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Re: mktime() failures under PCTS testing
by eggert＠twinsun.com April 1, 1994

April 1, 1994

Mark Brader, who I believe is well connected with the C standardization process, wrote a news article about the mktime problem in which he indicated that he thought that mktime could yield -1 in the spring-forward gap (i.e. that this particular PCTS case is incorrect). I'll enclose a copy of the article at the end of this message. (It responds to another article that I don't have a copy of.) This is probably the best we can do until I get an official response to the C Standard defect report that I filed earlier this week. ----- Newsgroups: comp.std.c From: msb(a)sq.sq.com (Mark Brader) Subject: Re: Can mktime return -1 for times in the spring-forward gap? Message-ID: <1994Mar25.173447.2810(a)sq.sq.com> Summary: Yes, it's undefined behavior Organization: SoftQuad Inc., Toronto, Canada References: <Cn4tnp.DvM(a)twinsun.com> <2mr48c$duk(a)usenet.pa.dec.com> Date: Fri, 25 Mar 94 17:34:47 GMT The original question was about mktime() with the tm_isdst member negative, and times in the "spring-forward gap", i.e. the transition to Daylight Saving Time. > I think the standard contradicts itself. The relevant fields are not > restricted to the usual ranges, yet if the calendar time cannot be > represented then mktime returns -1. I think that your example requires > a return of -1, and an example with tm_hour being 27 is a calendar time > that cannot be represented so it requires a return of -1, even though > mktime has to force the fields into the usual ranges. I think that this is a strained interpretation, and that if a ruling was requested, the response would be that the standard is clear enough as it is. The intent of saying that "the original values ... are not restricted to the ranges indicated above" obviously was to allow alternative specifications for a calendar time, so that 27:00 UTC on October 15, 1982, would signify the same as 03:00 UTC on October 16, 1982; and I don't think there is any other reasonable way to read the actual text. > > The Rationale (section 4.12.2.3) clearly allows mktime to yield -1 in the > > ``fall-backward fold'' [i.e. the opposite transition]... > > The rationale conflicts with the standard, and the standard has priority. > If the tm_isdst field is -1, then a time in the "fall-backward fold" is a > calendar time that can be represented in two ways, so it can be represented, > so the return value cannot be -1 ... The Rationale for 4.12.2.3 does not specify what kind of behavior is involved here, but seems to mean that it is unspecified; perhaps that is what was intended. On reading 4.12.2.3/7.12.2.3 in the actual standard, though, I think the behavior is undefined. What it specifies is only that the broken-down time is converted to a calendar time value. For times in the gap and the fold, no well-defined conversion exists. Therefore, as I see it, the general exclusions in 1.6/3.16 and/or 4.1.6/7.1.7 apply, and the behavior is undefined. (And I think that's an unwise choice; I'd rather that it either be unspecified, or implementation-defined, or that -1 be returned.) > Perhaps now is the calendar time for a few more defect reports. Chuckle. I'd say so. > Every technical corrigendum is met by an equally troublesome new defect > report. But then again... -- Mark Brader, msb(a)sq.com | "You keep using that word. I do not think it means SoftQuad Inc., Toronto | what you think it means." -- The Princess Bride This article is in the public domain.

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Re: 18 sec
by Mills＠udel.edu March 31, 1994

March 31, 1994

Garrett, Wrong. See rfc1589 for an explanation. Dave

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tzcode94e.tar.gz
by ado March 31, 1994

March 31, 1994

The file "tzcode94e.tar.gz" is now available for anonymous ftp from the "~ftp/pub" directory of elsie.nci.nih.gov (128.231.16.1); "tzdata94d.tar.gz" remains the latest data file. The new code incorporates a change for the benefit of PCTS; diffs are attached. --ado SCCS/s.Makefile: 7.21 vs. 7.23 *** 7.21/Makefile Wed Mar 30 23:32:14 1994 --- 7.23/Makefile Wed Mar 30 23:32:15 1994 *************** *** 1,4 **** ! # @(#)Makefile 7.21 # Change the line below for your time zone (after finding the zone you want in # the time zone files, or adding it to a time zone file). --- 1,4 ---- ! # @(#)Makefile 7.23 # Change the line below for your time zone (after finding the zone you want in # the time zone files, or adding it to a time zone file). *************** *** 168,173 **** --- 168,179 ---- # -DCMUCS # to the end of the "CFLAGS=" line # This function is not described in X3J11's work. + # + # NIST-PCTS:151-2, Version 1.4, (1993-12-03) is a test suite put + # out by the National Institute of Standards and Technology + # which claims to test C and Posix conformance. If you want to pass PCTS, add + # -DPCTS + # to the end of the "CFLAGS=" line. CFLAGS= SCCS/s.localtime.c: 7.17 vs. 7.18 *** 7.17/localtime.c Wed Mar 30 23:32:17 1994 --- 7.18/localtime.c Wed Mar 30 23:32:18 1994 *************** *** 1,6 **** #ifndef lint #ifndef NOID ! static char elsieid[] = "@(#)localtime.c 7.17"; #endif /* !defined NOID */ #endif /* !defined lint */ --- 1,6 ---- #ifndef lint #ifndef NOID ! static char elsieid[] = "@(#)localtime.c 7.18"; #endif /* !defined NOID */ #endif /* !defined lint */ *************** *** 1308,1315 **** --- 1308,1326 ---- if (tmp->tm_isdst > 1) tmp->tm_isdst = 1; t = time2(tmp, funcp, offset, &okay); + #ifdef PCTS + /* + ** PCTS code courtesy Grant Sullivan (grant(a)osf.org) + */ + if (okay) + return t; + if (tmp->tm_isdst < 0) + tmp->tm_isdst = 0; /* reset to std and try again */ + #endif /* defined PCTS */ + #ifndef PCTS if (okay || tmp->tm_isdst < 0) return t; + #endif /* !defined PCTS */ /* ** We're supposed to assume that somebody took a time of one type ** and did some math on it that yielded a "struct tm" that's bad.

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18 sec
by Garrett Wollman March 29, 1994

March 29, 1994

<<On Tue, 29 Mar 1994 10:12:19 +0200 (MESZ), Hinrich Eilts <eilts(a)late.e-technik.uni-erlangen.de> said: > I synchronized FreeBSD-1.1-BETA to a stratum-1 timeserver by ntpdate > and xntpd and compared localtime by "date" with it and two other > machines, which are synchronized by xntpd too. FreeBSD has a > difference of -18 secounds to all other machines (a NeXT-Station > with NeXTStep, a Sun with SunOS 4.x and a HP9000-750 with > HPUX). What you are seeing is the interaction of several different `features' of NTP and FreeBSD. I'll try to explain, and again hope that somebody out there can provide a complete solution. Here are the problems... 1) The timezone database does not reflect the fact that the first time step, in going from GMT (pre-1972) to UTC (1972 to present) was actually 10 seconds, and not just one like all subsequent leap seconds. 2) The timezone database DOES include all subsequent time steps. 3) The NTP code ``handles'' leap seconds by turning the clock back when they happen. By contrast, the timezone code assumes that time_t's are increasing (which they ought to be; I hold that xntpd's behavior is simply wrong). To wit: NTP code wants: Real Time UNIX Time --------------- --------- --------- 30 June 1994, 23:59:59 t s 30 June 1994, 23:59:59 t+1 s 01 July 1994, 00:00:00 t+2 s+1 Timezone code wants: Real Time UNIX Time -------------------- --------- --------- 30 June 1994, 23:59:59 t s 30 June 1994, 23:59:60 t+1 s+1 01 July 1994, 00:00:00 t+2 s+2 A temporary (ugly hack) solution is to use `posix/your/time/zone' rather than `right/your/time/zone' (which is the same as `your/time/zone') for /etc/localtime. -GAWollman -- Garrett A. Wollman | Shashish is simple, it's discreet, it's brief. ... wollman(a)lcs.mit.edu | Shashish is the bonding of hearts in spite of distance. formerly known as | It is a bond more powerful than absence. We like people wollman(a)emba.uvm.edu | who like Shashish. - Claude McKenzie + Florent Vollant

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Re: 18 sec
by Bradley White March 29, 1994

March 29, 1994

Garrett Wollman <wollman(a)adrastea.lcs.mit.edu> writes: > What you are seeing is the interaction of several different `features' > of NTP and FreeBSD. I'll try to explain, and again hope that somebody > out there can provide a complete solution. Here is an encore of my reply of February 7th. --- Begin forwarded message Date: Mon, 07 Feb 1994 18:05:34 -0500 (EST) From: Bradley White <bww+(a)transarc.com> Subject: Re: leap seconds To: Garrett Wollman <wollman(a)emba.uvm.edu> Cc: Paul Eggert <eggert(a)twinsun.com>, Zone Watchers <tz(a)elsie.nci.nih.gov>, freebsd-tz(a)freefall.cdrom.com Message-Id: <09490.760662334(a)capitol.transarc.com> In-Reply-To: Your message of Mon, 7 Feb 94 17:23:21 -0500 <9402072223.AA23255(a)bajoran.emba.uvm.edu> Any system that runs with ``REDO=right_*'', and which therefore wants to continue to tick normally over leap seconds, needs to do a little bit of work to generate NTP-style timestamps. That is, NTP-style timestamps are discontinuous over leaps, while ``REDO=right_*'' time_t's are continuous. Recent incantations of the `tz' package provide the time2posix() function to help in mapping between these two formats. For example, in the (old, version-1) NTP code, you need to change ... stampp->int_part = htonl(tvp->tv_sec + JAN_1970); to stampp->int_part = htonl(time2posix(tvp->tv_sec) + JAN_1970); I haven't looked at the (new, version-3) XNTP code, but I imagine the change needed there is just as trivial. After that, you will chime NTP harmoniously with the rest of the world, *and*, you will sail smoothly through leap events without the jitter or confusion suffered by your NTP peers. Bradley

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AU Summer time channges (proposed).
by Robert Elz March 29, 1994

March 29, 1994

I'm not in AU right now, and haven't seen the announcementss, though there was talk of changes before I left, but I'm told there is agreement for Vic SA and Tas to switch to summer time on Oct 1, and revert to standard time Mar 31 to give exactly 6 months daylight saving (summer time really) a yearA. One would presume they'd keep the "change on a Sunday" rule, but who knows. Apparently NSW weren't impressed, but may end up changing their minds. I'm sure others in AU can give more details on this. kre

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Re: EU Summer Time update [forwarded with permission]
by ado March 29, 1994

March 29, 1994

> From @doc.memex.co.uk:peter@memex.co.uk Tue Mar 29 08:03:37 1994 > Return-Path: <@doc.memex.co.uk:peter@memex.co.uk> > Received: from relay2.UU.NET by elsie.nci.nih.gov (4.1/SMI-4.1) > id AA09181; Tue, 29 Mar 94 08:03:34 EST > Received: from young.cs.strath.ac.uk by relay2.UU.NET with SMTP > (5.61/UUNET-internet-primary) id AAwjia29244; Tue, 29 Mar 94 08:03:28 -0500 > Received: from doc.memex.co.uk by young.cs.strath.ac.uk id aa02542; > 29 Mar 94 14:02 +0100 > Received: by doc.memex.co.uk (4.1/memex_18) > id AA15065; Tue, 29 Mar 94 13:51:13 BST > Date: Tue, 29 Mar 94 13:51:13 BST > From: Peter Ilieve <peter(a)memex.co.uk> > Message-Id: <9403291251.AA15065(a)doc.memex.co.uk> > To: ado(a)elsie.nci.nih.gov > Subject: Re: EU Summer Time update > Status: RO > > > Thanks for the scoop on EU Summer Time. Is it premature to forward it to > > the time zone list? > > ... > > It is the best info available at present. My personal guess is that > nothing will be changed. I have no idea why it has taken since last > September to fail to confirm this directive, nor why it may take until > May. The first change from existing practice is not until October 95, > when the UK/Eire date is Sun>=22 rather than Sun>=23 so it is probably > safe to pass it on, even if you have to correct it later. > > > Peter

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EU Summer Time update [forwarded with permission]
by ado March 29, 1994

March 29, 1994

> From @doc.memex.co.uk:peter@memex.co.uk Mon Mar 28 04:36:25 1994 > Return-Path: <@doc.memex.co.uk:peter@memex.co.uk> > Received: from relay2.UU.NET by elsie.nci.nih.gov (4.1/SMI-4.1) > id AA12705; Mon, 28 Mar 94 04:36:22 EST > Received: from young.cs.strath.ac.uk by relay2.UU.NET with SMTP > (5.61/UUNET-internet-primary) id AAwjdu24981; Mon, 28 Mar 94 04:36:08 -0500 > Received: from doc.memex.co.uk by young.cs.strath.ac.uk id aa20721; > 28 Mar 94 10:34 +0100 > Received: by doc.memex.co.uk (4.1/memex_18) > id AA05804; Mon, 28 Mar 94 10:32:19 BST > Date: Mon, 28 Mar 94 10:32:19 BST > From: Peter Ilieve <peter(a)memex.co.uk> > Message-Id: <9403280932.AA05804(a)doc.memex.co.uk> > To: ado(a)elsie.nci.nih.gov > Subject: EU Summer Time update > Status: RO > > I now have a copy of the proposal for the 7th EC directive on summer time > arrangements (COM (93) 439 final, 27 September 1993). This is not yet > a formal directive, treat this as advance warning, some dates may still > change. > > I what looks like a triumph of British obduracy over the poor benighted > foreigners it is proposed to move to a common end date of the 4th Sunday > in October from 1997 so the foreigners will have their winter benightment > postponed by a month. The EC Commission actually asked its tame polling > organisation to conduct one of its Eurobarometer surveys which showed > `that European public opinion is very much in favour of having summer > time extended until the end of October'. > > The dates proposed are: > > 1995: last Sunday in March (26 March) to last Sunday in September (24 Sep) > (UK & Eire ending on 4th Sunday in October (22 Oct)) > 1996: last Sunday in March (31 March) to last Sunday in September (29 Sep) > (UK & Eire ending on 4th Sunday in October (27 Oct)) > 1997: last Sunday in March (30 March) to 4th Sunday in October (26 Oct) > 1998: last Sunday in March (29 March) to 4th Sunday in October (25 Oct) > > The UK/Eire end date of 22 October conflicts with your current rule of > Oct Sun>=23, and the historical UK formula of Sun after 4th Sat. The > last time 4th Sun and Sun after 4th Sat differed was in 1989, when 29 > October was used. That year was covered by a UK Summer Time Order for > only a single year and it looks as though there was a matching 4th EC > directive for just this year. I don't have the text of the 5th EC > directive (for 1990--92) but my guess would be it said 4th Sun. To > maintain strict historical accuracy you could start a new UK ending > rule of Oct Sun>=22 in 1990. A similar rule will be needed for all the > -Eur rules from 1997. > > Negotiations about joinging the EU have been concluded with Austria, > Finland, Norway and Sweden and if the current argument among the existing > members about consequential changes in voting rules can be resolved > they should join on 1 Jan 1995, and will presumably use the same > summer time rules as the existing members. I don't know what they do now. > > As I said, this is only a proposal at present. The EC information office > in Edinburgh could give a guesstimate of when the final version might > emerge. The Home Office guessed at the end of May. > I will keep you posted. > > > Peter Ilieve peter(a)memex.co.uk

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Re: mktime() failures under PCTS testing
by Grant Sullivan March 23, 1994

March 23, 1994

In PCTS, "ambiguous" is referring to the time periods at, and 59:59 minutes after the start of daylight savings, where the time given is as if there were no transition to daylight savings 59:59 minutes before, and at the end of daylight savings, where the time given is as if there were no transition from daylight savings and tm_isdst = -1, assuming the difference between standard vs. daylight is 60:00 minutes. I've run tests on SVR4v3 and HP-UX C.09.01 systems and found their mktime() maps 02:MM:SS/DST-UNKNOWN to 01:MM:SS/DST-OFF I think I prefer 02:MM:SS/DST-UNKNOWN to 03:MM:SS/DST-ON but either mapping is acceptable to PCTS. ------- Forwarded Message Return-Path: bww+(a)transarc.com Received: from sparc51.transarc.com (sparc51.transarc.com, [192.55.207.51]) by transarc.com (5.54/3.15) id <AA06638> for grant(a)osf.org; Wed, 23 Mar 94 14:51:15 EST Received: by sparc51.transarc.com with BradMail(MH 6.8); Wed, 23 Mar 1994 14:51:06 -0500 (EST) To: Grant Sullivan <grant(a)osf.org> Cc: Arthur David Olson <ado(a)elsie.nci.nih.gov> Subject: Re: mktime() failures under PCTS testing In-Reply-To: Your message of Wed, 23 Mar 1994 13:37:01 -0500 Date: Wed, 23 Mar 1994 14:51:05 -0500 (EST) Message-Id: <16001.764452265(a)sparc51.transarc.com> From: Bradley White <bww+(a)transarc.com> > mktime() is failing only those PCTS tests which test "ambiguous" transitions > from standard to daylight time. mktime() passes all the tests for "ambiguous" > transitions from daylight to standard time, however. The first and second senses of the word "ambiguous" should be distinguished. The daylight->standard transition period does indeed include wall-clock times that each correspond to two distinct time_t's. However, the standard->daylight transition period renders wall-clock times that simply do not exist. And now my opinion: I am all for mktime() failing for *all* non-existent times-of-day, but, given that we do `isdst' correction, and map the non-existent times of ... 02:MM:SS/DST-OFF to 03:MM:SS/DST-ON and 02:MM:SS/DST-ON to 01:MM:SS/DST-OFF ..., it seems that we should also map 02:MM:SS/DST-UNKNOWN to one of those. Bradley PS: I won't mention that the test suite assumes too much about time_t's :-). ------- End of Forwarded Message

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Re: mktime() failures under PCTS testing
by ado March 23, 1994

March 23, 1994

The ftpable-from-elsie version of the time zone code suffers the same fate as related by grant@osf; on our SunOS 4.1.1 system, after making this change to the sample code: > SCCS/s.try.c: 1.1 vs. 1.2 > *** 1.1/try.c Tue Mar 22 18:45:08 1994 > --- 1.2/try.c Tue Mar 22 18:45:08 1994 > *************** > *** 34,43 **** > --- 34,53 ---- > printf("mktime test: for this test, set TZ=dst0std,J057,J059\n"); > printf("current value of TZ = %s\n", getenv("TZ")); > > + #if 0 > if (setenv("TZ", TZ_value, 1) != 0) { > printf("resetting TZ failed\n"); > exit(1); > } > + #else > + { > + char buf[512]; > + > + (void) strcpy(buf, "TZ="); > + (void) strcat(buf, TZ_value); > + putenv(buf); > + } > + #endif > printf("new value of TZ = %s\n", getenv("TZ")); > > time_str.tm_year = TM_year - 1900; ...I get these results: > mktime test: PCTS/STD/LS/mktime 8.1.58_9 Assert 5.1.3 > mktime test: for this test, set TZ=dst0std,J057,J059 > current value of TZ = (null) > new value of TZ = std0dst,J057,J059 > time_str tm struct set to: > year = 91, mon = 1, mday = 26, hour = 2, min = 0, sec = 0, wday = -1, yday = -1, isdst = -1 > expected value from mktime = 667530000 >>>>> mktime returned -1 (-unknown-) > mktime() final time_str tm struct reset to: > year = 91, mon = 1, mday = 26, hour = 2, min = 0, sec = 0, wday = -1, yday = -1, isdst = -1 Vintage time zone hands will recognize this as behavior that certain SunOS versions of the "cron" program clashed with. The time zone package is assuming that the "mktime" call is asking a question such as... If US DST rules are in effect and I'm in the Eastern US, when, on April 3, 1994, will a wall clock show 2:30 a.m. (irrespective of whether it is or isn't daylight saving time)? ...and the "-1" answer is the package's way of saying... There is no such time! If someone has the relevant wording from the current version of the relevant standard(s) on what to do here, I'd love to hear from you. --ado

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