Improve the support for perpetual DST.

Problem reported by Zefram in
<http://mm.icann.org/pipermail/tz/2013-September/020059.html>.
* localtime.c (tzparse): Elide simultaneous entries out of and
into DST if DST goes for an hour more than a year (actually, for
more than the DST offset more than a year).  Since this
optimization can elide all entries, avoid looping forever looking
for entries that will never arrive.  While we're at it, fix
another portability bug where the code assumed wraparound on
signed integer overflow.
* newtzset.3, tzfile.5: Mention that as an extension to POSIX,
if DST covers the entire year plus the DST offset, it's assumed to
be in effect all year.  Give an example.
* zic.c (stringrule): Omit the "J" in January and February,
as this can save a byte or two in the output.
(rule_cmp): New function.
(stringzone): Do a better job of constructing the standard-time
abbreviation when there is perpetual DST.  Defer to the new
stringrule to construct the times for perpetual DST.
Fix bug noted by Zefram, which caused a stray hour of standard
time to be inserted in an otherwise perpetual DST.
Previously, this code generated "WARST4WARST,J1/0,J365/24"
for the San Luis example; now it generates "WART4WARST,0/0,J365/25".

localtime.c

@@ -1008,6 +1008,7 @@ tzparse(const char *name, register struct state *const sp,
 			struct rule	start;
 			struct rule	end;
 			register int	year;
+			register int	yearlim;
 			register time_t	janfirst;
 			time_t		starttime;
 			time_t		endtime;
@@ -1035,16 +1036,24 @@ tzparse(const char *name, register struct state *const sp,
 			atp = sp->ats;
 			typep = sp->types;
 			janfirst = 0;
-			sp->timecnt = 0;
-			for (year = EPOCH_YEAR;
-			    sp->timecnt + 2 <= TZ_MAX_TIMES;
-			    ++year) {
-			    	time_t	newfirst;
+			yearlim = EPOCH_YEAR + YEARSPERREPEAT;
+			for (year = EPOCH_YEAR; year < yearlim; year++) {
+				int_fast32_t yearsecs;
 
 				starttime = transtime(janfirst, year, &start,
 					stdoffset);
 				endtime = transtime(janfirst, year, &end,
 					dstoffset);
+				yearsecs = (year_lengths[isleap(year)]
+					    * SECSPERDAY);
+				if (starttime > endtime
+				    || (starttime < endtime
+					&& (endtime - starttime
+					    < (yearsecs
+					       + (stdoffset - dstoffset))))) {
+					if (&sp->ats[TZ_MAX_TIMES - 2] < atp)
+						break;
+					yearlim = year + YEARSPERREPEAT + 1;
 					if (starttime > endtime) {
 						*atp++ = endtime;
 						*typep++ = 1;	/* DST ends */
@@ -1056,14 +1065,14 @@ tzparse(const char *name, register struct state *const sp,
 						*atp++ = endtime;
 						*typep++ = 1;	/* DST ends */
 					}
-				sp->timecnt += 2;
-				newfirst = janfirst;
-				newfirst += year_lengths[isleap(year)] *
-					SECSPERDAY;
-				if (newfirst <= janfirst)
-					break;
-				janfirst = newfirst;
 				}
+				if (time_t_max - janfirst < yearsecs)
+					break;
+				janfirst += yearsecs;
+			}
+			sp->timecnt = atp - sp->ats;
+			if (!sp->timecnt)
+				sp->typecnt = 1;	/* Perpetual DST.  */
 		} else {
 			register int_fast32_t	theirstdoffset;
 			register int_fast32_t	theirdstoffset;

newtzset.3

@@ -132,6 +132,10 @@ describes when the change back happens.  Each
 .I time
 field describes when, in current local time, the change to the other
 time is made.
+As an extension to POSIX, daylight saving is assumed to be in effect
+all year if it begins January 1 at 00:00 and ends December 31 at
+24:00 plus the difference between daylight saving and standard time,
+leaving no room for standard time in the calendar.
 .IP
 The format of
 .I date
@@ -183,7 +187,7 @@ or
 .RB `` \(pl '').
 As an extension to POSIX, the hours part of
 .I time
-can range from \(mi167 to 167; this allows for unusual rules such
+can range from \(mi167 through 167; this allows for unusual rules such
 as "the Saturday before the first Sunday of March".  The default, if
 .I time
 is not given, is
@@ -212,6 +216,16 @@ stands for Israel standard time (IST) and Israel daylight time (IDT),
 fourth Thursday in March (i.e., 02:00 on the first Friday on or after
 March 23), and fall back at 02:00 on the last Sunday in October.
 .TP
+.B WART4WARST,J1/0,J365/25
+stands for Western Argentina Summer Time (WARST), 3 hours behind UTC.
+There is a dummy transition to standard time on December 31 at 25:00
+daylight saving time (i.e., 24:00 standard time, equivalent to January
+1 at 00:00 standard time), and a simultaneous transition to daylight
+saving time on January 1 at 00:00 standard time, so daylight saving
+time is in effect all year and the initial
+.B WART
+is a placeholder.
+.TP
 .B WGT3WGST,M3.5.0/\(mi2,M10.5.0/\(mi1
 stands for Western Greenland Time (WGT) and Western Greenland Summer
 Time (WGST), 3 hours behind UTC, where clocks follow the EU rules of

tzfile.5

@@ -145,10 +145,14 @@ POSIX-TZ-environment-variable-style string for use in handling instants
 after the last transition time stored in the file
 (with nothing between the newlines if there is no POSIX representation for
 such instants).
-This string may use a minor extension to the POSIX TZ format: the
-hours part of its transition times may be signed and range from
+As described in
+.IR newtzset (3),
+this string may use two minor extensions to the POSIX TZ format.
+First, the hours part of its transition times may be signed and range from
 \(mi167 through 167 instead of the POSIX-required unsigned values
-from 0 through 24.
+from 0 through 24.  Second, DST is in effect all year if it starts
+January 1 at 00:00 and ends December 31 at 24:00 plus the difference
+between daylight saving and standard time.
 .SH SEE ALSO
 newctime(3), newtzset(3)
 .\" This file is in the public domain, so clarified as of

zic.c

@@ -1804,6 +1804,10 @@ stringrule(char *result, const struct rule *const rp, const zic_t dstoff,
 		total = 0;
 		for (month = 0; month < rp->r_month; ++month)
 			total += len_months[0][month];
+		/* Omit the "J" in Jan and Feb, as that's shorter.  */
+		if (rp->r_month <= 1)
+		  (void) sprintf(result, "%d", total + rp->r_dayofmonth - 1);
+		else
 		  (void) sprintf(result, "J%d", total + rp->r_dayofmonth);
 	} else {
 		register int	week;
@@ -1842,6 +1846,20 @@ stringrule(char *result, const struct rule *const rp, const zic_t dstoff,
 	return 0;
 }
 
+static int
+rule_cmp(struct rule const *a, struct rule const *b)
+{
+	if (!a)
+		return -!!b;
+	if (!b)
+		return 1;
+	if (a->r_hiyear != b->r_hiyear)
+		return a->r_hiyear < b->r_hiyear ? -1 : 1;
+	if (a->r_month - b->r_month != 0)
+		return a->r_month - b->r_month;
+	return a->r_dayofmonth - b->r_dayofmonth;
+}
+
 static void
 stringzone(char *result, const struct zone *const zpfirst, const int zonecount)
 {
@@ -1851,6 +1869,7 @@ stringzone(char *result, const struct zone *const zpfirst, const int zonecount)
 	register struct rule *		dstrp;
 	register int			i;
 	register const char *		abbrvar;
+	struct rule			stdr, dstr;
 
 	result[0] = '\0';
 	zp = zpfirst + zonecount - 1;
@@ -1874,19 +1893,17 @@ stringzone(char *result, const struct zone *const zpfirst, const int zonecount)
 	if (stdrp == NULL && dstrp == NULL) {
 		/*
 		** There are no rules running through "max".
-		** Let's find the latest rule.
+		** Find the latest std rule in stdabbrrp
+		** and latest rule of any type in stdrp.
 		*/
+		register struct rule *stdabbrrp = NULL;
 		for (i = 0; i < zp->z_nrules; ++i) {
 			rp = &zp->z_rules[i];
-			if (stdrp == NULL || rp->r_hiyear > stdrp->r_hiyear ||
-				(rp->r_hiyear == stdrp->r_hiyear &&
-				(rp->r_month > stdrp->r_month ||
-				(rp->r_month == stdrp->r_month &&
-				rp->r_dayofmonth > stdrp->r_dayofmonth))))
+			if (rp->r_stdoff == 0 && rule_cmp(stdabbrrp, rp) < 0)
+				stdabbrrp = rp;
+			if (rule_cmp(stdrp, rp) < 0)
 				stdrp = rp;
 		}
-		if (stdrp != NULL && stdrp->r_stdoff != 0)
-			dstrp = stdrp; /* We end up in DST.  */
 		/*
 		** Horrid special case: if year is 2037,
 		** presume this is a zone handled on a year-by-year basis;
@@ -1894,6 +1911,27 @@ stringzone(char *result, const struct zone *const zpfirst, const int zonecount)
 		*/
 		if (stdrp != NULL && stdrp->r_hiyear == 2037)
 			return;
+
+		if (stdrp != NULL && stdrp->r_stdoff != 0) {
+			/* Perpetual DST.  */
+			dstr.r_month = TM_JANUARY;
+			dstr.r_dycode = DC_DOM;
+			dstr.r_dayofmonth = 1;
+			dstr.r_tod = 0;
+			dstr.r_todisstd = dstr.r_todisgmt = FALSE;
+			dstr.r_stdoff = stdrp->r_stdoff;
+			dstr.r_abbrvar = stdrp->r_abbrvar;
+			stdr.r_month = TM_DECEMBER;
+			stdr.r_dycode = DC_DOM;
+			stdr.r_dayofmonth = 31;
+			stdr.r_tod = SECSPERDAY + stdrp->r_stdoff;
+			stdr.r_todisstd = stdr.r_todisgmt = FALSE;
+			stdr.r_stdoff = 0;
+			stdr.r_abbrvar
+			  = (stdabbrrp ? stdabbrrp->r_abbrvar : "");
+			dstrp = &dstr;
+			stdrp = &stdr;
+		}
 	}
 	if (stdrp == NULL && (zp->z_nrules != 0 || zp->z_stdoff != 0))
 		return;
@@ -1913,16 +1951,12 @@ stringzone(char *result, const struct zone *const zpfirst, const int zonecount)
 				return;
 		}
 	(void) strcat(result, ",");
-	if (dstrp == stdrp)
-		(void) strcat(result, "J1/0");
-	else if (stringrule(result, dstrp, dstrp->r_stdoff, zp->z_gmtoff) != 0) {
+	if (stringrule(result, dstrp, dstrp->r_stdoff, zp->z_gmtoff) != 0) {
 		result[0] = '\0';
 		return;
 	}
 	(void) strcat(result, ",");
-	if (dstrp == stdrp)
-		(void) strcat(result, "J365/24");
-	else if (stringrule(result, stdrp, dstrp->r_stdoff, zp->z_gmtoff) != 0) {
+	if (stringrule(result, stdrp, dstrp->r_stdoff, zp->z_gmtoff) != 0) {
 		result[0] = '\0';
 		return;
 	}