From 636dd2b7def5c9c72551b51d4d516a65c269de08 Mon Sep 17 00:00:00 2001
From: Stephen Hemminger <shemminger@osdl.org>
Date: Wed, 11 Jan 2006 22:43:24 +0100
Subject: [PATCH] x86_64: fls in asm for x86_64
Use single instruction for find largest set bit on x86_64.
[Updated by Jan Beulich to fix wrong asm constraints in original
patch -AK]
Cc: jbeulich@novell.com
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
include/asm-x86_64/bitops.h | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/include/asm-x86_64/bitops.h b/include/asm-x86_64/bitops.h
index 3638ffff87..eb4df23e1e 100644
--- a/include/asm-x86_64/bitops.h
+++ b/include/asm-x86_64/bitops.h
@@ -396,6 +396,22 @@ static __inline__ int fls64(__u64 x)
return __fls(x) + 1;
}
+/**
+ * fls - find last bit set
+ * @x: the word to search
+ *
+ * This is defined the same way as ffs.
+ */
+static __inline__ int fls(int x)
+{
+ int r;
+
+ __asm__("bsrl %1,%0\n\t"
+ "cmovzl %2,%0"
+ : "=&r" (r) : "rm" (x), "rm" (-1));
+ return r+1;
+}
+
/**
* hweightN - returns the hamming weight of a N-bit word
* @x: the word to weigh
@@ -434,9 +450,6 @@ static __inline__ int fls64(__u64 x)
#define minix_find_first_zero_bit(addr,size) \
find_first_zero_bit((void*)addr,size)
-/* find last set bit */
-#define fls(x) generic_fls(x)
-
#endif /* __KERNEL__ */
#endif /* _X86_64_BITOPS_H */
--
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