From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1A68C41B343 for ; Tue, 20 Jan 2026 23:49:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768952989; cv=none; b=kQrICeBbMcPUDavyHhtDtcg8nso3OqAF/JMPNnBVrqryX97FzvMjmTcKp2NzKMmAwcuVsxGGXvDdo9IJuDvdE0T2E629pSUWL/STa72T6ZIpPH078uJO08vNqpak6qr0udCyzZ7zLa4xT21+Hp5UTlv3jW8g7t8hVN46mAg2PqA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768952989; c=relaxed/simple; bh=Av8WdQG0gigU5VjF9aHaxP/X/C1aAL8YSMJ+uWv/Imk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=B7Bqfiaq5+1b7M3j2iTbSydVwnH245gyLCcY77UtpqMJHfOKSMUqXJr8CKH1UhuHxc7TFoxxXFonYnr1u9aenRv5y8T4tvqmuePNeNhzjz6KR+lQzcKr0yPJp3LgbXhwe6Vx+k0WFUOo0NjFEUPTAtwr9XlRJl+i0/3LH6j8G6k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=aBT5JOtf; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="aBT5JOtf" Received: from [IPV6:2601:646:8081:9483:12c5:bc8e:d949:3497] ([IPv6:2601:646:8081:9483:12c5:bc8e:d949:3497]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 60KNn6GI133750 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Tue, 20 Jan 2026 15:49:13 -0800 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 60KNn6GI133750 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025122301; t=1768952953; bh=1tQpdMaxh7EduAyYUutL6w1twNQKFHvPqtSkxOgecIM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=aBT5JOtfwFfHQdJVcjInmAA8F9u0B9Ad9WBsBjvjfy3NFB9R3XSy3Fa+F7J01t1Gi mVdwxsZSGBVDwFg+Qt+/uwXiExHQrnM8Q/6FgkIVQpTv4XTS7o9INBkYRtO9c29Z5i xz3ndM9X3/5jHU2EUKjQ3Gn2wqZQocMNmTnDtA7oDsg7/b8ArWD7+kyO4O4ZnTj9yj HPrKC/8VKBlwyqojtSodxKJFGZx5tV1rRNPlADAqDjDdYEyFNGerOcHrbmqVmrgCNu 4Ig4ZrNDZXoWoy418TIGrafS9Vn2J4fS0HrhbnQmNHzG2yt3Kzep6O72H8LutD+CBz SwS/24xbqvk3w== Message-ID: <8923623d-1a23-483d-add7-2fd03a3a2c3d@zytor.com> Date: Tue, 20 Jan 2026 15:49:01 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] x86/lib: Optimize num_digits() and fix INT_MIN overflow To: David Desobry , David Laight Cc: tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org References: <20260120174748.302078-1-david.desobry@formalgen.com> <20260120214612.73b83cbe@pumpkin> Content-Language: en-US, sv-SE From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2026-01-20 15:32, David Desobry wrote: > > Good catch. I have replaced the switch statement with a linear if-chain in v3 > to ensure better code generation for both GCC and Clang. > I think a bigger deal is just to change it to unsigned. Now, for really silly optimization: int num_digits(unsigned int x) { int n = 0; asm("cmp %2,%1; sbb $-2,%0" : "+r" (n) : "r" (x), "g" (10)); asm("cmp %2,%1; sbb $-1,%0" : "+r" (n) : "r" (x), "g" (100)); asm("cmp %2,%1; sbb $-1,%0" : "+r" (n) : "r" (x), "g" (1000)); asm("cmp %2,%1; sbb $-1,%0" : "+r" (n) : "r" (x), "g" (10000)); asm("cmp %2,%1; sbb $-1,%0" : "+r" (n) : "r" (x), "g" (100000)); asm("cmp %2,%1; sbb $-1,%0" : "+r" (n) : "r" (x), "g" (1000000)); asm("cmp %2,%1; sbb $-1,%0" : "+r" (n) : "r" (x), "g" (10000000)); asm("cmp %2,%1; sbb $-1,%0" : "+r" (n) : "r" (x), "g" (100000000)); asm("cmp %2,%1; sbb $-1,%0" : "+r" (n) : "r" (x), "g" (1000000000)); return n; } No branches at all! -hpa