From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/13109 Path: news.gmane.org!.POSTED!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH] strftime: fix %z sign for small negative time zone offsets Date: Tue, 7 Aug 2018 22:14:58 -0400 Message-ID: <20180808021458.GB1878@brightrain.aerifal.cx> References: <20180725101142.29159-1-zajec5@gmail.com> <20180802232923.GO1392@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: blaine.gmane.org 1533694392 30667 195.159.176.226 (8 Aug 2018 02:13:12 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 8 Aug 2018 02:13:12 +0000 (UTC) User-Agent: Mutt/1.5.21 (2010-09-15) To: musl@lists.openwall.com Original-X-From: musl-return-13125-gllmg-musl=m.gmane.org@lists.openwall.com Wed Aug 08 04:13:08 2018 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.84_2) (envelope-from ) id 1fnDyF-0007pp-5I for gllmg-musl@m.gmane.org; Wed, 08 Aug 2018 04:13:07 +0200 Original-Received: (qmail 20028 invoked by uid 550); 8 Aug 2018 02:15:12 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 19999 invoked from network); 8 Aug 2018 02:15:11 -0000 Content-Disposition: inline In-Reply-To: <20180802232923.GO1392@brightrain.aerifal.cx> Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:13109 Archived-At: On Thu, Aug 02, 2018 at 07:29:23PM -0400, Rich Felker wrote: > On Wed, Jul 25, 2018 at 12:11:42PM +0200, Rafał Miłecki wrote: > > From: Rafał Miłecki > > > > Using + printf flag for printing plus/minus sign isn't reliable for > > negative offsets greater than -3600. In such cases the first two digits > > are zero but offset still should be printed with a leading minus char. > > > > Existing implementation results in code: > > struct tm tm = { .tm_gmtoff = -1800, }; > > char buf[255]; > > strftime(buf, sizeof(buf), "%z", &tm); > > puts(buf); > > printing +0030 instead of -0030. > > > > This patch fixes it by handling sign character manually and checking the > > __tm_gmtoff value (instead of __tm_gmtoff / 3600). > > > > Signed-off-by: Rafał Miłecki > > --- > > src/time/strftime.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/src/time/strftime.c b/src/time/strftime.c > > index 0a256970..6716ad4b 100644 > > --- a/src/time/strftime.c > > +++ b/src/time/strftime.c > > @@ -181,7 +181,8 @@ const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm * > > *l = 0; > > return ""; > > } > > - *l = snprintf(*s, sizeof *s, "%+.2ld%.2d", > > + *l = snprintf(*s, sizeof *s, "%c%.2ld%.2d", > > + tm->__tm_gmtoff >= 0 ? '+' : '-', > > (tm->__tm_gmtoff)/3600, > > abs(tm->__tm_gmtoff%3600)/60); > > return *s; > > -- > > I think this is incorrect. tm->__tm_gmtoff/3600 can still be negative, > and then the - sign is printed twice. > > I suspect your patch is correct if we add abs() around that expression > too, but maybe it makes more sense to assemble the value to be printed > as a single integer: > > tm->__tm_gmtoff/3600*100 + tm->__tm_gmtoff%3600/60 > > I didn't spend a lot of time working out that this is correct, but it > looks right and checks out with a few test cases. I've thrown various values at it and it seems to work fine, so I'll commit this version. Rich