[patch 07/44] generic __ffs()

Akinobu Mita
2006-02-01T09:21:06Z

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This patch introduces the C-language equivalent of the function:
unsigned long __ffs(unsigned long word);

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

This code largely copied from:
include/asm-sparc/bitops.h

Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
include/asm-generic/bitops/__ffs.h | 43 +++++++++++++++++++++++++++++++++++++
1 files changed, 43 insertions(+)

Index: 2.6-git/include/asm-generic/bitops/__ffs.h
===================================================================
--- /dev/null
+++ 2.6-git/include/asm-generic/bitops/__ffs.h
@@ -0,0 +1,43 @@
+#ifndef _ASM_GENERIC_BITOPS___FFS_H_
+#define _ASM_GENERIC_BITOPS___FFS_H_
+
+#include <asm/types.h>
+
+/**
+ * __ffs - find first bit in word.
+ * @word: The word to search
+ *
+ * Undefined if no bit exists, so code should check against 0 first.
+ */
+static inline unsigned long __ffs(unsigned long word)
+{
+ int num = 0;
+
+#if BITS_PER_LONG == 64
+ if ((word & 0xffffffff) == 0) {
+ num += 32;
+ word >>= 32;
+ }
+#endif
+ if ((word & 0xffff) == 0) {
+ num += 16;
+ word >>= 16;
+ }
+ if ((word & 0xff) == 0) {
+ num += 8;
+ word >>= 8;
+ }
+ if ((word & 0xf) == 0) {
+ num += 4;
+ word >>= 4;
+ }
+ if ((word & 0x3) == 0) {
+ num += 2;
+ word >>= 2;
+ }
+ if ((word & 0x1) == 0)
+ num += 1;
+ return num;
+}
+
+#endif /* _ASM_GENERIC_BITOPS___FFS_H_ */

--