Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422679AbXBHXh4 (ORCPT ); Thu, 8 Feb 2007 18:37:56 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422709AbXBHXhz (ORCPT ); Thu, 8 Feb 2007 18:37:55 -0500 Received: from smtp.osdl.org ([65.172.181.24]:45419 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422679AbXBHXhy (ORCPT ); Thu, 8 Feb 2007 18:37:54 -0500 Date: Thu, 8 Feb 2007 15:37:38 -0800 (PST) From: Linus Torvalds To: David Rientjes cc: Jan Engelhardt , Jeff Garzik , Linux Kernel Mailing List , Andrew Morton Subject: Re: somebody dropped a (warning) bomb In-Reply-To: Message-ID: References: <45CB3B28.60102@garzik.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1720 Lines: 50 On Thu, 8 Feb 2007, David Rientjes wrote: > > And a compiler that makes a_variable.flag unsigned would be brain-dead > because "int" is always signed. No, making bitfields unsigned is actually usually a good idea. It allows you to often generate better code, and it actually tends to be what programmers _expect_. A lot of people seem to be surprised to hear that a one-bit bitfield actually often encodes -1/0, and not 0/1. So unsigned bitfields are not only traditional K&R, they are also usually _faster_ (which is probably why they are traditional K&R - along with allowing "char" to be unsigned by default). Don't knock them. It's much better to just remember that bitfields simply don't _have_ any standard sign unless you specify it explicitly, than saying "it should be signed because 'int' is signed". I will actually argue that having signed bit-fields is almost always a bug, and that as a result you should _never_ use "int" at all. Especially as you might as well just write it as signed a:1; if you really want a signed bitfield. So I would reall yrecommend that you never use "int a:" AT ALL, because there really is never any good reason to do so. Do it as unsigned a:3; signed b:2; but never int c:4; because the latter really isn't sensible. "sparse" will actually complain about single-bit signed bitfields, and it found a number of cases where people used that "int x:1" kind of syntax. Just don't do it. Linus - 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/