linux-kernel - Re: [PATCH 3/5] drivers/scsi: Use DIV_ROUND

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Date:	Mon, 3 Aug 2009 11:21:33 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Kurt Garloff <garloff@...e.de>, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 3/5] drivers/scsi: Use DIV_ROUND_CLOSEST

On Sun, 2 Aug 2009, Guennadi Liakhovetski wrote:

> On Sat, 1 Aug 2009, 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/scsi/tmscsim.c              |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > Diff --git a/drivers/scsi/tmscsim.c b/drivers/scsi/tmscsim.c
> > index 9a42734..7322f30 100644
> > --- a/drivers/scsi/tmscsim.c
> > +++ b/drivers/scsi/tmscsim.c
> > @@ -1125,7 +1125,8 @@ dc390_MsgIn_set_sync (struct dc390_acb* pACB, struct dc390_srb* pSRB)
> >      {
> >        if (! (bval & FAST_SCSI)) wval1++;
> >        printk (KERN_INFO "DC390: Target %i: Sync transfer %i.%1i MHz, Offset %i\n", pDCB->TargetID, 
> > -	      40/wval1, ((40%wval1)*10+wval1/2)/wval1, pDCB->SyncOffset & 0x0f);
> > +		40/wval1, DIV_ROUND_CLOSEST((40 % wval1) * 10, wval1),
> > +		pDCB->SyncOffset & 0x0f);
> >      }
> >    
> >    dc390_reprog (pACB, pDCB);
> 
> With all my respect to these scripted clean-up efforts, I am not sure this 
> really improves anything. I.e., I am not sure, that
> 
> 	z = DIV_ROUND_CLOSEST(x, y);
> 
> is better readable than
> 
> 	z = (x + y / 2) / y;
> 
> Besides, I do realise, that tmscsim.c indentation is dreadful (legacy 
> code...) but this patch changes it further from
> 
> 	printk("...",
> 	       x,
> 	       y);
> 
> to
> 
> 	printk("...",
> 		x,
> 		y);
> 
> which doesn't seem like an improvement to me either. That said, this does 
> compile, and I don't see why this shouldn't work, so, if we really want 
> this change here's the

I will adjust the spacing in the argument to printk.

julia
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