linux-kernel - [PATCH] bitops.h: add sign

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Message-Id: <1418666055-16657-1-git-send-email-martink@posteo.de>
Date:	Mon, 15 Dec 2014 18:54:15 +0100
From:	Martin Kepplinger <martink@...teo.de>
To:	peterz@...radead.org
Cc:	mingo@...nel.org, tytso@....edu, linux-kernel@...r.kernel.org,
	Martin Kepplinger <martink@...teo.de>
Subject: [PATCH] bitops.h: add sign_extend64() function

This adds sign_exten64 to sign extend any signed value shorter than 64 bits
to a s64.

Signed-off-by: Martin Kepplinger <martink@...teo.de>
Suggested-by: Christoph Muellner <christoph.muellner@...obroma-systems.com>
---
Without looking for it's users yet: This applies on top of it's 8 and 16 bit
friends.

This reminded me of giving credit for the initial idea. At least in one patch
I'd like to have him mentioned.


 include/linux/bitops.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 70190f4..9c31680 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -193,6 +193,17 @@ static inline __s32 sign_extend32(__u32 value, int index)
 	return (__s32)(value << shift) >> shift;
 }
 
+/**
+ * sign_extend64 - sign extend a 64-bit value using specified bit as sign-bit
+ * @value: value to sign extend
+ * @index: 0 based bit index (0<=index<64) to sign bit
+ */
+static inline __s64 sign_extend64(__u64 value, int index)
+{
+	__u8 shift = 63 - index;
+	return (__s64)(value << shift) >> shift;
+}
+
 static inline unsigned fls_long(unsigned long l)
 {
 	if (sizeof(l) == 4)
-- 
2.1.3

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