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Bhat" Subject: [RFC PATCH v4 10/40] bitops: Document the difference in indexing between fls() and __fls() To: akpm@linux-foundation.org, mgorman@suse.de, dave@sr71.net, hannes@cmpxchg.org, tony.luck@intel.com, matthew.garrett@nebula.com, riel@redhat.com, arjan@linux.intel.com, srinivas.pandruvada@linux.intel.com, willy@linux.intel.com, kamezawa.hiroyu@jp.fujitsu.com, lenb@kernel.org, rjw@sisk.pl Cc: gargankita@gmail.com, paulmck@linux.vnet.ibm.com, svaidy@linux.vnet.ibm.com, andi@firstfloor.org, isimatu.yasuaki@jp.fujitsu.com, santosh.shilimkar@ti.com, kosaki.motohiro@gmail.com, srivatsa.bhat@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Thu, 26 Sep 2013 04:45:56 +0530 Message-ID: <20130925231554.26184.87472.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20130925231250.26184.31438.stgit@srivatsabhat.in.ibm.com> References: <20130925231250.26184.31438.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13092523-6102-0000-0000-0000043C7F5C Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Spam-Status: No, score=-5.5 required=5.0 tests=BAYES_00,KHOP_BIG_TO_CC, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 --- arch/x86/include/asm/bitops.h | 4 ++++ include/asm-generic/bitops/__fls.h | 5 +++++ 2 files changed, 9 insertions(+) -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html 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) {