netdev - Re: [PATCH 2/4] dsmark: get rid of trivial function

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Date:	Mon, 21 Jan 2008 10:39:21 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Patrick McHardy <kaber@...sh.net>,
	Stephen Hemminger <shemminger@...tta.com>
cc:	David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/4] dsmark: get rid of trivial function

On Mon, 21 Jan 2008, Patrick McHardy wrote:

> Stephen Hemminger wrote:
> > Replace loop in dsmark_valid_indices with equivalent bit math.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> > 
> > --- a/net/sched/sch_dsmark.c	2008-01-20 13:07:58.000000000 -0800
> > +++ b/net/sched/sch_dsmark.c	2008-01-20 13:22:54.000000000 -0800
> > @@ -45,13 +45,8 @@ struct dsmark_qdisc_data {
> >  
> >  static inline int dsmark_valid_indices(u16 indices)
> >  {
> > -	while (indices != 1) {
> > -		if (indices & 1)
> > -			return 0;
> > -		indices >>= 1;
> > -	}
> > -
> > -	return 1;
> > +	/* Must have only one bit set */
> > +	return (indices & (indices - 1)) == 0;

Isn't there some magic under include/linux to do that btw, I suppose 
that if the caller side zero check is pushed down there too, the
is_power_of_2() is 100% match? :-) 

> hweight seems easier to understand, it took me a bit
> to realize that the comment matches the code :)

In addition, the original seems infinite loop with zero indices given
but luckily that was checked at the caller site already...


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