[PATCH] bitops: generic __ffs()

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

1 files changed, 43 insertions, 0 deletions

diff --git a/include/asm-generic/bitops/__ffs.h b/include/asm-generic/bitops/__ffs.h
new file mode 100644
index 00000000000..9a3274aecf8
--- /dev/null
+++ b/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_ */