From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754205Ab2IIQRu (ORCPT ); Sun, 9 Sep 2012 12:17:50 -0400 Received: from mail.active-venture.com ([67.228.131.205]:58346 "EHLO mail.active-venture.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751075Ab2IIQRs (ORCPT ); Sun, 9 Sep 2012 12:17:48 -0400 X-Originating-IP: 108.223.40.66 Date: Sun, 9 Sep 2012 09:17:59 -0700 From: Guenter Roeck To: Geert Uytterhoeven Cc: linux-kernel@vger.kernel.org, Andrew Morton , Pekka Enberg , Ingo Molnar , "H. Peter Anvin" , Jean Delvare , lm-sensors@lm-sensors.org Subject: Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends Message-ID: <20120909161759.GA7998@roeck-us.net> References: <1346425339-17138-1-git-send-email-linux@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 09, 2012 at 04:57:34PM +0200, Geert Uytterhoeven wrote: > On Fri, Aug 31, 2012 at 5:02 PM, Guenter Roeck wrote: > > DIV_ROUND_CLOSEST returns a bad result for negative dividends: > > DIV_ROUND_CLOSEST(-2, 2) = 0 > > > > Most of the time this does not matter. However, in the hardware monitoring > > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be > > negative (such as temperatures). > > This seems to cause 3 new warnings in my m68k builds of v3.6-rc5: > > drivers/hwmon/mcp3021.c:76: warning: comparison is always true due to > limited range of data type > drivers/ide/ide-cd.c:1158: warning: comparison is always true due to > limited range of data type > drivers/ide/ide-cd.c:1159: warning: comparison is always true due to > limited range of data type > > $ m68k-linux-gnu-gcc -v > Using built-in specs. > Target: m68k-linux-gnu > Configured with: ../src/configure -v --enable-languages=c,c++ > --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib > --without-included-gettext --enable-threads=posix --enable-nls > --with-gxx-include-dir=/usr/m68k-linux-gnu/include/c++/4.1.2 > --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu > --enable-libstdcxx-debug --disable-libssp --disable-werror > --enable-checking=release --program-prefix=m68k-linux-gnu- > --includedir=/usr/m68k-linux-gnu/include --build=x86_64-linux-gnu > --host=x86_64-linux-gnu --target=m68k-linux-gnu > Thread model: posix > gcc version 4.1.2 20061115 (prerelease) (Ubuntu 4.1.1-21) > Hi Gert, The "always true" condition is on purpose to cause the compiler to optimize the expression away. I don't see the warnings myself, on none of the targets I am building (x86, ppc, arm, mips), but then I am using much more recent compiler versions. Odd is that you only see the warnings on "u16" and not elsewhere. I don't immediately see the warnings with a more recent m68k compiler (4.6.3), nor with any other target (x86, ppc, arm, mips) in my nightly builds. Can you send me your configuration ? Also, do you know where I can find the Ubuntu/Debian package for your compiler version, by any chance ? Thanks, Guenter