From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from NAM02-DM3-obe.outbound.protection.outlook.com (mail-dm3nam02on2068.outbound.protection.outlook.com [40.107.95.68]) (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 4726F2E11D8; Fri, 13 Jun 2025 14:16:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.95.68 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749824185; cv=fail; b=fMEUPVACKt3yy/VSUpXnanNw2lgiYVPLWpmCxO4NpLaSuI4MEf++YguTQn9mNHLDolIq3JTTUCGN82obaBuVnYgpjFgoVEdN6jXx58pzIDxhxy3HXPOsWsFzLSeI1in/o8KlqNWuEK+d07pDiKVW0cgC3ekOo5Mx1d/DGUZ2Smc= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749824185; c=relaxed/simple; bh=GNMU8XTDCjj5vYmAlim+yo5JDchauQZ17lp+WfIBi1Y=; h=Content-Type:Date:Message-Id:Subject:From:To:Cc:References: In-Reply-To:MIME-Version; b=a11qtMuZfETpfCTZxgeweiYD+1xf1YhxJ471i1uQAjIRqnJ8pE85YGv1NO3flkaC8kLLJsfNuOaAI6wVE2kJ4IvbsJ4qG+EOo4perHJdYCBmeb7Sl4Zit5IKNI9fXgPWP6vXSrqIpVVfSXnILOypCXh3cB7oLy3Ko/Lz5hLWRdw= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=lIZBr1Y+; arc=fail smtp.client-ip=40.107.95.68 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="lIZBr1Y+" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=CQkFgyQhvXJj1i0bG3+HHLpmnewb8LNQhmRzS/xwoYfFUBIGuo78PxFigblm0FQSO28gF3yqY6lDNVN5gHRVO7jzhsC/Dpqlk4diW56I8ICotrajiqWOYv06+YVU1X32WQwcfqIqYbC3eEJacwySbKTSibpwOP/NYzXn8rfcJWr+4+Sac1P0DFzsCG5Wsuq9kbPQ5u6W960I3eyAFIeAwvKtZs/AsFFmSXqqnr0RrdN0uRQ6PzELOf0/tSDurQXMP/40D+8HolenwZ1RNQmgCi+vGKvAgYOcDvzghV0SUcychZ6wRuO6WzJta8xgmsHNE+XmuwpsvfZpIo9mdDvwPw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=+iAreg8rNyRX77tlTfIV4xV6vzcab1XMnf7PNNQTTus=; b=nPtof24OSnP9LSugyE22pr9VsC/Xzp2l9W08DiqiS2xJG5Jn2bdMFnG+WIXH3UMR7ief7Hr5mHV9LovKW+tkwMDmHrkVVWAlkcmnhQjADH8ZREknYDNEY01ntdGToUBeQK4xj24lbB3w79sHZLPb92bvzL0e7O872QdGA5zgeAc8ugwvEci9nbv8hIjNwWXeOLhEf6U54DGewzbElESwkPTOtWVojg8SJSQp36Y9ulXiV0t/P12/xy3nONP+ZaXtvPP/Kq9e5lxligq+qgcHnthj+CW+w60qFMUgxiEemutsrcT5NWUz9CGWiHTP9JY9VpU8HclaX37i6f4Q0qs5cQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=+iAreg8rNyRX77tlTfIV4xV6vzcab1XMnf7PNNQTTus=; b=lIZBr1Y+gzIirAnc/3rXRjp0Rs/Lcs1FuC4CbNAx4npYi8u6NvRx9BhimvO6zSYyBURnYeXn/bn6VdzDgX+iIyqUfymp88A2xRAdOwy6oiiHT/wo8KrzJLdjSBmD1i1ilWsqzGwYrzrOVJy04bjIVYjT5peRW8+NBY1UUwb/Sls3KfQtDIo4gP1U5pkVFSG+pRy3VxVODOmYEJgS7otC6aqm1CXwMeuYmtTQ/7lOi+VZu9/d7uefYWdFS3SgjRizLRg2UswCxdO6X2ISI6Yw5P7nr3DJwVZ4ZvsPqvA0BMpj3Wg4RJwk9ArXGwyD3P0WJe4xInBaQPI5pA4Lf1oASg== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) by PH7PR12MB7355.namprd12.prod.outlook.com (2603:10b6:510:20e::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8835.23; Fri, 13 Jun 2025 14:16:14 +0000 Received: from CH2PR12MB3990.namprd12.prod.outlook.com ([fe80::6e37:569f:82ee:3f99]) by CH2PR12MB3990.namprd12.prod.outlook.com ([fe80::6e37:569f:82ee:3f99%4]) with mapi id 15.20.8835.018; Fri, 13 Jun 2025 14:16:14 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 13 Jun 2025 23:16:10 +0900 Message-Id: Subject: Re: [PATCH v5 04/23] rust: add new `num` module with `PowerOfTwo` type From: "Alexandre Courbot" To: "Boqun Feng" Cc: "Miguel Ojeda" , "Alex Gaynor" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Danilo Krummrich" , "David Airlie" , "Simona Vetter" , "Maarten Lankhorst" , "Maxime Ripard" , "Thomas Zimmermann" , "Benno Lossin" , "John Hubbard" , "Ben Skeggs" , "Joel Fernandes" , "Timur Tabi" , "Alistair Popple" , , , , X-Mailer: aerc 0.20.1-0-g2ecb8770224a References: <20250612-nova-frts-v5-0-14ba7eaf166b@nvidia.com> <20250612-nova-frts-v5-4-14ba7eaf166b@nvidia.com> In-Reply-To: X-ClientProxiedBy: TYCPR01CA0023.jpnprd01.prod.outlook.com (2603:1096:405::35) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|PH7PR12MB7355:EE_ X-MS-Office365-Filtering-Correlation-Id: ba09e14e-f250-47df-a9b0-08ddaa84da53 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016|10070799003; X-Microsoft-Antispam-Message-Info: =?utf-8?B?VUUzVlg3S0N2SnY4VGVROGJEUlIvcUs2ekQvN1Qyb2N4VEF5blVzS2E3N2ZE?= =?utf-8?B?MmJ1S1ZxMDU5ZTgyM3pUZTZmdUp3V0ZVYnh5SXM1OG95aUlTVlBEUVFScUF3?= =?utf-8?B?dThFZmRIUGJjbVZDd0h2NHoyRHJ5OWE5TWQvZStXTWM2T3dGMzdESlpPNGVn?= =?utf-8?B?TlVlMlpaQXNMUVpTbVlFU2FRKzdsakJ6bm5yQ3AxeHdEQzM2bGlCbGJOWTFh?= =?utf-8?B?b1BGYUhTVW1NNjR4K2JTZHFJOURiSW1nSGNvdUloYW12SDJ6T3R2Y1lKb2Fm?= =?utf-8?B?VThpQVRFQUZ0VWJPWk1tWldQMTZJa1ZGcDRTRWJZNzN0blJzKzkwdElQMjJs?= =?utf-8?B?ajZEUzA4L0NlZyt0WlJ2MnlFNUxaTWg3ajI2MTF5Q21NQVlaM05rUHBnSEtu?= =?utf-8?B?Rk1Yd25Sakl1Vmoyd2UyaGhSQ1lZN3JwSFhiWXNmOTdOV1NXK3Q2RlBZdE1E?= =?utf-8?B?dVcrMnhRWEN2UFo0RW9FT3hCK015WnorYWpKazBHMzY5YkV6M1ptbkZnRGlV?= =?utf-8?B?K0hjRlBpblJLZ1VQT0xBWWg4eUJmRTFick1lVVEyMUtkM09qbERCZWZXaTRm?= =?utf-8?B?Z2xrK3l3bzljNnQzL09UUFJJNjltVC9JZi92MFJNMXdkS3YrbFBNWXhtNEU2?= =?utf-8?B?S2tZWWFBbitYdjc5SkF3WnlHa2xXd3AwVWl1cU9kVS9YbHFSbWgwbFc0ZWF2?= =?utf-8?B?Um52MXlTU3FGRVMwOFpNbXlucFlPdURFeUFWVFRDdEhra0wzK3U0RzFHL0RI?= =?utf-8?B?QVRrTEhkMHFoNG5vTkN4eWZCdlcwdkVWRlptNVNsNjI0eXJQdVNlWGFMQ0Rm?= =?utf-8?B?NDM4TkJpTzROc0VPZENEUTJFanJMKytJdHZXdmxrSjFqZGZhcTdCMThGTkcx?= =?utf-8?B?OHREMkRNQzRjTUM2Q3oycmNQdnlSS083NXF2YzN0UFcyZWlOb2NDMTdDTjVS?= =?utf-8?B?NWZxQUF2dmNtVjU1UC9TTElVZGpVbUFVUXZ3STBjSFZPSmE2anBDNkwybGQz?= =?utf-8?B?aEVnTGYwWUFDd1I5SlQ4dzNKWGJ4djE1QmxkZXJBeWVSVTFrYmpSY1MrdU9D?= =?utf-8?B?V29KaE1xYjVZRzB3SGlGa1JJTXQvM0E4SzJsZEZJaFcrZThCWjZ2cysrb3g3?= =?utf-8?B?cXh3ZldBMjFuZHZ4ZWxGVS83R2VEbFF3a2dXNm9FUUtyVktBVlUxaXY5Skpx?= =?utf-8?B?Ukd4QWIrM1ZXdXg4VzBuM3IycTR3TituYnhlVTJHeFFvR3FIZGRFdE4zQ0VF?= =?utf-8?B?NGhJSzRMcjJ2aDNTbEhnR2ZSbTJtVzg5QlVkTEJmSHRscnY2ekdyelJNQzdi?= =?utf-8?B?VktmYjF4dlBkSnZsNHRaWkFyVS9YcjhLZFBoV2RoeHdVaUdMVm1sNFZNZ1J3?= =?utf-8?B?aEFvaFRyYU5KNFJPYkUyalB5VEZnWmNiVHlRU01MdzJVQ2tzRlp0cGVNZGlN?= =?utf-8?B?Mzl5VXJlOUd2b2l1L3VwdGFQYzU4QjNzRFZmYzV5R3p0OU9PNnhXV0F5dGxy?= =?utf-8?B?ZUM0Q0krak1GcXFob0tMZjFmaTVkUHdxZ2tPWHNJN28yV2RQb3g3WUtGeUQx?= =?utf-8?B?SmFXb0FESzQwaXlqcFdTV0VCdEtYRmtIOUgzeFZEc2h3K0RRS254NkdWN3hH?= =?utf-8?B?VWo4RXU2U09aZUJiYWF1eW9FcmxXbEpGcElseUZ2NFFFOXhmTlgrSDVoVDNG?= =?utf-8?B?WnlaSEJ3T3FVU05QRmVJRmZlQ21TRHdCQWxsVkE1WTNtVnRMYlo2RXEzTExr?= =?utf-8?B?OFBWeXNra2d5MWc4REVleFUvbVc0UHBtOHl4OUtWd210NnVuVG1PeEgreUw2?= =?utf-8?B?a3JTaUo2VElNUWMrNnFqdXh4ZXNzVmRtS09BUU0vU1poVFdYRWdYYkJZbFI5?= =?utf-8?B?dDFjNlZSNW1OOTl2VisxTTc1ZytMMVlQbm8wZVlzNmZQR0E9PQ==?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH2PR12MB3990.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(376014)(7416014)(366016)(10070799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?S2dsNVY4T2xYWnY5clhVN0phUnhNd1RmR0NmOFZzMlJJZFJEUEhjVk5OQjEw?= =?utf-8?B?ZFNma0k4Q3pxOVM3dWZFb2FIeDRCWXEwNWZLTkJUblplenJ1RU5LY2lPWkU1?= =?utf-8?B?dVA1L3JJWGNFWnpzWWt2U3c2QUJsTWVHZnlWUU9qeXk2Q2FqczBNRXh6ZmYz?= =?utf-8?B?b0RTaDhSalNBRUtBOXdRbmRoMmYvQ253V3p2cVBGUUxPd3llZW9LbFRTaDJu?= =?utf-8?B?MFIwOUYvU0pFcnFaeTBrUkQvSDBmZXhoRWt5Nm1MNS9FdkdyanFpWDhxUUVB?= =?utf-8?B?cmV1bWNUNmZFTDQvejQxNUtlZE5YbERmaVNhK2hpeGhxcTFKVUdyUVlibmNT?= =?utf-8?B?dE1VQVN5NWNyYUlpQUJIdWxwWXZvUHRnMlhPN0RXRWlkT3pzNVBqNkhmSlE1?= =?utf-8?B?UGxBU1RqYk1rNmExa0g4R01VNExJbEE5TEFVbnoranhCeXQzdlVkdDlyellL?= =?utf-8?B?dVJFWTgzR2J0UnllTlo2OXowWGFyMWVHSXdiNmRTblU1RWNiaElZdWwrQ0du?= =?utf-8?B?R3hCdDZrblFLSnB4RHkxQmFLNDIycjYxRHNWU2R0VVl3bFpxZUdnRGw5TjNl?= =?utf-8?B?WXN6Nm1Uc3FuaHhjWmV0a2JvMjcwV1g2WDkzODZUWElUczd6ZmE4OERKUkJ4?= =?utf-8?B?L2l1dzJSTlZFb2hvbXVmZUl0Mm44K0k2c2wwV0wzOW5oa3JwaVBuamtyK0lZ?= =?utf-8?B?VkZyK0hsM2VPRndscWdTRnIzOVBJZWhNYlV6UC9qMUVmUjNSbTI1WTRpNUZn?= =?utf-8?B?OEdiMHRFanBxeHBQbWNnaGZoQk9XMXQ1Z1N2Y3djb0h3WTNmTjNLZFFlNG85?= =?utf-8?B?a2VwWERVa25XcGs3MDYraHhhYXpLVjF3T2R0UHJyZ1VPek9UclAzR0tlZlVj?= =?utf-8?B?YWFsK1J2ZDN1SDdMd1NCQVU3cWw3cHNGOC9CeWVKOStxbXBwazFQNUhaVGpL?= =?utf-8?B?c3liQkl4dHVMblM5a3N5YStxQVlDN2Zrd2ZJRldWYnRzUS8vVEtyWEszRmpo?= =?utf-8?B?Ni9QNEQyNE5MbDZQbE9NOXcwNVh2MDdzWjhRTXJsYjVVWXpvSnlockNCMGN1?= =?utf-8?B?c3dPMXF5a2NTTmhHcTN5OEFmcW5yN1UzK1Q1dkpWZmxET21say9LcGJWY0xU?= =?utf-8?B?cDBqc0MzTTJaTnRSTjlVZHlMczdIbWM5M3JQUzVtdnVNemRTa1p3VzNya0RL?= =?utf-8?B?NWRVSFB1N1hZaTk3RkxzTWg2OHZWMlIyZ0Jiekcza3JFNzNSQS9weWlwWC9h?= =?utf-8?B?bVFUR0RqQmFyQ0VFYkFNUU1aSm56KzhvYXNGYkhhS2hWNTJJd3p0S0ZjU3hi?= =?utf-8?B?VWdaNjBWbnk3ZzNvUkdnYzJUUEpxV2wraU5CaytUUXJqWjBpMi92Y3BsYUxN?= =?utf-8?B?SXhHRVVxN3VBblBlYnN1K1lzcE9peE1BNEFGS0o1V3FxaGJ0M21iMjU3ZU95?= =?utf-8?B?aXFvT1VqMWRWTzByajFYUDNoOVpCV29FQlczUmdDU0cwaWZ5cVNFRkJTbS9Z?= =?utf-8?B?dmpVWnRPVXlRSTdxSG5naDNKNDVOaVYrWjJMeEtJS1VmQzZRR1NQdGw0cDVu?= =?utf-8?B?U2VpR210aXdqOWNaYXkvam9KUzQwdkVGMjhoREg4TVlrVGVqRkQwZU5nb0x4?= =?utf-8?B?T1FVRzMvODVYZ1F1dzY3VGRSRktXWVFmakltemVqcGg2OEpOSzlvMmtjTjZ1?= =?utf-8?B?eXhycVdURnlTUFl5SEwzczhkN1Zsd1ovNUFTVzdHRzBrOXU3cERYbFBHcXRy?= =?utf-8?B?UmVoUFJDZXhuS3ZWaWh3YUYyOXVBOGk0VjdPOU8ycE9CdXliSE1MZndjb2kw?= =?utf-8?B?SXlxTGJicWx1amVvZ2RnOC96eTl4dzB0b0FaNGFQZ3pWWHNPZHladm5DTFB5?= =?utf-8?B?NTRFSW1VM3FLUEFFcUtvZ1ZZVExTVWo5cTRWTjIrVXpncnpOK3FJbUErQmdi?= =?utf-8?B?Z2JTT2JYOW1oZVZrZEU2Yk5MUDJlNmM5VVlaOHphYXVBNk8rdFZpK0hycDNY?= =?utf-8?B?bUhiVVplWk50dDdpcVlWUGZNT1pqUzRVUURYWm44YUViS29pMmMxcUJLRnhk?= =?utf-8?B?eWdYbWdUZkZENktrcWhuUGlkMi9JSHZ2UVBiblZXa2RPUXlQTnVxV2ZvVTZi?= =?utf-8?B?cUJUQnBqYy9BRkYwWjRDaThWdG02Z1cvOHRENnNzRUlJZCs2Smh4UFY5MCtj?= =?utf-8?Q?ePT/4IXd7dT5MPZs55SPR2K+C6N7Xc06n5ZkizvxNqbG?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: ba09e14e-f250-47df-a9b0-08ddaa84da53 X-MS-Exchange-CrossTenant-AuthSource: CH2PR12MB3990.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Jun 2025 14:16:14.2188 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 2Ml4aOgRSxt+oFgpDL4dyrq14c1SujbKGCqYcCLSpyz6laCsVDtDYEQWm5lofeeaQWT0DtvJstrLJin8xgGUAw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB7355 On Fri Jun 13, 2025 at 12:07 AM JST, Boqun Feng wrote: > On Thu, Jun 12, 2025 at 11:01:32PM +0900, Alexandre Courbot wrote: >> Introduce the `num` module, featuring the `PowerOfTwo` unsigned wrapper >> that guarantees (at build-time or runtime) that a value is a power of >> two. >>=20 >> Such a property is often useful to maintain. In the context of the >> kernel, powers of two are often used to align addresses or sizes up and >> down, or to create masks. These operations are provided by this type. >>=20 >> It is introduced to be first used by the nova-core driver. >>=20 >> Signed-off-by: Alexandre Courbot >> --- >> rust/kernel/lib.rs | 1 + >> rust/kernel/num.rs | 173 ++++++++++++++++++++++++++++++++++++++++++++++= +++++++ >> 2 files changed, 174 insertions(+) >>=20 >> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs >> index 6b4774b2b1c37f4da1866e993be6230bc6715841..2955f65da1278dd4cba1e427= 2ff178b8211a892c 100644 >> --- a/rust/kernel/lib.rs >> +++ b/rust/kernel/lib.rs >> @@ -89,6 +89,7 @@ >> pub mod mm; >> #[cfg(CONFIG_NET)] >> pub mod net; >> +pub mod num; >> pub mod of; >> #[cfg(CONFIG_PM_OPP)] >> pub mod opp; >> diff --git a/rust/kernel/num.rs b/rust/kernel/num.rs >> new file mode 100644 >> index 0000000000000000000000000000000000000000..ee0f67ad1a89e69f5f8d2077= eba5541b472e7d8a >> --- /dev/null >> +++ b/rust/kernel/num.rs >> @@ -0,0 +1,173 @@ >> +// SPDX-License-Identifier: GPL-2.0 >> + >> +//! Numerical and binary utilities for primitive types. >> + >> +use crate::build_assert; >> +use core::borrow::Borrow; >> +use core::fmt::Debug; >> +use core::hash::Hash; >> +use core::ops::Deref; >> + >> +/// An unsigned integer which is guaranteed to be a power of 2. >> +#[derive(Debug, Clone, Copy)] >> +#[repr(transparent)] >> +pub struct PowerOfTwo(T); >> + >> +macro_rules! power_of_two_impl { >> + ($($t:ty),+) =3D> { >> + $( >> + impl PowerOfTwo<$t> { >> + /// Validates that `v` is a power of two at build-time,= and returns it wrapped into >> + /// `PowerOfTwo`. >> + /// >> + /// A build error is triggered if `v` cannot be asserte= d to be a power of two. >> + /// >> + /// # Examples >> + /// >> + /// ``` >> + /// use kernel::num::PowerOfTwo; >> + /// >> + /// let v =3D PowerOfTwo::::new(256); >> + /// assert_eq!(v.value(), 256); >> + /// ``` >> + #[inline(always)] >> + pub const fn new(v: $t) -> Self { > > Then this function should be unsafe, because an invalid `v` can create > an invalid PowerOfTwo. Doesn't the `build_assert` below allow us to keep this method safe, since it will fail at build-time if it cannot be asserted that `v` is a power of two? > >> + build_assert!(v.count_ones() =3D=3D 1); >> + Self(v) >> + } >> + >> + /// Validates that `v` is a power of two at runtime, an= d returns it wrapped into >> + /// `PowerOfTwo`. >> + /// >> + /// `None` is returned if `v` was not a power of two. >> + /// >> + /// # Examples >> + /// >> + /// ``` >> + /// use kernel::num::PowerOfTwo; >> + /// >> + /// assert_eq!(PowerOfTwo::::try_new(16).unwrap().= value(), 16); >> + /// assert_eq!(PowerOfTwo::::try_new(15), None); >> + /// ``` >> + #[inline(always)] >> + pub const fn try_new(v: $t) -> Option { >> + match v.count_ones() { >> + 1 =3D> Some(Self(v)), >> + _ =3D> None, >> + } >> + } >> + >> + /// Returns the value of this instance. >> + /// >> + /// It is guaranteed to be a power of two. >> + /// >> + /// # Examples >> + /// >> + /// ``` >> + /// use kernel::num::PowerOfTwo; >> + /// >> + /// let v =3D PowerOfTwo::::new(256); >> + /// assert_eq!(v.value(), 256); >> + /// ``` >> + #[inline(always)] >> + pub const fn value(&self) -> $t { >> + self.0 >> + } >> + >> + /// Returns the mask corresponding to `self.value() - 1= `. >> + #[inline(always)] >> + pub const fn mask(&self) -> $t { >> + self.0.wrapping_sub(1) >> + } >> + >> + /// Aligns `self` down to `alignment`. >> + /// >> + /// # Examples >> + /// >> + /// ``` >> + /// use kernel::num::PowerOfTwo; >> + /// >> + /// assert_eq!(PowerOfTwo::::new(0x1000).align_dow= n(0x4fff), 0x4000); >> + /// ``` >> + #[inline(always)] >> + pub const fn align_down(self, value: $t) -> $t { > > I'm late to party, but could we instead implement: > > pub const fn round_down(value: i32, shift: i32) -> i32 { > value & !((1 << shift) - 1) > } > > pub const fn round_up(value: i32, shift: i32) -> i32 { > let mask =3D (1 << shift) - 1; > value.wrapping_add(mask) & !mask > } > > ? It's much harder to pass an invalid alignment with this. It also forces you to think in terms of shifts instead of values - i.e. you cannot round to `0x1000` as it commonly done in the kernel, now you need to do some mental gymnastics to know it is actually a shift of `12`. Being able to use the actual value to round to is more familiar (and natural) to me.