From: Stephen Hemminger <shemminger@osdl.org>
To: Linus Torvalds <torvalds@osdl.org>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] fls in asm for i386
Date: Fri, 2 Dec 2005 16:22:40 -0800 [thread overview]
Message-ID: <20051202162240.746c436e@localhost.localdomain> (raw)
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>
--- orig/include/asm-i386/bitops.h
+++ new/include/asm-i386/bitops.h
@@ -367,12 +367,6 @@ static inline unsigned long ffz(unsigned
return word;
}
-/*
- * fls: find last bit set.
- */
-
-#define fls(x) generic_fls(x)
-
#ifdef __KERNEL__
/*
@@ -414,6 +408,23 @@ 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
*
next reply other threads:[~2005-12-03 0:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-03 0:22 Stephen Hemminger [this message]
2005-12-03 0:24 ` [PATCH] fls in asm for x86_64 Stephen Hemminger
2005-12-03 1:44 ` Andi Kleen
2005-12-05 13:46 ` [PATCH] fls in asm for i386 Pádraig Brady
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