From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752493AbaAQKIF (ORCPT ); Fri, 17 Jan 2014 05:08:05 -0500 Received: from mx0.aculab.com ([213.249.233.131]:39710 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752471AbaAQKH5 (ORCPT ); Fri, 17 Jan 2014 05:07:57 -0500 From: David Laight To: "'Hannes Frederic Sowa'" , Christoph Lameter CC: Daniel Borkmann , "davem@davemloft.net" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Eric Dumazet , Austin S Hemmelgarn , "Jesse Gross" , Jamal Hadi Salim , "Stephen Hemminger" , Matt Mackall , "Pekka Enberg" , Andy Gospodarek , "Veaceslav Falico" , Jay Vosburgh , Jakub Zawadzki Subject: RE: [PATCH net-next 2/2] reciprocal_divide: correction/update of the algorithm Thread-Topic: [PATCH net-next 2/2] reciprocal_divide: correction/update of the algorithm Thread-Index: AQHPEt98Z7WBrBo+/0up6rnEAEb4SpqIsDOQ Date: Fri, 17 Jan 2014 10:05:37 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D45EB06@AcuExch.aculab.com> References: <1389828228-30312-1-git-send-email-dborkman@redhat.com> <1389828228-30312-3-git-send-email-dborkman@redhat.com> <20140116172406.GA17529@order.stressinduktion.org> In-Reply-To: <20140116172406.GA17529@order.stressinduktion.org> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id s0HA8FX9023755 From: Hannes Frederic Sowa > On Thu, Jan 16, 2014 at 10:37:37AM -0600, Christoph Lameter wrote: > > On Thu, 16 Jan 2014, Daniel Borkmann wrote: > > > > > - * or else the performance is slower than a normal divide. > > > - */ > > > -extern u32 reciprocal_value(u32 B); > > > +struct reciprocal_value { > > > + u32 m; > > > + u8 sh1, sh2; > > > +}; > > > > > > +#define RECIPROCAL_VALUE_RESULT_TO_ZERO ((struct reciprocal_value){.sh1 = 32}) > > > > > > -static inline u32 reciprocal_divide(u32 A, u32 R) > > > +struct reciprocal_value reciprocal_value(u32 d); > > > > A function that returns a struct? That works? Which gcc versions support > > it? > > Sure, that works and I actually like it. This is supported by the c standard, > but please don't ask me since which one. ;) I think it has always been supported. Originally by adding an extra hidden argument that points to an on-stack structure. More recent ABI tend to allow 'small' structures be returned in registers. (Typically ones that would fit in the register(s) used for an integral result). This doesn't mean that it is a good idea! OTOH if the function is 'static inline' (and inlined) it probably doesn't matter. David {.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I