From: Oleg Verych <olecom@flower.upol.cz>
To: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@ftp.linux.org.uk>,
akpm@linux-foundation.org, benh@kernel.crashing.org,
linux-kernel@vger.kernel.org, hpa@zytor.com,
johannes@sipsolutions.net
Subject: ALIGN via ilog2 without gccisms (Re: [PATCH] Fix get_order())
Date: Wed, 7 Mar 2007 17:02:53 +0100 [thread overview]
Message-ID: <E1HOybN-00031m-6M@flower> (raw)
In-Reply-To: <8543.1173267786@redhat.com>
> From: David Howells
> Newsgroups: gmane.linux.kernel
> Subject: Re: [PATCH] Fix get_order()
> Date: Wed, 07 Mar 2007 11:43:06 +0000
>
[]
> Various archs (including i386, x86_64, powerpc and frv) have instructions that
> can be used to calculate integer log2(N).
>
Probably it can be used to get rid of gccisms and "type fluff" due to
bitwise arithmetics in ALIGN?
Here:
#define ALIGN(x,a) __ALIGN_MASK(x,(typeof(x))(a)-1)
#define __ALIGN_MASK(x,mask) (((x)+(mask))&~(mask))
like that:
#define ALIGN(x,y) __ALIGN_MASK(x,ilog2(y))
#define __ALIGN_MASK(x,bits) (((((x) >> (bits)) << 1) + 2) << (bits - 1))
Note side effect, that this one always yields even result. Maybe this is
good, due to avoidance of misaligned access.
____
next prev parent reply other threads:[~2007-03-07 15:53 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-06 17:39 [PATCH] Fix get_order() David Howells
2007-03-06 17:58 ` H. Peter Anvin
2007-03-06 18:21 ` David Howells
2007-03-06 18:41 ` Linus Torvalds
2007-03-06 18:51 ` David Howells
2007-03-07 3:28 ` Linus Torvalds
2007-03-07 11:43 ` David Howells
2007-03-07 16:02 ` Oleg Verych [this message]
2007-03-07 16:38 ` ALIGN via ilog2 without gccisms (Re: [PATCH] Fix get_order()) Linus Torvalds
2007-03-07 17:24 ` Oleg Verych
2007-03-07 18:05 ` Linus Torvalds
2007-03-09 23:13 ` ALIGN " Oleg Verych
2007-03-09 23:15 ` Linus Torvalds
2007-03-10 0:31 ` Oleg Verych
2007-03-10 8:01 ` ALIGN Oleg Verych
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