| From | "Srivatsa S. Bhat" <> | Subject | [RFC PATCH v4 10/40] bitops: Document the difference in indexing between fls() and __fls() | Date | Thu, 26 Sep 2013 04:45:56 +0530 |
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fls() indexes the bits starting with 1, ie., from 1 to BITS_PER_LONG whereas __fls() uses a zero-based indexing scheme (0 to BITS_PER_LONG - 1). Add comments to document this important difference.
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
arch/x86/include/asm/bitops.h | 4 ++++ include/asm-generic/bitops/__fls.h | 5 +++++ 2 files changed, 9 insertions(+)
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h index 41639ce..9186e4a 100644 --- a/arch/x86/include/asm/bitops.h +++ b/arch/x86/include/asm/bitops.h @@ -388,6 +388,10 @@ static inline unsigned long ffz(unsigned long word) * @word: The word to search * * Undefined if no set bit exists, so code should check against 0 first. + * + * Note: __fls(x) is equivalent to fls(x) - 1. That is, __fls() uses + * a zero-based indexing scheme (0 to BITS_PER_LONG - 1), where + * __fls(1) = 0, __fls(2) = 1, and so on. */ static inline unsigned long __fls(unsigned long word) { diff --git a/include/asm-generic/bitops/__fls.h b/include/asm-generic/bitops/__fls.h index a60a7cc..ae908a5 100644 --- a/include/asm-generic/bitops/__fls.h +++ b/include/asm-generic/bitops/__fls.h @@ -8,6 +8,11 @@ * @word: the word to search * * Undefined if no set bit exists, so code should check against 0 first. + * + * Note: __fls(x) is equivalent to fls(x) - 1. That is, __fls() uses + * a zero-based indexing scheme (0 to BITS_PER_LONG - 1), where + * __fls(1) = 0, __fls(2) = 1, and so on. + * */ static __always_inline unsigned long __fls(unsigned long word) {
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