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[patch 14/47] generic ffs()

To: linux-kernel@vger.kernel.org
Subject: [patch 14/47] generic ffs()
From: Akinobu Mita <mita@miraclelinux.com>
Date: Tue, 14 Feb 2006 14:04:05 +0900
Cc: akpm@osdl.org, Greg Ungerer <gerg@uclinux.org>, linux-mips@linux-mips.org, sparclinux@vger.kernel.org, ultralinux@vger.kernel.org, Akinobu Mita <mita@miraclelinux.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20060214050351.252615000@localhost.localdomain>
Sender: linux-mips-bounce@linux-mips.org
This patch introduces the C-language equivalent of the function:
int ffs(int x);

In include/asm-generic/bitops/ffs.h

This code largely copied from:
include/linux/bitops.h

Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
 include/asm-generic/bitops/ffs.h |   41 +++++++++++++++++++++++++++++++++++++++
 1 files changed, 41 insertions(+)

Index: 2.6-rc/include/asm-generic/bitops/ffs.h
===================================================================
--- /dev/null
+++ 2.6-rc/include/asm-generic/bitops/ffs.h
@@ -0,0 +1,41 @@
+#ifndef _ASM_GENERIC_BITOPS_FFS_H_
+#define _ASM_GENERIC_BITOPS_FFS_H_
+
+/**
+ * ffs - find first bit set
+ * @x: the word to search
+ *
+ * This is defined the same way as
+ * the libc and compiler builtin ffs routines, therefore
+ * differs in spirit from the above ffz (man ffs).
+ */
+static inline int ffs(int x)
+{
+       int r = 1;
+
+       if (!x)
+               return 0;
+       if (!(x & 0xffff)) {
+               x >>= 16;
+               r += 16;
+       }
+       if (!(x & 0xff)) {
+               x >>= 8;
+               r += 8;
+       }
+       if (!(x & 0xf)) {
+               x >>= 4;
+               r += 4;
+       }
+       if (!(x & 3)) {
+               x >>= 2;
+               r += 2;
+       }
+       if (!(x & 1)) {
+               x >>= 1;
+               r += 1;
+       }
+       return r;
+}
+
+#endif /* _ASM_GENERIC_BITOPS_FFS_H_ */

--

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