From: Stephen Hemminger <shemminger@osdl.org>
Date: Fri, 6 Jan 2006 08:12:12 +0000 (-0800)
Subject: [PATCH] x86: fls() in asm
X-Git-Tag: v2.6.16-rc1~936^2~185
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d832245d7cc16d50b29c1b708ccbe9c75ac376a3;p=linux-2.6

[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>
---

diff --git a/include/asm-i386/bitops.h b/include/asm-i386/bitops.h
index 26eb981171..65679aca4b 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__
@@ -414,6 +409,23 @@ static inline int ffs(int x)
 	return r+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"
+		"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