linux-kernel - [PATCH 1/7] FRV: Fix fls() to handle bit 31 being set correctly [try #3]

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Message-Id: <20060913183522.22109.10565.stgit@warthog.cambridge.redhat.com>
Date:	Wed, 13 Sep 2006 19:35:22 +0100
From:	David Howells <dhowells@...hat.com>
To:	torvalds@...l.org, akpm@...l.org
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	dhowells@...hat.com
Subject: [PATCH 1/7] FRV: Fix fls() to handle bit 31 being set correctly [try #3]

From: David Howells <dhowells@...hat.com>

Fix FRV fls() to handle bit 31 being set correctly (it should return 32 not 0).

Signed-Off-By: David Howells <dhowells@...hat.com>
---

 include/asm-frv/bitops.h |   21 +++++++++++++++++----
 1 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/asm-frv/bitops.h b/include/asm-frv/bitops.h
index 980ae1b..97fb746 100644
--- a/include/asm-frv/bitops.h
+++ b/include/asm-frv/bitops.h
@@ -161,16 +161,29 @@ #include <asm-generic/bitops/ffs.h>
 #include <asm-generic/bitops/__ffs.h>
 #include <asm-generic/bitops/find.h>
 
-/*
- * fls: find last bit set.
+/**
+ * fls - find last bit set
+ * @x: the word to search
+ *
+ * This is defined the same way as ffs:
+ * - return 32..1 to indicate bit 31..0 most significant bit set
+ * - return 0 to indicate no bits set
  */
 #define fls(x)						\
 ({							\
 	int bit;					\
 							\
-	asm("scan %1,gr0,%0" : "=r"(bit) : "r"(x));	\
+	asm("	subcc	%1,gr0,gr0,icc0		\n"	\
+	    "	ckne	icc0,cc4		\n"	\
+	    "	cscan.p	%1,gr0,%0	,cc4,#1	\n"	\
+	    "	csub	%0,%0,%0	,cc4,#0	\n"	\
+	    "   csub    %2,%0,%0	,cc4,#1	\n"	\
+	    : "=&r"(bit)				\
+	    : "r"(x), "r"(32)				\
+	    : "icc0", "cc4"				\
+	    );						\
 							\
-	bit ? 33 - bit : bit;				\
+	bit;						\
 })
 
 #include <asm-generic/bitops/fls64.h>
-
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