Message-ID: <4B5A05A1.3040901@zytor.com>
Date: Fri, 22 Jan 2010 12:08:01 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Joe Perches <joe@perches.com>
CC: Christoph Lameter <cl@linux-foundation.org>,
       Yinghai Lu <yinghai@kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Jesse Barnes <jbarnes@virtuousgeek.org>, linux-kernel@vger.kernel.org,
       linux-pci@vger.kernel.org
Subject: Re: [PATCH 24/38] move round_up/down to kernel.h
References: <1264152287-13866-1-git-send-email-yinghai@kernel.org>	 <1264152287-13866-25-git-send-email-yinghai@kernel.org>	 <alpine.DEB.2.00.1001220851210.2704@router.home> <1264188512.32383.118.camel@Joe-Laptop.home>
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On 01/22/2010 11:28 AM, Joe Perches wrote:
> On Fri, 2010-01-22 at 08:52 -0600, Christoph Lameter wrote:
>> On Fri, 22 Jan 2010, Yinghai Lu wrote:
>>> +#define __round_mask(x,y) ((__typeof__(x))((y)-1))
>>> +#define round_up(x,y) ((((x)-1) | __round_mask(x,y))+1)
>>> +#define round_down(x,y) ((x) & ~__round_mask(x,y))
>> s/round/round_power2/
> 
> s/round/round_power_of_2/
> BUILD_BUG_ON_NOT_POWER_OF_2
> 

Uh... the whole reason why the classical rounding functions don't work
is that we're using it with non-constants, and therefore the compiler
doesn't know that we're restricted to powers of two (and therefore it
will generate divides.)

	-hpa
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