From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751411AbXCHDOm (ORCPT ); Wed, 7 Mar 2007 22:14:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751400AbXCHDOm (ORCPT ); Wed, 7 Mar 2007 22:14:42 -0500 Received: from smtp.osdl.org ([65.172.181.24]:45732 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751376AbXCHDOk (ORCPT ); Wed, 7 Mar 2007 22:14:40 -0500 Message-ID: <45EF7EB7.8040806@linux-foundation.org> Date: Wed, 07 Mar 2007 19:10:47 -0800 From: Stephen Hemminger Organization: Linux Foundation User-Agent: Thunderbird 1.5.0.10 (Windows/20070221) MIME-Version: 1.0 To: David Miller CC: w@1wt.eu, rkuhn@e18.physik.tu-muenchen.de, andi@firstfloor.org, dada1@cosmosbay.com, jengelh@linux01.gwdg.de, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH] tcp_cubic: use 32 bit math References: <20070306145842.7d7fea84@freekitty> <20070307060838.GI943@1wt.eu> <20070307170731.2b4397e3@freekitty> <20070307.185539.48527371.davem@davemloft.net> In-Reply-To: <20070307.185539.48527371.davem@davemloft.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org David Miller wrote: > From: Stephen Hemminger > Date: Wed, 7 Mar 2007 17:07:31 -0800 > > >> The basic calculation has to be done in 32 bits to avoid >> doing 64 bit divide by 3. The value x is only 22bits max >> so only need full 64 bits only for x^2. >> >> Signed-off-by: Stephen Hemminger >> > > Applied, thanks Stephen. > > What about Willy Tarreau's supposedly even faster variant? > Or does this incorporate that set of improvements? > That's what this is: x = (2 * x + (uint32_t)div64_64(a, (uint64_t)x*(uint64_t)x)) / 3;