linux-kernel - Re: [PATCH] Make shr to divide by power of 2 (resend)

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Message-ID: <alpine.LFD.2.00.0908150947260.14440@localhost>
Date:	Sat, 15 Aug 2009 09:49:15 -0400 (EDT)
From:	"Robert P. J. Day" <rpjday@...shcourse.ca>
To:	Jiri Slaby <jirislaby@...il.com>
cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Make shr to divide by power of 2 (resend)

On Sat, 15 Aug 2009, Jiri Slaby wrote:

> On 08/15/2009 03:43 PM, Sergey Senozhatsky wrote:
> > Make an arithmetic right shift to divide by power of 2.
>
> Why? Is out there a compiler not doing that?
>
> Seems like it should be rather converted to DIV_ROUND_UP.
>
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> > ---
> > diff --git a/drivers/video/console/bitblit.c b/drivers/video/console/bitblit.c
> > index 69864b1..b816151 100644
> > --- a/drivers/video/console/bitblit.c
> > +++ b/drivers/video/console/bitblit.c
> > @@ -144,7 +144,7 @@ static void bit_putcs(struct vc_data *vc, struct fb_info *info,
> >  		      int fg, int bg)
> >  {
> >  	struct fb_image image;
> > -	u32 width = (vc->vc_font.width + 7)/8;
> > +	u32 width = (vc->vc_font.width + 7) >> 3;
> >  	u32 cellsize = width * vc->vc_font.height;
> >  	u32 maxcnt = info->pixmap.size/cellsize;
> >  	u32 scan_align = info->pixmap.scan_align - 1;

  it does seem like a DIV_ROUND_UP would be better but perhaps another
solution would be to define a meaningful macro name for that
operation.  if that conversion is going to be done regularly, a macro
with an informative name might be in order.  if it's a one-shot
operation, though, not much point.

rday
--

========================================================================
Robert P. J. Day                               Waterloo, Ontario, CANADA

        Linux Consulting, Training and Annoying Kernel Pedantry.

Web page:                                          http://crashcourse.ca
Twitter:                                       http://twitter.com/rpjday
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