[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>
diff --git a/include/asm-x86_64/bitops.h b/include/asm-x86_64/bitops.h
index 3638fff..eb4df23 100644
--- a/include/asm-x86_64/bitops.h
+++ b/include/asm-x86_64/bitops.h
@@ -397,6 +397,22 @@
}
/**
+ * 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 @@
#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 */