linux-kernel - [PATCH] bitops: Provide generic sign_extend function (moving it out from wireless code)

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Date:	Fri, 27 Aug 2010 12:16:51 +0200
From:	Andreas Herrmann <herrmann.der.user@...glemail.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Borislav Petkov <borislav.petkov@....com>,
	Zhu Yi <yi.zhu@...el.com>,
	"Luis R. Rodriguez" <lrodriguez@...eros.com>
Subject: [PATCH] bitops: Provide generic sign_extend function (moving it
 out from wireless code)

From: Andreas Herrmann <andreas.herrmann3@....com>

Provide a common function to sign extend a value.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>
---
 drivers/net/wireless/ath/ath5k/phy.c    |    6 ------
 drivers/net/wireless/ath/ath9k/hw.h     |    6 ------
 drivers/net/wireless/iwlwifi/iwl-4965.c |   16 ----------------
 include/linux/bitops.h                  |   11 +++++++++++
 4 files changed, 11 insertions(+), 28 deletions(-)

Recently I needed to sign extend some register values for further
computation. I also stumbled over two functions in wireless code
which do the same (in different ways).

Thus I wonder whether a generic function should be provided for this.

Below patch (against tip/master) provides the iwl-4965-variant of that
function in bitops.h I am not sure whether that's the right place to
add this function.  What do you think? Or is it a dumb idea anyway?


Thanks,
Andreas

diff --git a/drivers/net/wireless/ath/ath5k/phy.c b/drivers/net/wireless/ath/ath5k/phy.c
index 6284c38..9e6f551 100644
--- a/drivers/net/wireless/ath/ath5k/phy.c
+++ b/drivers/net/wireless/ath/ath5k/phy.c
@@ -1101,12 +1101,6 @@ int ath5k_hw_channel(struct ath5k_hw *ah, struct ieee80211_channel *channel)
   PHY calibration
 \*****************/
 
-static int sign_extend(int val, const int nbits)
-{
-	int order = BIT(nbits-1);
-	return (val ^ order) - order;
-}
-
 static s32 ath5k_hw_read_measured_noise_floor(struct ath5k_hw *ah)
 {
 	s32 val;
diff --git a/drivers/net/wireless/ath/ath9k/hw.h b/drivers/net/wireless/ath/ath9k/hw.h
index 399f7c1..5dad02f 100644
--- a/drivers/net/wireless/ath/ath9k/hw.h
+++ b/drivers/net/wireless/ath/ath9k/hw.h
@@ -858,12 +858,6 @@ static inline struct ath_hw_ops *ath9k_hw_ops(struct ath_hw *ah)
 	return &ah->ops;
 }
 
-static inline int sign_extend(int val, const int nbits)
-{
-	int order = BIT(nbits-1);
-	return (val ^ order) - order;
-}
-
 /* Initialization, Detach, Reset */
 const char *ath9k_hw_probe(u16 vendorid, u16 devid);
 void ath9k_hw_deinit(struct ath_hw *ah);
diff --git a/drivers/net/wireless/iwlwifi/iwl-4965.c b/drivers/net/wireless/iwlwifi/iwl-4965.c
index d92b729..9a53dee 100644
--- a/drivers/net/wireless/iwlwifi/iwl-4965.c
+++ b/drivers/net/wireless/iwlwifi/iwl-4965.c
@@ -1551,22 +1551,6 @@ static void iwl4965_txq_update_byte_cnt_tbl(struct iwl_priv *priv,
 }
 
 /**
- * sign_extend - Sign extend a value using specified bit as sign-bit
- *
- * Example: sign_extend(9, 3) would return -7 as bit3 of 1001b is 1
- * and bit0..2 is 001b which when sign extended to 1111111111111001b is -7.
- *
- * @param oper value to sign extend
- * @param index 0 based bit index (0<=index<32) to sign bit
- */
-static s32 sign_extend(u32 oper, int index)
-{
-	u8 shift = 31 - index;
-
-	return (s32)(oper << shift) >> shift;
-}
-
-/**
  * iwl4965_hw_get_temperature - return the calibrated temperature (in Kelvin)
  * @statistics: Provides the temperature reading from the uCode
  *
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index fc68053..618f69e 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -109,6 +109,17 @@ static inline __u8 ror8(__u8 word, unsigned int shift)
 	return (word >> shift) | (word << (8 - shift));
 }
 
+/**
+ * sign_extend - Sign extend a value using specified bit as sign-bit
+ * @value: value to sign extend
+ * @index: 0 based bit index (0<=index<32) to sign bit
+ */
+static inline __s32 sign_extend(__u32 value, int index)
+{
+	__u8 shift = 31 - index;
+	return (__s32)(value << shift) >> shift;
+}
+
 static inline unsigned fls_long(unsigned long l)
 {
 	if (sizeof(l) == 4)
-- 
1.6.4.4

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