From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754346AbbAVXQJ (ORCPT ); Thu, 22 Jan 2015 18:16:09 -0500 Received: from bh-25.webhostbox.net ([208.91.199.152]:41546 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752992AbbAVXQG (ORCPT ); Thu, 22 Jan 2015 18:16:06 -0500 Message-ID: <54C184B0.7060606@roeck-us.net> Date: Thu, 22 Jan 2015 15:16:00 -0800 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Rasmus Villemoes , Jean Delvare CC: lm-sensors@lm-sensors.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] drivers/hwmon/ad7314.c: Do proper sign extension References: <1421966655-16188-1-git-send-email-linux@rasmusvillemoes.dk> In-Reply-To: <1421966655-16188-1-git-send-email-linux@rasmusvillemoes.dk> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-CTCH-PVer: 0000001 X-CTCH-Spam: Unknown X-CTCH-VOD: Unknown X-CTCH-Flags: 0 X-CTCH-RefID: str=0001.0A020204.54C184B3.011D,ss=1,re=0.001,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0 X-CTCH-Score: 0.001 X-CTCH-ScoreCust: 0.000 X-CTCH-Rules: C_4847, X-CTCH-SenderID: linux@roeck-us.net X-CTCH-SenderID-Flags: 0 X-CTCH-SenderID-TotalMessages: 1 X-CTCH-SenderID-TotalSpam: 0 X-CTCH-SenderID-TotalSuspected: 0 X-CTCH-SenderID-TotalConfirmed: 0 X-CTCH-SenderID-TotalBulk: 0 X-CTCH-SenderID-TotalVirus: 0 X-CTCH-SenderID-TotalRecipients: 0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: mailgid no entry from get_relayhosts_entry X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/22/2015 02:44 PM, Rasmus Villemoes wrote: > The comment above (data << 2) >> 2 explains what the intention is: To > use bit 13 of the 14-bit value data as the sign bit. However, this > doesn't work due to C's promotion rules. data has type s16, but data > << 2 has type int. To get sign extension, that expression would have > to be cast back to an s16 before being shifted (at which point C's > promotion rules would then kick in again and promote the left operand > to int). As it stands, both expressions are no-ops for any value of > data. > > Avoid these subtleties by using the existing API for > this. sign_extend32 works equally well for 8 and 16 bit types. > > Signed-off-by: Rasmus Villemoes > --- Good catch. Applied. Thanks, Guenter