From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wu Fengguang <fengguang.wu@intel.com>
Subject: [PATCH 2/5] bitops: compile time optimization for hweight_long(CONSTANT)
Date: Sat, 30 Jan 2010 17:45:17 +0800
Message-ID: <20100130094957.692671259@intel.com>
References: <20100130094515.475881280@intel.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Jamie Lokier <jamie@shareable.org>,
	Roland Dreier <rdreier@cisco.com>
To: Andrew Morton <akpm@linux-foundation.org>
Return-path: <linux-kernel-owner+glk-linux-kernel-3=40m.gmane.org-S1753477Ab0A3JyE@vger.kernel.org>
cc: Al Viro <viro@ZenIV.linux.org.uk>
cc: <linux-fsdevel@vger.kernel.org>
Content-Disposition: inline; filename=constant-hweight32.patch
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

This allows use of hweight_long() in BUILD_BUG_ON().
Suggested by Jamie.

CC: Jamie Lokier <jamie@shareable.org>
CC: Roland Dreier <rdreier@cisco.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 include/linux/bitops.h |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- linux-mm.orig/include/linux/bitops.h	2009-07-20 20:10:19.000000000 +0800
+++ linux-mm/include/linux/bitops.h	2010-01-30 17:41:15.000000000 +0800
@@ -40,10 +40,14 @@ static __inline__ int get_count_order(un
 	return order;
 }
 
-static inline unsigned long hweight_long(unsigned long w)
-{
-	return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
-}
+#define hweight_long(x)				\
+(						\
+	__builtin_constant_p(x) ?		\
+		__builtin_popcountl(x) :	\
+		(sizeof(x) <= 4 ?		\
+			 hweight32(x) :		\
+			 hweight64(x))		\
+)
 
 /**
  * rol32 - rotate a 32-bit value left