[PATCH 2/5] bitops: compile time optimization for hweight_long(CONSTANT)

[Wu Fengguang]

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

CC: Jamie Lokier <jamie@xxxxxxxxxxxxx>
CC: Roland Dreier <rdreier@xxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 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


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