linux-kernel - [ 51/55] tile: fix bug where fls(0) was not returning 0

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Date:	Sun, 27 May 2012 09:27:04 +0900
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Chris Metcalf <cmetcalf@...era.com>
Subject: [ 51/55] tile: fix bug where fls(0) was not returning 0

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Metcalf <cmetcalf@...era.com>

commit 9f1d62bed7f015d11b9164078b7fea433b474114 upstream.

This is because __builtin_clz(0) returns 64 for the "undefined" case
of 0, since the builtin just does a right-shift 32 and "clz" instruction.
So, use the alpha approach of casting to u32 and using __builtin_clzll().

Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/tile/include/asm/bitops.h |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/arch/tile/include/asm/bitops.h
+++ b/arch/tile/include/asm/bitops.h
@@ -77,6 +77,11 @@ static inline int ffs(int x)
 	return __builtin_ffs(x);
 }
 
+static inline int fls64(__u64 w)
+{
+	return (sizeof(__u64) * 8) - __builtin_clzll(w);
+}
+
 /**
  * fls - find last set bit in word
  * @x: the word to search
@@ -90,12 +95,7 @@ static inline int ffs(int x)
  */
 static inline int fls(int x)
 {
-	return (sizeof(int) * 8) - __builtin_clz(x);
-}
-
-static inline int fls64(__u64 w)
-{
-	return (sizeof(__u64) * 8) - __builtin_clzll(w);
+	return fls64((unsigned int) x);
 }
 
 static inline unsigned int __arch_hweight32(unsigned int w)


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