[PATCH] bitops: generic ffs()

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

diff --git a/include/asm-generic/bitops/ffs.h b/include/asm-generic/bitops/ffs.h
new file mode 100644 (file)
index 0000000..fbbb43a
--- /dev/null
+++ b/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_ */