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Sun, 26 Apr 2026 11:42:10 -0700 (PDT) Received: from localhost ([2a03:2880:10ff:7::]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7dcdbef352bsm14589116a34.10.2026.04.26.11.42.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 26 Apr 2026 11:42:10 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@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 Date: Sun, 26 Apr 2026 11:42:09 -0700 Message-Id: Cc: , , , , , , Subject: Re: [PATCH bpf-next v8 2/8] selftests/bpf: Add basic libarena scaffolding From: "Alexei Starovoitov" To: "Matt Bobrowski" , "Emil Tsalapatis" X-Mailer: aerc References: <20260421165037.4736-1-emil@etsalapatis.com> <20260421165037.4736-3-emil@etsalapatis.com> In-Reply-To: On Thu Apr 23, 2026 at 1:24 AM PDT, Matt Bobrowski wrote: >> + >> +int arena_fls(__u64 word) >> +{ >> + unsigned int num =3D 0; >> + >> + if (!word) >> + return 0; >> + >> + if (word & 0xffffffff00000000ULL) { >> + num +=3D 32; >> + word >>=3D 32; >> + } >> + >> + if (word & 0xffff0000) { >> + num +=3D 16; >> + word >>=3D 16; >> + } >> + >> + if (word & 0xff00) { >> + num +=3D 8; >> + word >>=3D 8; >> + } >> + >> + if (word & 0xf0) { >> + num +=3D 4; >> + word >>=3D 4; >> + } >> + >> + if (word & 0xc) { >> + num +=3D 2; >> + word >>=3D 2; >> + } >> + >> + if (word & 0x2) >> + num +=3D 1; >> + >> + return num + 1; >> +} > > What's your reason for not using something like __builtin_clzll() > instead here, for example: > > int arena_fls(u64 word) > { > if (!word) > return 0; > > return 64 - __builtin_clzll(word); > } Great suggestion. If it works, let's adopt __builtin_*