From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.2 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 223EE202A5 for ; Fri, 22 Sep 2017 16:05:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752148AbdIVQFG (ORCPT ); Fri, 22 Sep 2017 12:05:06 -0400 Received: from avasout07.plus.net ([84.93.230.235]:33911 "EHLO avasout07.plus.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751877AbdIVQFF (ORCPT ); Fri, 22 Sep 2017 12:05:05 -0400 Received: from [10.0.2.15] ([147.147.86.16]) by avasout07 with smtp id Cg531w0040M91Ur01g54jY; Fri, 22 Sep 2017 17:05:04 +0100 X-CM-Score: 0.00 X-CNFS-Analysis: v=2.2 cv=CrLPSjwD c=1 sm=1 tr=0 a=dubYQqM3tRRTmV8xSh8cXQ==:117 a=dubYQqM3tRRTmV8xSh8cXQ==:17 a=IkcTkHD0fZMA:10 a=vhG-M06Dpg7HnRSmaBMA:9 a=QEXdDO2ut3YA:10 X-AUTH: ramsayjones@:2500 Subject: Re: [PATCH 3/4] cache.h: hex2chr() - avoid -Wsign-compare warnings To: Jeff King Cc: Junio C Hamano , GIT Mailing-list References: <20170922054748.iseinawwwfw56vis@sigill.intra.peff.net> From: Ramsay Jones Message-ID: <89beb424-2cc0-bfe3-7847-c11035bfec70@ramsayjones.plus.com> Date: Fri, 22 Sep 2017 17:05:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20170922054748.iseinawwwfw56vis@sigill.intra.peff.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On 22/09/17 06:47, Jeff King wrote: > On Thu, Sep 21, 2017 at 05:48:38PM +0100, Ramsay Jones wrote: > >> diff --git a/cache.h b/cache.h >> index a916bc79e..a0e3e362c 100644 >> --- a/cache.h >> +++ b/cache.h >> @@ -1243,8 +1243,8 @@ static inline unsigned int hexval(unsigned char c) >> */ >> static inline int hex2chr(const char *s) >> { >> - int val = hexval(s[0]); >> - return (val < 0) ? val : (val << 4) | hexval(s[1]); >> + unsigned int val = hexval(s[0]); >> + return (val & ~0xf) ? val : (val << 4) | hexval(s[1]); >> } > > Ironically, the unsigned return from hexval() comes from internally > converting the signed char in hexval_table. And then we again return it > as a signed int from hex2chr(). Yep, my first inclination was to change the return type of hexval(), but after looking at all its callers, I decided against that (because it wouldn't help). ;-) > Would it make sense to return a signed int from hexval()? That would > make hex2chr just work as it tries to above. I admit that shifting > signed values is a little funny, but it should be fine here since we > know they're no larger than 8 bits in the first place. Indeed, shifting signed values is a no-no, which is why I decided to go this route. > As an aside, I also see some uses of hexval() that don't appear to be > quite as rigorous in checking for invalid characters. A few > unconditionally shift the first nibble and assume that there will still > be high bits set. I think that's generally true for twos-complement > negative numbers, but isn't shifting off the left side of a signed > integer undefined behavior? All uses of hexval() that I can see are shifting an unsigned value. Have I missed something? > And mailinfo's decode_q_segment() does not seem to check for errors at > all. Yes, I noticed that. (I put it on my TODO list). > Handling those is getting far off your original patch, but I'm having > trouble figuring out if it's saner for us to consistently stick to > all-signed or all-unsigned here. Oh, unsigned, without a doubt. :D ATB, Ramsay Jones