generic: introduce a generic __fls implementation
Alexander van Heukelum [Sat, 15 Mar 2008 17:30:57 +0000 (18:30 +0100)]
Add a generic __fls implementation in the same spirit as
the generic __ffs one. It finds the last (most significant)
set bit in the given long value.

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/asm-generic/bitops/__fls.h [new file with mode: 0644]

diff --git a/include/asm-generic/bitops/__fls.h b/include/asm-generic/bitops/__fls.h
new file mode 100644 (file)
index 0000000..be24465
--- /dev/null
@@ -0,0 +1,43 @@
+#ifndef _ASM_GENERIC_BITOPS___FLS_H_
+#define _ASM_GENERIC_BITOPS___FLS_H_
+
+#include <asm/types.h>
+
+/**
+ * __fls - find last (most-significant) set bit in a long word
+ * @word: the word to search
+ *
+ * Undefined if no set bit exists, so code should check against 0 first.
+ */
+static inline unsigned long __fls(unsigned long word)
+{
+       int num = BITS_PER_LONG - 1;
+
+#if BITS_PER_LONG == 64
+       if (!(word & (~0ul << 32))) {
+               num -= 32;
+               word <<= 32;
+       }
+#endif
+       if (!(word & (~0ul << (BITS_PER_LONG-16)))) {
+               num -= 16;
+               word <<= 16;
+       }
+       if (!(word & (~0ul << (BITS_PER_LONG-8)))) {
+               num -= 8;
+               word <<= 8;
+       }
+       if (!(word & (~0ul << (BITS_PER_LONG-4)))) {
+               num -= 4;
+               word <<= 4;
+       }
+       if (!(word & (~0ul << (BITS_PER_LONG-2)))) {
+               num -= 2;
+               word <<= 2;
+       }
+       if (!(word & (~0ul << (BITS_PER_LONG-1))))
+               num -= 1;
+       return num;
+}
+
+#endif /* _ASM_GENERIC_BITOPS___FLS_H_ */