From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED8C9C433FE for ; Wed, 19 Oct 2022 11:03:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230312AbiJSLDp convert rfc822-to-8bit (ORCPT ); Wed, 19 Oct 2022 07:03:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35976 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234828AbiJSLDK (ORCPT ); Wed, 19 Oct 2022 07:03:10 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF045FA026 for ; Wed, 19 Oct 2022 03:32:35 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-306-19UG_-sFOqOSys9fWgfDtg-1; Wed, 19 Oct 2022 11:31:19 +0100 X-MC-Unique: 19UG_-sFOqOSys9fWgfDtg-1 Received: from AcuMS.Aculab.com (10.202.163.4) by AcuMS.aculab.com (10.202.163.4) with Microsoft SMTP Server (TLS) id 15.0.1497.42; Wed, 19 Oct 2022 11:31:17 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.042; Wed, 19 Oct 2022 11:31:17 +0100 From: David Laight To: 'Kang Minchul' , Greg Kroah-Hartman , Paulo Miguel Almeida CC: Dan Carpenter , Sidong Yang , "linux-staging@lists.linux.dev" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] staging: pi433: Use div64_u64 instead of do_div Thread-Topic: [PATCH] staging: pi433: Use div64_u64 instead of do_div Thread-Index: AQHY46M8g2A3zaXXyE2gPdBmwjkSwq4Vg27w Date: Wed, 19 Oct 2022 10:31:17 +0000 Message-ID: References: <20221019094015.832398-1-tegongkang@gmail.com> In-Reply-To: <20221019094015.832398-1-tegongkang@gmail.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kang Minchul > Sent: 19 October 2022 10:40 > > This commit removes warning generated by cocci as follows: > > do_div() does a 64-by-32 division, please consider using div64_u64 instead. > > Using div64_u64 instead of do_div can avoid potential truncation. Cocci is lying to you. do_div() exists because a 64 by 32 bit divide is significantly faster than a 64 by 64 divide. This is particularly true on 32bit cpu, but is also true on Intel x86_64 bit cpu. So unless the result might actually be larger than 32 bits (which requires code analysis) then do_div() is correct. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)