linux-kernel - [RFC PATCH 1/6] kenrel.h: add ALIGN_OF_LAST

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Message-Id: <1332238884-6237-2-git-send-email-laijs@cn.fujitsu.com>
Date:	Tue, 20 Mar 2012 18:21:19 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Lai Jiangshan <laijs@...fujitsu.com>
Subject: [RFC PATCH 1/6] kenrel.h: add ALIGN_OF_LAST_BIT()

Get the biggest 2**y that x % (2**y) == 0 for the align value. 

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
 include/linux/kernel.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 5113462..2c439dc 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -44,6 +44,8 @@
 #define PTR_ALIGN(p, a)		((typeof(p))ALIGN((unsigned long)(p), (a)))
 #define IS_ALIGNED(x, a)		(((x) & ((typeof(x))(a) - 1)) == 0)
 
+#define ALIGN_OF_LAST_BIT(x)	((((x)^((x) - 1))>>1) + 1)
+
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
 
 /*
-- 
1.7.4.4

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