linux-kernel - Re: ALIGN (Re: [PATCH] Fix get

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Date:	Sat, 10 Mar 2007 00:13:34 +0100
From:	Oleg Verych <olecom@...wer.upol.cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Howells <dhowells@...hat.com>,
	Al Viro <viro@....linux.org.uk>, akpm@...ux-foundation.org,
	benh@...nel.crashing.org, linux-kernel@...r.kernel.org,
	hpa@...or.com, johannes@...solutions.net
Subject: Re: ALIGN (Re: [PATCH] Fix get_order())

On Wed, Mar 07, 2007 at 08:38:27AM -0800, Linus Torvalds wrote:
> 
> 
> On Wed, 7 Mar 2007, Oleg Verych wrote:
> >
> > Probably it can be used to get rid of gccisms and "type fluff" due to
> > bitwise arithmetics in ALIGN?
> 
> Hell no.
> 
> The typeof is there to make sure we have the right type, and it's simple.
> 
> The current ALIGN() macro is efficient as hell (generating just a simple 
> mask+add). Turning it into some kind of horrible thing that uses ilog2() 
> would be a total mistake.

OTOH, if i would write it this way

#define BALIGN(x,bits)      ((((x) >> (bits)) + 1) << (bits))

that would give more convenient way of expessing alignment (values of
what are most widely used, i.e powers of two) without log2(:)
requirement, no?

arch/powerpc/mm/hugetlbpage.c:                  addr = ALIGN(addr+1,1UL<<HTLB_AREA_SHIFT);
arch/powerpc/mm/hugetlbpage.c:                  addr = ALIGN(addr+1,1<<SID_SHIFT);

But it's not conventional, of course, and name is ugly.
____
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