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[1.175.176.70]) by smtp.gmail.com with ESMTPSA id u127-20020a637985000000b005cd8044c6fesm10411263pgc.23.2024.04.17.06.25.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Apr 2024 06:25:44 -0700 (PDT) From: Chin-Chun Chen To: yury.norov@gmail.com Cc: linux@rasmusvillemoes.dk, linux-kernel@vger.kernel.org, Chin-Chun Chen Subject: [PATCH] linux/bitops.h: Refactor function fns to reduce branch usage and eliminate external calls Date: Wed, 17 Apr 2024 21:22:54 +0800 Message-Id: <20240417132252.20773-1-chinchunchen2001@gmail.com> X-Mailer: git-send-email 2.40.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Rewrote the function fns to use macro wrote in linux/include/asm-generic/bi= tops/const_hweight.h Decrease the number of required branches and eliminate the need for externa= l calls. The number of branches is now constant, unaffected by input variations. This commit improves code efficiency and clarity. Signed-off-by: Chin-Chun Chen --- include/linux/bitops.h | 54 +++++++++++++++++++++++++++++++++++++----- 1 file changed, 48 insertions(+), 6 deletions(-) diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 5842d7d03f19..18899f11aaa7 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -247,6 +247,13 @@ static inline unsigned long __ffs64(u64 word) return __ffs((unsigned long)word); } =20 + +#define __const_hweight2(w) = \ + ((unsigned int) (!!((word) & (1ULL << 0))) + (!!((word) & (1ULL << 1))= )) + +#define __const_hweight4(w) = \ + ((unsigned int) (!!((word) & (1ULL << 0))) + (!!((word) & (1ULL << 1))= ) + \ + (!!((word) & (1ULL << 2))) + (!!((word) & (1ULL << 3)= ))) /** * fns - find N'th set bit in a word * @word: The word to search @@ -255,13 +262,48 @@ static inline unsigned long __ffs64(u64 word) static inline unsigned long fns(unsigned long word, unsigned int n) { - unsigned int bit; - - while (word) { - bit =3D __ffs(word); - if (--n =3D=3D 0) - return bit; - __clear_bit(bit, &word); - return BITS_PER_LONG; + unsigned int bits; + unsigned int sum =3D 0; +#if BITS_PER_LONG =3D=3D 64 + bits =3D __const_hweight32(word & 0xffffffff); + if (bits <=3D n) { + n -=3D bits; + word >>=3D 32; + sum +=3D 32; + } +#endif + bits =3D __const_hweight16(word & 0xffff); + if (bits <=3D n) { + n -=3D bits; + word >>=3D 16; + sum +=3D 16; + } + bits =3D __const_hweight8(word & 0xff); + if (bits <=3D n) { + n -=3D bits; + word >>=3D 8; + sum +=3D 8; + } + bits =3D __const_hweight4(word & 0xf); + if (bits <=3D n) { + n -=3D bits; + word >>=3D 4; + sum +=3D 4; + } + bits =3D __const_hweight2(word & 0x3); + if (bits <=3D n) { + n -=3D bits; + word >>=3D 2; + sum +=3D 2; + } + bits =3D (unsigned int) (word & 0x1); + if (bits <=3D n) { + n -=3D bits; + word >>=3D 1; + sum +=3D 1; + } + bits =3D (unsigned int) (word & 0x1); + if (bits <=3D n) { + n -=3D bits; + sum +=3D 1; + } + + if (!n) + return sum; + + return BITS_PER_LONG; } --=20 2.40.1