linux-kernel - [PATCH] bitops.h: correctly handle rol32 with 0 byte shift

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Date:	Thu,  3 Dec 2015 17:02:45 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	torvalds@...ux-foundation.org
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	Sasha Levin <sasha.levin@...cle.com>
Subject: [PATCH] bitops.h: correctly handle rol32 with 0 byte shift

rol on a 32 bit integer with a shift of 32 or more is undefined and the
result is arch-dependent. Avoid this by handling the trivial case of
roling by 0 correctly.

Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
---
 include/linux/bitops.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 2b8ed12..7047a06 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -107,7 +107,7 @@ static inline __u64 ror64(__u64 word, unsigned int shift)
  */
 static inline __u32 rol32(__u32 word, unsigned int shift)
 {
-	return (word << shift) | (word >> (32 - shift));
+	return shift ? (word << shift) | (word >> (32 - shift)) : word;
 }
 
 /**
-- 
1.7.10.4

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