From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 54E7D28BA9E for ; Tue, 15 Apr 2025 12:50:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744721434; cv=none; b=Y4GuLTtX2YlKZWyXN8OFaIuqbtW5JWTDurT/7lRuctKN+WDwcpBtNmzzSU2qPcO/SMCdNml2x+vhfSGSx8R7JDPWXI78aNELpb4AqImEBF6MZRqcZMCU1ZUdv8gGWF3qvbltIX7pOn/w+L67iIlY70KUCjWggzJUjMbHyThZ5yA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744721434; c=relaxed/simple; bh=iRdjU2vjAb0W69AnpWZVkZBqUo0EN3Ufoba15vdqHwo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZL+C6pQVdz45HhgyAxQkD0UwVSLFfpjGhbn8cBLm7BkWaW0QQFOv457/9ccAl63ENGzR039zPEIEZQmEG8dYwUqU2X1yopmYL5Z+443Zac56lctYWwRBLCYto/SrJdp3w1LkrkdFmYkPh0SFaVMp8NKrJL0/Pqk4QrsxAbt7IHY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=KYx0xjJM; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="KYx0xjJM" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744721431; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=c5aGJd6gGys4y4yhW/3sEXMhbTbG/RttbuWB1PxTwu8=; b=KYx0xjJMXmTToRU1neFWCNOQtgQwIG1eBPAAHgj+/KyU12hBy3VFtRo/WqnWazPdI8A6VN DcV3VFgVD5oEDxGJpI5MSpTRrfjAZl3R/7P/6kpkHHEnIiXtq6XbPS+xlqv3ajj6XBH9Dq PXXDczNkzKeM2lnygUkgq8hqnBv/hlY= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-204-jlgSStwkNVe8jx6gyLGRtQ-1; Tue, 15 Apr 2025 08:50:29 -0400 X-MC-Unique: jlgSStwkNVe8jx6gyLGRtQ-1 X-Mimecast-MFC-AGG-ID: jlgSStwkNVe8jx6gyLGRtQ_1744721429 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-43cfda30a3cso31755685e9.3 for ; Tue, 15 Apr 2025 05:50:29 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1744721429; x=1745326229; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=c5aGJd6gGys4y4yhW/3sEXMhbTbG/RttbuWB1PxTwu8=; b=rMH//qWxahR6fmtbTZIkvi3pRbSnU2YfxS/vNURYGqHVhhMiK2ts0ErvDoVKE8Zaw9 3I7ctCnapxAhDy4Mocnp8C56MJcn4oqKReQn4WR1gndak9lAVwHm0Su0C34XcFo9BWmM 28/ZDxK5SPWd18tK+0/Orj5NCA+fM/JE8ABY0Ptj4CuU0GAvhn5zz5J8UWdX6MdflCnD 15bPIY4kKzj6INDTYMo8g2XT50Cz98zLhROIVkaCzII2bQNOuKYn834JL9YUfCtIATQ/ K4MO6ECWfofms48fngnIZpF5GfIohW9T20E2vuxXHsXRBaVcwfb5WncEq/jXfAgpUevC fJKw== X-Forwarded-Encrypted: i=1; AJvYcCXdHDadiDqYMbi/qYWa5I80iWu38sXExKNYWD8Qltpcd41A3ts5dEcl93txVpt1R4zeotUK+YX7lVgmdafmPA==@vger.kernel.org X-Gm-Message-State: AOJu0YwuDAUb/JfHlCuXtA8s0SqSczg+6oTrPy4ycjvhBqnQiZPIdSET ZW1RajbEiuAPd7Js7MYHteJFeAhmfkCmzRxkvPAcsgzCWh0Z70R80zU1Cbpu+8ac96erpDhPBX1 NXM5BN/iKkYBHneiphNRSRBiGpis2car4wZ+XRf1BTdTqL4dmGFncP+n0tmR/pXIP X-Gm-Gg: ASbGncuW6beeRzKnsu5dUiiJ8wLg0qnTrcVKiVuE8bEjEttXpB0lN9rdw/lAORz14gY shAl1HaptXc3O/L/5P5TO6dVhPXPeWl0o1rYYtDdiXFIfFZ2WeCiFf3u/LG0B6wq31NEFNJUTMu Rk2jRquKabNubJ4f2cQrSiGuIoTSOxENM5yW6JucTYeQ7ecefOlTv1cStqmBD86pKg9hXf5TGJ5 zxZuidsoHoVWbXl3TNOLlVocRoRrCoKnkeRCYe70UP6zoyH3/JIOvLm+ETpy52TUlgXMsuppnA3 nH7Lnuu18KStzUQr X-Received: by 2002:a05:600c:1c03:b0:43d:8ea:8d80 with SMTP id 5b1f17b1804b1-43f3a927654mr121649005e9.5.1744721428667; Tue, 15 Apr 2025 05:50:28 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFj25pgSIsqBjfz6Y9sBggCmIl9HsWKNdepNwC3fzn1uQR3G6mU8S+L8arQ4hueY0XNNLoU1A== X-Received: by 2002:a05:600c:1c03:b0:43d:8ea:8d80 with SMTP id 5b1f17b1804b1-43f3a927654mr121648805e9.5.1744721428360; Tue, 15 Apr 2025 05:50:28 -0700 (PDT) Received: from [192.168.10.48] ([176.206.109.83]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-43f23572c43sm213085085e9.25.2025.04.15.05.50.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Apr 2025 05:50:27 -0700 (PDT) Message-ID: <5e0754a2-ba4e-454b-99cb-57c4ae99d020@redhat.com> Date: Tue, 15 Apr 2025 14:50:26 +0200 Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: `u64` by `u64` div/mod in DRM QR for arm32 To: Jocelyn Falempe , "Russell King (Oracle)" , Christian Schrefl Cc: Miguel Ojeda , Arnd Bergmann , rust-for-linux , Linux ARM , dri-devel , Linus Walleij References: <38867e79-c0e3-4bcd-bdf9-3fb5b571d51e@gmail.com> <1a03b57c-1b5f-405a-a22a-89cc82138c55@redhat.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: <1a03b57c-1b5f-405a-a22a-89cc82138c55@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ks0QGjHEjcPgAkDvWQDINdGM3mZSp30OiLkLCDYXc7g_1744721429 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/15/25 11:14, Jocelyn Falempe wrote: > For this case, the u64 divisor "pow" is a power of 10, so can have only > a limited number of values. (17, and 9 of them can be used as u32). > Normally when the divisor is known at build time the compiler can > replace the division by a multiplication and some bit shift. > > so for 32bits machine, the match can be rewritten with constants, a bit > like this: If you add bindings to mul_u64_u64_shr from include/linux/math64.h, you can include the constants yourself: pub struct MagicMul { mult: u64, shift: u32, } // Computed using the algorithm from Hacker's Delight, 2nd ed. const DIV10: [MagicMul; 19] = [ MagicMul { mult: 0x1, shift: 0 }, MagicMul { mult: 0x6666666666666667u64, shift: 66 }, MagicMul { mult: 0xA3D70A3D70A3D70Bu64, shift: 70 }, MagicMul { mult: 0x20C49BA5E353F7CFu64, shift: 71 }, MagicMul { mult: 0x346DC5D63886594Bu64, shift: 75 }, MagicMul { mult: 0x29F16B11C6D1E109u64, shift: 78 }, MagicMul { mult: 0x431BDE82D7B634DBu64, shift: 82 }, MagicMul { mult: 0xD6BF94D5E57A42BDu64, shift: 87 }, MagicMul { mult: 0x55E63B88C230E77Fu64, shift: 89 }, MagicMul { mult: 0x112E0BE826D694B3u64, shift: 90 }, MagicMul { mult: 0x036F9BFB3AF7B757u64, shift: 91 }, MagicMul { mult: 0x00AFEBFF0BCB24ABu64, shift: 92 }, MagicMul { mult: 0x232F33025BD42233u64, shift: 101 }, MagicMul { mult: 0x384B84D092ED0385u64, shift: 105 }, MagicMul { mult: 0x0B424DC35095CD81u64, shift: 106 }, MagicMul { mult: 0x480EBE7B9D58566Du64, shift: 112 }, MagicMul { mult: 0x39A5652FB1137857u64, shift: 115 }, MagicMul { mult: 0x5C3BD5191B525A25u64, shift: 119 }, MagicMul { mult: 0x12725DD1D243ABA1u64, shift: 120 }, ]; const fn div10(val: u64, exp: u32) -> u64 { let MagicMul { mult, shift } = DIV10[exp as usize]; mul_u64_u64_shr(val, mult, shift) } #[test] fn test_div10() { assert_eq!(div10(12345678, 0), 12345678); assert_eq!(div10(12345678, 1), 1234567); assert_eq!(div10(12345678, 2), 123456); assert_eq!(div10(12345678, 3), 12345); assert_eq!(div10(12345678, 4), 1234); assert_eq!(div10(12345678, 5), 123); assert_eq!(div10(12345678, 6), 12); assert_eq!(div10(12345678, 7), 1); assert_eq!(div10(9876543298765432, 8), 98765432); assert_eq!(div10(9876543298765432, 9), 9876543); assert_eq!(div10(9876543298765432, 10), 987654); assert_eq!(div10(9876543298765432, 11), 98765); assert_eq!(div10(9876543298765432, 12), 9876); assert_eq!(div10(9876543298765432, 13), 987); assert_eq!(div10(9876543298765432, 14), 98); assert_eq!(div10(9876543298765432, 15), 9); assert_eq!(div10(12349876543298765432, 16), 1234); assert_eq!(div10(12349876543298765432, 17), 123); assert_eq!(div10(12349876543298765432, 18), 12); } I tried the test in userspace with this implementation of the function: #![feature(bigint_helper_methods)] const fn mul_u64_u64_shr(m: u64, n: u64, s: u32) -> u64 { let (a, b) = m.widening_mul(n); if s == 0 { a } else if s < 64 { (a >> s) | (b << 64 - s) } else { b >> (s - 64) } } HTH, Paolo