linux-kernel - [PATCH 2/2] bitops.h: add sign

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Date:	Thu, 15 Oct 2015 18:18:29 +0200
From:	Martin Kepplinger <martink@...teo.de>
To:	mingo@...nel.org, akpm@...ux-foundation.org, linux@...izon.com,
	linux@...musvillemoes.dk, maxime.coquelin@...com,
	dvlasenk@...hat.com, yury.norov@...il.com,
	torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org,
	Martin Kepplinger <martink@...teo.de>,
	Martin Kepplinger <martin.kepplinger@...obroma-systems.com>
Subject: [PATCH 2/2] bitops.h: add sign_extend64()

Months back, this was discussed, see https://lkml.org/lkml/2015/1/18/289
The result was the 64-bit version being "likely fine", "valuable" and
"correct". The discussion only fell asleep but since there are possible
users, let's add it.

Signed-off-by: Martin Kepplinger <martin.kepplinger@...obroma-systems.com>
---
 include/linux/bitops.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 2177c01..1672b74 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -173,6 +173,17 @@ 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)
-- 
2.1.4

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