linux-kernel - Re: [PATCH] include/log2.h: Fix rounddown_pow_of

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Date:	Mon, 14 Nov 2011 13:17:11 -0800 (PST)
From:	Andrei Warkentin <awarkentin@...are.com>
To:	Jesper Juhl <jj@...osbits.net>
Cc:	linux-kernel@...r.kernel.org, Andrei Warkentin <andreiw@...are.com>
Subject: Re: [PATCH] include/log2.h: Fix rounddown_pow_of_two(1)

----- Original Message -----
> From: "Jesper Juhl" <jj@...osbits.net>
> To: "Andrei Warkentin" <andreiw@...are.com>
> Cc: linux-kernel@...r.kernel.org
> Sent: Tuesday, November 8, 2011 2:57:27 PM
> Subject: Re: [PATCH] include/log2.h: Fix rounddown_pow_of_two(1)
> 
> On Tue, 8 Nov 2011, Andrei Warkentin wrote:
> 
> > 1 is a power of two, therefore rounddown_pow_of_two(1) should
> > return 1. It does
> > in case the argument is a variable but in case it's a constant it
> > behaves
> > wrong and returns 0. Probably nobody ever did it so this was never
> > noticed,
> > however net/drivers/vmxnet3 with latest GCC does and breaks on
> > unicpu systems.
> > 
> > Signed-off-by: Andrei Warkentin <andreiw@...are.com>
> > ---
> >  include/linux/log2.h |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/include/linux/log2.h b/include/linux/log2.h
> > index 25b8086..ccda848 100644
> > --- a/include/linux/log2.h
> > +++ b/include/linux/log2.h
> > @@ -185,7 +185,7 @@ unsigned long __rounddown_pow_of_two(unsigned
> > long n)
> >  #define rounddown_pow_of_two(n)			\
> >  (						\
> >  	__builtin_constant_p(n) ? (		\
> > -		(n == 1) ? 0 :			\
> > +		(n == 1) ? 1 :			\
> >  		(1UL << ilog2(n))) :		\
> >  	__rounddown_pow_of_two(n)		\
> >   )
> > 
> 
> For what it's worth; looks good to me.

Is that an Acked-by or a Reviewed-by?

Thanks,
A
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