked-by: Laurent Pinchart <laurent.pinchart@...net.be>

Regards,

Laurent Pinchart

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