Message-Id: <m10gpft-001mHUC@Dirac.Chemie.FU-Berlin.DE> From: melchers AT chemie DOT fu-berlin DOT de (Bernd Melchers) Subject: Re: Optimization question To: pgcc AT delorie DOT com Date: Mon, 10 May 1999 15:00:49 +0200 (MEST) In-Reply-To: <Pine.SOL.3.96.990510125208.12696D-100000@ursa.cus.cam.ac.uk> from "Dr H. T. Leung" at May 10, 99 01:07:16 pm X-Mailer: ELM [version 2.4 PL24 ME8d] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Reply-To: pgcc AT delorie DOT com X-Mailing-List: pgcc AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk 'Dr H. T. Leung wrote:' > > If you had read the mailing list archive, it is terribly unfair to people > on the list to cc you replies when you are not on the list. If you want to > ask a question, subscribe, read on for a while, then post (then maybe > unsubscribe). > > Your codes are very badly written (probably generated by automatic > symbolic algebra packages like reduce/mathematica?). An optimized compiler > can't help you much if your codes doesn't let itself be optimized. For a > very simple example, You were doing multipication "Pv1*v01" 4 times; that > means retrieves 2 values from memory, multiply, store it back, done 4 > times. Whereas you could have defined a new variable "Pv1_v01 = Pv1*v01", > then it is two retrievals, multiplication once, storage once, then > retrieval 4 times. You would be much better off spending some time good compilers should optimize such expressions by itself, the method is called "common subexpression optimization". Ciao Bernd -- Bernd Melchers | melchers AT FU-Berlin DOT DE Freie Universitaet Berlin | "We don't write software, we compose it." AG Macromolecular Modelling - Prof. Dr. E.W. Knapp for more information see http://userpage.chemie.fu-berlin.de/~melchers/