Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 14 Mar 2002 07:53:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 14 Mar 2002 07:53:05 -0500 Received: from dsl-213-023-038-002.arcor-ip.net ([213.23.38.2]:33953 "EHLO starship") by vger.kernel.org with ESMTP id ; Thu, 14 Mar 2002 07:52:53 -0500 Content-Type: text/plain; charset=US-ASCII From: Daniel Phillips To: root@chaos.analogic.com, wli@holomorphy.com Subject: Re: 2.4.19pre2aa1 Date: Thu, 14 Mar 2002 13:47:19 +0100 X-Mailer: KMail [version 1.3.2] Cc: Andrea Arcangeli , wli@parcelfarce.linux.theplanet.co.uk, linux-kernel@vger.kernel.org, riel@surriel.com, hch@infradead.org, phillips@bonn-fries.net In-Reply-To: In-Reply-To: MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Message-Id: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On March 14, 2002 01:18 pm, Richard B. Johnson wrote: > On Wed, 13 Mar 2002 wli@holomorphy.com wrote: > > [big swinging math stuff] > > Listen you incompetent amoeba. I attempted to tell you in a nice > way that your apparent mastery of technical mumbo-jumbo will be > detected by many who have actual knowledge and expertise in the > area in which you pretend to be competent. You were way wide of the mark, though admittedly Bill reacted more agressively than necessary, it's what happens when you use steroids to build up your math muscles ;-) Bill knows what a pseudorandom generator is, and how to use it for testing hash functions, so do I. I don't really like the one you showed, though I appeciate the fact it's a couple of assembly instructions and has a decent period. Did you run a spectral test[1] on it? I'd be surprised if the results are pretty, though pleasantly surprised. I have one myself sitting around somewhere that's 2 or 3 instructions long, based on an LSR, which does have some analyzable properties. Though for serious testing I wouldn't use it - I'd crack my Numerical Recipes in C or use urandom, taking it on faith that the coder was duly diligent. A few cycles saved evaluating the hash just isn't worth it if you then have to wonder if patterns in your generator are showing through to your test results. You missed a lot if you didn't notice the quality of Bill's work on the hash. I 100% agree with his approach[2]. The fact he managed to satisfy davem should tell you a lot - we now have nice, short multiplicative hashes to use that get evaluated as fast shift-adds on sparc. These hashes have *provably* good behavior. Thanks Bill. [1] see Knuth [2] well, I sort of put him up to it... -- Daniel - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/