[PATCH] x86: fls() in asm

There is a single instruction on i386 to find largest set bit; so it makes
sense to use it (like we use bfs for ffs()).

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 17 insertions, 5 deletions

diff --git a/include/asm-i386/bitops.h b/include/asm-i386/bitops.h
index 26eb9811712f..65679aca4b22 100644
--- a/include/asm-i386/bitops.h
+++ b/include/asm-i386/bitops.h
@@ -367,11 +367,6 @@ static inline unsigned long ffz(unsigned long word)
         return word;
 }
 
-/*
- * fls: find last bit set.
- */
-
-#define fls(x) generic_fls(x)
 #define fls64(x)   generic_fls64(x)
 
 #ifdef __KERNEL__
@@ -415,6 +410,23 @@ static inline int ffs(int x)
 }
 
 /**
+ * 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"
+                "jnz 1f\n\t"
+                "movl $-1,%0\n"
+                "1:" : "=r" (r) : "rm" (x));
+        return r+1;
+}
+
+/**
  * hweightN - returns the hamming weight of a N-bit word
  * @x: the word to weigh
  *