Import tzcode 2026d

2026-10-28 11:25:21 +01:00 · 2026-09-13 15:18:34 +02:00
1 parent 2479b6921a
commit 4d4fdb78db
@@ -22,7 +22,7 @@ To email small changes, please run a POSIX shell command like
 For more-elaborate or possibly controversial changes,
 such as renaming, adding or removing zones, please read
 “Theory and pragmatics of the tz code and data”
-<https://www.iana.org/time-zones/repository/theory.html>.
+<https://data.iana.org/time-zones/theory.html>
 It is also good to browse the mailing list archives
 <https://lists.iana.org/hyperkitty/list/[email protected]/>
 for examples of patches that tend to work well.
@@ -172,9 +172,9 @@ EXPIRES_LINE=	0

 TZDATA_TEXT=	leapseconds tzdata.zi

-# For backward-compatibility links for old zone names, use
+# For backward-compatibility links and zones for old names, use
 #	BACKWARD=	backward
-# To omit these links, use
+# To omit these links and zones, use
 #	BACKWARD=

 BACKWARD=	backward
@@ -574,7 +574,7 @@ SAFE_CHAR=	'[]'$(SAFE_CHARSET)'-]'
 # These non-alphabetic, non-ASCII printable characters are
 # used in commentary or in generated *.txt files
 # and are not likely to cause confusion.
-UNUSUAL_OK_CHARSET= §«°±»½¾×–‘’“”•→−≤★⟨⟩⯪
+UNUSUAL_OK_CHARSET= §«°±»½¾¿×–‘’“”•→−≤★⟨⟩⯪

 # Put this in a bracket expression to match spaces.
 s = [:space:]
@@ -922,7 +922,7 @@ check_mild: check_web check_zishrink \
 UTF8_LOCALE_MISSING = \
  { test ! '$(UTF8_LOCALE)' \
    || ! printf 'A\304\200B\n' \
-         | LC_ALL='$(UTF8_LOCALE)' grep -q '^A.B$$' >/dev/null 2>&1 \
+         | LC_ALL='$(UTF8_LOCALE)' grep -q '^A[[:alpha:]]B$$' >/dev/null 2>&1 \
    || { export LC_ALL='$(UTF8_LOCALE)'; false; }; }

 character-set.ck: $(ENCHILADA)
@@ -1006,11 +1006,11 @@ now.ck: checknow.awk date tzdata.zi zdump zic zone1970.tab zonenow.tab
 		now=$(CHECK_NOW_TIMESTAMP) && \
 		  future=$$(($(CHECK_NOW_FUTURE_SECS) + $$now)) && \
 		  ./zdump -i -t $$now,$$future \
-		     $$(find "$$PWD/$@d"/????*/ -type f) \
+		     $$(find "$$PWD/$@d"/????*/ -type f -o -type l) \
 		     >$@d/zdump-now.tab && \
 		  ./zdump -i -t 0,$$future \
 		     $$(find "$$PWD/$@d" -name Etc -prune \
-			  -o -type f ! -name '*.tab' -print) \
+			  -o \( -type f -o -type l \) ! -name '*.tab' -print) \
 		     >$@d/zdump-1970.tab && \
 		$(AWK) \
 		  -v now=$$now \
@@ -1018,7 +1018,12 @@ now.ck: checknow.awk date tzdata.zi zdump zic zone1970.tab zonenow.tab
 		  -v zdump_table=$@d/zdump-now.tab \
 		  -f checknow.awk zonenow.tab
 		$(AWK) \
-		  'BEGIN {print "-\t-\tUTC"} /^Zone/ {print "-\t-\t" $$2}' \
+		  'BEGIN { \
+		     SysVzone["EST5EDT"] = 1; SysVzone["CST6CDT"] = 1; \
+		     SysVzone["MST7MDT"] = 1; SysVzone["PST8PDT"] = 1; \
+		     print "-\t-\tUTC" \
+		   } \
+		   $$1 == "Zone" && !SysVzone[$$2] {print "-\t-\t" $$2}' \
 		  $(PRIMARY_YDATA) backward factory | \
 		 $(AWK) \
 		   -v zdump_table=$@d/zdump-1970.tab \
@@ -1,5 +1,87 @@
 News for the tz database

+Release 2026d - 2026-09-11 15:21:07 -0700
+
+  Briefly:
+    Canada’s Northwest Territories moved to permanent -06 on 2026-08-21.
+    Obsolescent settings like TZ="EST5EDT" now conform better to POSIX.
+    Fix security, performance and porting bugs in zic and localtime.
+
+  Changes to future timestamps
+
+    Canada’s Northwest Territories will not fall back on 2026-11-01
+    and will stay on -06 year-round, matching Alberta’s recent change.
+    Model this with its traditional abbreviation CST.  Although the
+    change to permanent -06 legally took place on 2026-08-21,
+    temporarily model the change to occur on 2026-11-01 at 02:00
+    for the same reason as other recent temporary hacks.  (Caution:
+    see “NOTE FOR 2026b TEMPORARY HACK FOR CLDR AND CANADA” below.)
+    This affects only America/Inuvik as the rest of the territory is
+    covered by America/Edmonton, for which the equivalent change was
+    released in 2026c.
+
+  Changes to past timestamps
+
+    Colombia’s 1992-05-02 spring forward was at 00:00, not 24:00.
+
+    Iran’s 1979-05-26 spring forward was at 00:00, not 24:00.
+    (Thanks to N.F. Hase.)
+
+    The backward-compatibility names EST5EDT, CST6CDT, MST7MDT, and
+    PST8PDT now conform better to POSIX.  For example, EST5EDT now
+    always uses the abbreviation "EST" for standard time (now always 5
+    hours behind UT) and "EDT" for daylight saving time, whereas it
+    formerly had different UT offsets before standard time was
+    introduced and sometimes used abbreviations like "LMT", "EWT" and
+    "EPT", all contrary to POSIX.  Also, though not required by POSIX
+    these names now use US federal rules rather than rules of places
+    like New York, reverting to 2024a behavior.  This change affects
+    only timestamps before 1966-10-30 at 01:00 standard time.
+
+  Other data changes
+
+    The temporary hacks used for North American timekeeping changes
+    now work around a libstdc++ std::chrono bug in GCC 14.1-14.4,
+    15.1-15.2, and 16.1; see GCC bug 124851.  This data change does
+    not affect TZif files or timestamps.  The change does not work
+    around the related but less serious GCC bugs 116110 and 124513.
+    These GCC bugs are all fixed in GCC 16.2.
+
+  Changes to code
+
+    zic now rejects Link targets that would have invalid names, and
+    more efficiently processes Expires, Leap and Rule lines with years
+    far in the past or future.  (Thanks to Darren Carreras.)
+
+    zic now ports to systems that report lack of link support via
+    EINVAL, ENOSYS or EPERM errno values. (Thanks to Tom Lane.)
+
+    When tzset and related functions encounter a TZif file that is too
+    large for them, they now consistently fail instead of sometimes
+    silently ignoring excess parts of the file.
+
+    localtime-related functions no longer mishandle extreme timestamps
+    when given TZif files holding some unlikely timezone histories.
+    (Problem reported by David Sarkisyan.)
+
+    localtime-related functions no longer check the values of TZif
+    files’ standard/wall and UT/local indicators, which these
+    functions have not used since 2026a’s removal of the old
+    posixrules feature.
+
+    tzcode has been ported to Haiku.
+
+    localtime.c now works again by default on AIX and DragonFly BSD.
+
+    zic now rejects ‘:’ and ‘\’ in Zone and Link names when running on
+    Microsoft Windows.  (Problem reported by David Diaz.)
+
+  Changes to documentation
+
+    URLs for release tarballs in tz-link.html have been updated to
+    reflect their new canonical URLs on data.iana.org.
+
+
 Release 2026c - 2026-07-08 10:23:58 -0700

  Briefly:
@@ -15,7 +97,13 @@ Release 2026c - 2026-07-08 10:23:58 -0700
    CST.  Although the change to permanent -06 legally took place on
    2026-06-18, temporarily model the change to occur on 2026-11-01 at
    02:00 instead, for the same reason we introduced a similarly
-    temporary hack for British Columbia in 2026b.
+    temporary hack for British Columbia in 2026b.  (Caution: see
+    “NOTE FOR 2026b TEMPORARY HACK FOR CLDR AND CANADA” below.)
+
+      As the change affects both America/Edmonton and its backward
+      compatibility link, the obsolescent setting TZ="Canada/Mountain"
+      will now use the abbreviation CST for affected timestamps,
+      akin to TZ="Canada/Pacific" behavior introduced in 2026b.

      Although another TZDB release will likely be needed soon because
      Northwest Territories will likely follow Alberta, the legal
@@ -67,6 +155,7 @@ Release 2026b - 2026-04-22 23:06:43 -0700

  Briefly:
    British Columbia moved to permanent -07 on 2026-03-09.
+    zic no longer mishandles a last transition to a new time type.
    Some more overflow bugs have been fixed in zic.

  Changes to future timestamps
@@ -79,9 +168,33 @@ Release 2026b - 2026-04-22 23:06:43 -0700
    limitation in CLDR 48.1 (2026-01-08).  This temporary hack is
    planned to be removed after CLDR is fixed.

+      To match longstanding practice for -07 standard time in North
+      America, such as for America/Dawson, America/Dawson_Creek,
+      America/Fort_Nelson and America/Whitehorse, affected BC
+      timestamps use the abbreviation MST.  As the change affects both
+      America/Vancouver and its backward compatibility link, the
+      obsolescent setting TZ="Canada/Pacific" will now use the
+      abbreviation MST.  Future TZDB releases may change the
+      abbreviation if something else becomes popular across areas
+      observing -07, and may change it to "-07" if no alphabetic
+      consensus emerges.
+
  Changes to code

    zic no longer mishandles a last transition to a new time type.
+    NOTE FOR 2026b TEMPORARY HACK FOR CLDR AND CANADA:
+    This zic fix is needed for the temporary hack (mentioned above)
+    that works around the Canadian timekeeping bug in Unicode CLDR.
+    Without the fix, the temporary hack causes zic versions 2023d
+    through 2026a, in their default mode that generates slim output,
+    to generate a TZif file that violates Internet RFC 9636 §3.3.
+    The buggy file in turn causes some TZif readers, including tzcode
+    itself, to ignore America/Vancouver’s 2026-11-01 02:00 transition
+    from PDT (tm_isdst=1) to MST (tm_isdst=0).  Although the buggy
+    file does not cause any known TZif reader to mishandle UT offsets,
+    caution is advised when using zic 2023d through 2026a to compile
+    data from more-recent tz releases.  To work around this problem
+    when using these older zic versions, use ‘zic -b fat’.

    zic no longer overflows a buffer when generating a TZ string like
    "PST-167:59:58PDT-167:59:59,M11.5.6/-167:59:59,M12.5.6/-167:59:59",
@@ -10,7 +10,7 @@ locations around the globe.  It is updated periodically to reflect
 changes made by political bodies to time zone boundaries, UTC offsets,
 and daylight-saving rules.

-See <https://www.iana.org/time-zones/repository/tz-link.html> or the
+See <https://data.iana.org/time-zones/tz-link.html> or the
 file tz-link.html for how to acquire the code and data.

 Once acquired, read the leading comments in the file ‘Makefile’
@@ -64,7 +64,7 @@ struct stat { char st_ctime, st_dev, st_ino; };
 # endif
 # if THREAD_PREFER_SINGLE
 #  ifndef HAVE___ISTHREADED
-#   if defined __FreeBSD__ || defined __OpenBSD__
+#   if defined __FreeBSD__ || defined __OpenBSD__ || defined __DragonFly__
 #    define HAVE___ISTHREADED 1
 #   else
 #    define HAVE___ISTHREADED 0
@@ -348,6 +348,10 @@ static int fstatat(int dd, char const *path, struct stat *st, int flags)
 #  include <sys/auxv.h>
 # endif

+/* Avoid clash if headers declare but libraries do not define issetugid.  */
+# undef issetugid
+# define issetugid localtime_issetugid
+
 /* Return 1 if the process is privileged, 0 otherwise.  */
 static int
 issetugid(void)
@@ -475,8 +479,6 @@ struct ttinfo {				/* time type information */
 					   -2**31 + 1 .. 2**31 - 1  */
 	desigidx_type	tt_desigidx;	/* abbreviation list index */
 	bool		tt_isdst;	/* used to set tm_isdst */
-	bool		tt_ttisstd;	/* transition is std time */
-	bool		tt_ttisut;	/* transition is UT */
 };

 struct lsinfo {				/* leap second information */
@@ -505,7 +507,6 @@ struct state {
 	int		timecnt;
 	int		typecnt;
 	int		charcnt;
-	bool		goback;
 	bool		goahead;
 	time_t		ats[TZ_MAX_TIMES];
 	unsigned char	types[TZ_MAX_TIMES];
@@ -569,12 +570,11 @@ struct rule {
 };

 static struct tm *gmtsub(struct state const *, time_t const *, int_fast32_t,
-			 struct tm *);
-static bool increment_overflow(int *, int);
+			 struct tm *, time_t *);
 static bool increment_overflow_time(time_t *, int_fast32_2s);
 static int_fast32_2s leapcorr(struct state const *, time_t);
 static struct tm *timesub(time_t const *, int_fast32_t, struct state const *,
-			  struct tm *);
+			  struct tm *, time_t *);
 static bool tzparse(char const *, struct state *, struct state const *);

 #ifndef ALL_STATE
@@ -641,8 +641,6 @@ init_ttinfo(struct ttinfo *s, int_fast32_t utoff, bool isdst,
  s->tt_utoff = utoff;
  s->tt_isdst = isdst;
  s->tt_desigidx = desigidx;
-  s->tt_ttisstd = false;
-  s->tt_ttisut = false;
 }

 /* Return true if SP's time type I does not specify local time.  */
@@ -838,10 +836,11 @@ tzfile_changed(int fd, struct stat *st)
       resolution if available, as this can help distinguish files on
       non-POSIX platforms where st_dev and st_ino are unreliable.  */
    struct timespec ctim;
-#if HAVE_STRUCT_STAT_ST_CTIM
-    ctim = st->st_ctim;
-#else
+    /* Copy via members, as AIX 7.3 defaults to an incompatible st_ctim.  */
    ctim.tv_sec = st->st_ctime;
+#if HAVE_STRUCT_STAT_ST_CTIM
+    ctim.tv_nsec = st->st_ctim.tv_nsec;
+#else
    ctim.tv_nsec = 0;
 #endif

@@ -896,9 +895,19 @@ union local_storage {
 };

 /* These tzload flags can be ORed together, and fit into 'char'.  */
-enum { TZLOAD_FROMENV = 1 }; /* The TZ string came from the environment.  */
-enum { TZLOAD_TZSTRING = 2 }; /* Read any newline-surrounded TZ string.  */
-enum { TZLOAD_TZDIR_SUB = 4 }; /* TZ should be a file under TZDIR.  */
+
+/* TZLOAD_FROMENV means the TZ string is a process-wide setting either
+   taken from the TZ environment variable or inferred from TZ being unset.
+   When 0 <= tz_change_interval, TZLOAD_FROMENV lets us skip reanalysis
+   of a TZif file that did not change during the interval.  */
+enum { TZLOAD_FROMENV = 1 };
+
+/* Read any newline-surrounded TZ string.  */
+enum { TZLOAD_TZSTRING = 2 };
+
+/* TZ should be a file under TZDIR.  */
+enum { TZLOAD_TZDIR_SUB = 4 };
+

 /* Load tz data from the file named NAME into *SP.  Respect TZLOADFLAGS.
   Use **LSPP for temporary storage.  Return 0 on
@@ -923,7 +932,7 @@ tzloadbody(char const *name, struct state *sp, char tzloadflags,
 	struct stat st;
 	st.st_ctime = 0;

-	sp->goback = sp->goahead = false;
+	sp->goahead = false;

 	if (! name) {
 		name = TZDEFAULT;
@@ -1198,30 +1207,9 @@ tzloadbody(char const *name, struct state *sp, char tzloadflags,
 		}
 		set_leapcount(sp, leapcnt);

-		for (i = 0; i < sp->typecnt; ++i) {
-			register struct ttinfo *	ttisp;
-
-			ttisp = &sp->ttis[i];
-			if (ttisstdcnt == 0)
-				ttisp->tt_ttisstd = false;
-			else {
-				if (*p != true && *p != false)
-				  return EFTYPE;
-				ttisp->tt_ttisstd = *p++;
-			}
-		}
-		for (i = 0; i < sp->typecnt; ++i) {
-			register struct ttinfo *	ttisp;
-
-			ttisp = &sp->ttis[i];
-			if (ttisutcnt == 0)
-				ttisp->tt_ttisut = false;
-			else {
-				if (*p != true && *p != false)
-						return EFTYPE;
-				ttisp->tt_ttisut = *p++;
-			}
-		}
+		/* Do not bother to validate standard/wall and UT/local
+		   indicators, as they are no longer used here.  */
+		p += ttisstdcnt + ttisutcnt;
 	    }

 	    nread -= p - up->buf;
@@ -1232,13 +1220,13 @@ tzloadbody(char const *name, struct state *sp, char tzloadflags,
 	      break;
 	}
 	if ((tzloadflags & TZLOAD_TZSTRING) && nread > 2 &&
-		up->buf[0] == '\n' && up->buf[nread - 1] == '\n' &&
-		sp->typecnt + 2 <= TZ_MAX_TYPES) {
+		up->buf[0] == '\n' && up->buf[nread - 1] == '\n') {
 			struct state	*ts = &lsp->u.st;

 			up->buf[nread - 1] = '\0';
-			if (tzparse(&up->buf[1], ts, sp)) {
-
+			if (!tzparse(&up->buf[1], ts, sp))
+			  return EFTYPE;
+			else {
 			  /* Attempt to reuse existing abbreviations.
 			     Without this, America/Anchorage would
 			     consume 50 bytes for abbreviations, as
@@ -1246,7 +1234,6 @@ tzloadbody(char const *name, struct state *sp, char tzloadflags,
 			     AHDT YST AKDT AKST) and ts->charcnt equals 10
 			     (for AKST AKDT).  Reusing means sp->charcnt can
 			     stay 40 in this example.  */
-			  int gotabbr = 0;
 			  int charcnt = sp->charcnt;
 			  for (i = 0; i < ts->typecnt; i++) {
 			    char *tsabbr = ts->chars + ts->ttis[i].tt_desigidx;
@@ -1254,22 +1241,25 @@ tzloadbody(char const *name, struct state *sp, char tzloadflags,
 			    for (j = 0; j < charcnt; j++)
 			      if (strcmp(sp->chars + j, tsabbr) == 0) {
 				ts->ttis[i].tt_desigidx = j;
-				gotabbr++;
 				break;
 			      }
 			    if (! (j < charcnt)) {
 			      int tsabbrlen = strnlen(tsabbr, TZ_MAX_CHARS - j);
-			      if (j + tsabbrlen < TZ_MAX_CHARS) {
+			      if (TZ_MAX_CHARS <= j + tsabbrlen)
+				return EOVERFLOW;
+			      else {
 				char *cp = sp->chars + j;
 				cp = mempcpy(cp, tsabbr, tsabbrlen);
 				*cp = '\0';
 				charcnt = j + tsabbrlen + 1;
 				ts->ttis[i].tt_desigidx = j;
-				gotabbr++;
 			      }
 			    }
 			  }
-			  if (gotabbr == ts->typecnt) {
+
+			  if (TZ_MAX_TYPES - sp->typecnt < ts->typecnt)
+			    return EOVERFLOW;
+			  else {
 			    sp->charcnt = charcnt;

 			    /* Ignore any trailing, no-op transitions generated
@@ -1288,10 +1278,8 @@ tzloadbody(char const *name, struct state *sp, char tzloadflags,
 				  || (0 < sp->timecnt
 				      && t <= sp->ats[sp->timecnt - 1]))
 				continue;
-			      if (TZ_MAX_TIMES <= sp->timecnt) {
-				sp->goahead = false;
-				break;
-			      }
+			      if (TZ_MAX_TIMES <= sp->timecnt)
+				return EOVERFLOW;
 			      sp->ats[sp->timecnt] = t;
 			      sp->types[sp->timecnt] = (sp->typecnt
 							+ ts->types[i]);
@@ -1334,10 +1322,6 @@ static const int	mon_lengths[2][MONSPERYEAR] = {
 	{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
 };

-static const int	year_lengths[2] = {
-	DAYSPERNYEAR, DAYSPERLYEAR
-};
-
 /* Is C an ASCII digit?  */
 static bool
 is_digit(char c)
@@ -1537,40 +1521,26 @@ getrule(const char *strp, register struct rule *const rulep)
 */

 static int_fast32_t
-transtime(const int year, register const struct rule *const rulep,
+transtime(time_t year, register const struct rule *const rulep,
 	  const int_fast32_t offset)
 {
+	int d;  /* Day of year (zero-origin).  */
 	register bool	leapyear;
-	register int_fast32_t value;
-	register int	i;
-	int		d, m1, yy0, yy1, yy2, dow;

 	leapyear = isleap(year);
-	switch (rulep->r_type) {

-	case JULIAN_DAY:
+	if (rulep->r_type <= DAY_OF_YEAR) {
 		/*
 		** Jn - Julian day, 1 == January 1, 60 == March 1 even in leap
 		** years.
 		** In non-leap years, or if the day number is 59 or less, just
-		** add SECSPERDAY times the day number-1 to the time of
-		** January 1, midnight, to get the day.
-		*/
-		value = (rulep->r_day - 1) * SECSPERDAY;
-		if (leapyear && rulep->r_day >= 60)
-			value += SECSPERDAY;
-		break;
-
-	case DAY_OF_YEAR:
-		/*
+		** use the day number - 1.
+		**
 		** n - day of year.
-		** Just add SECSPERDAY times the day number to the time of
-		** January 1, midnight, to get the day.
 		*/
-		value = rulep->r_day * SECSPERDAY;
-		break;
-
-	case MONTH_NTH_DAY_OF_WEEK:
+		d = rulep->r_day - ((rulep->r_type < DAY_OF_YEAR)
+				    & (!leapyear | (rulep->r_day <= 59)));
+	} else {
 		/*
 		** Mm.n.d - nth "dth day" of month m.
 		*/
@@ -1579,14 +1549,16 @@ transtime(const int year, register const struct rule *const rulep,
 		** Use Zeller's Congruence to get day-of-week of first day of
 		** month.
 		*/
-		m1 = (rulep->r_mon + 9) % 12 + 1;
-		yy0 = (rulep->r_mon <= 2) ? (year - 1) : year;
-		yy1 = yy0 / 100;
-		yy2 = yy0 % 100;
-		dow = ((26 * m1 - 2) / 10 +
-			1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
-		if (dow < 0)
-			dow += DAYSPERWEEK;
+		int i;
+		bool janfeb = rulep->r_mon <= 2;
+		int month = (rulep->r_mon
+			     + (janfeb ? MONSPERYEAR : 0)); /* 3..14  */
+		int adjustment = (TYPE_SIGNED(time_t) ? 0 : 400) - janfeb;
+		int ay_rem = (year + adjustment) % YEARSPERREPEAT;
+		int y = ay_rem + (ay_rem < 0 ? YEARSPERREPEAT : 0);
+		int dow = (((13 * (month + 1)) / 5
+			    + y + y / 4 - y / 100 + y / 400)
+			   % DAYSPERWEEK);

 		/*
 		** "dow" is the day-of-week of the first day of the month. Get
@@ -1594,33 +1566,24 @@ transtime(const int year, register const struct rule *const rulep,
 		** month.
 		*/
 		d = rulep->r_day - dow;
-		if (d < 0)
-			d += DAYSPERWEEK;
-		for (i = 1; i < rulep->r_week; ++i) {
-			if (d + DAYSPERWEEK >=
-				mon_lengths[leapyear][rulep->r_mon - 1])
-					break;
-			d += DAYSPERWEEK;
-		}
+		d += (rulep->r_week - (0 <= d)) * DAYSPERWEEK;
+		if (mon_lengths[leapyear][rulep->r_mon - 1] <= d)
+		  d -= DAYSPERWEEK;

 		/*
 		** "d" is the day-of-month (zero-origin) of the day we want.
 		*/
-		value = d * SECSPERDAY;
 		for (i = 0; i < rulep->r_mon - 1; ++i)
-			value += mon_lengths[leapyear][i] * SECSPERDAY;
-		break;
-
-	default: unreachable();
+		  d += mon_lengths[leapyear][i];
 	}

 	/*
-	** "value" is the year-relative time of 00:00:00 UT on the day in
+	** d is the origin-0 year-relative day in
 	** question. To get the year-relative time of the specified local
 	** time on that day, add the transition time and the current offset
-	** from UT.
+	** from UT to d * SECSPERDAY.
 	*/
-	return value + rulep->r_time + offset;
+	return d * SECSPERDAY + rulep->r_time + offset;
 }

 /*
@@ -1670,11 +1633,11 @@ tzparse(const char *name, struct state *sp, struct state const *basep)
 	  }
 	} else
 	  set_leapcount(sp, 0);	/* So, we're off a little.  */
-	sp->goback = sp->goahead = false;
+	sp->goahead = false;
 	if (*name != '\0') {
 		struct rule start, end;
-		int year, yearbeg, yearlim, timecnt;
-		time_t janfirst;
+		int timecnt;
+		time_t janfirst, repeatbeg, year, yearbeg, yearlim;
 		int_fast32_t janoffset = 0;

 		if (*name == '<') {
@@ -1712,18 +1675,20 @@ tzparse(const char *name, struct state *sp, struct state const *basep)
 		if (!name || *name)
 		  return false;
 		sp->typecnt = 2;	/* standard time and DST */
-		/*
-		** Two transitions per year, from EPOCH_YEAR forward.
-		*/
+
+		/* Two transitions per year, from atlo forward, and going on
+		   for years_of_observations past max(atlo, leaplo).  */
 		init_ttinfo(&sp->ttis[0], -stdoffset, false, 0);
 		init_ttinfo(&sp->ttis[1], -dstoffset, true, stdlen + 1);
 		timecnt = 0;
-		janfirst = 0;
-		yearbeg = EPOCH_YEAR;
+		repeatbeg = (atlo / SECSPERREPEAT
+			     + (atlo < 0 && 0 < atlo % SECSPERREPEAT));
+		yearbeg = repeatbeg * YEARSPERREPEAT + EPOCH_YEAR;
+		janfirst = repeatbeg * SECSPERREPEAT;

 		do {
 		  int_fast32_t yearsecs
-		    = year_lengths[isleap(yearbeg - 1)] * SECSPERDAY;
+		    = year_days(yearbeg - 1) * SECSPERDAY;
 		  time_t janfirst1 = janfirst;
 		  yearbeg--;
 		  if (increment_overflow_time(&janfirst1, -yearsecs)) {
@@ -1731,30 +1696,25 @@ tzparse(const char *name, struct state *sp, struct state const *basep)
 		    break;
 		  }
 		  janfirst = janfirst1;
-		} while (atlo < janfirst
-			 && EPOCH_YEAR - YEARSPERREPEAT / 2 < yearbeg);
+		} while (atlo < janfirst);

 		while (true) {
 		  int_fast32_t yearsecs
-		    = year_lengths[isleap(yearbeg)] * SECSPERDAY;
-		  int yearbeg1 = yearbeg;
+		    = year_days(yearbeg) * SECSPERDAY;
 		  time_t janfirst1 = janfirst;
 		  if (increment_overflow_time(&janfirst1, yearsecs)
-		      || increment_overflow(&yearbeg1, 1)
 		      || atlo <= janfirst1)
 		    break;
-		  yearbeg = yearbeg1;
+		  yearbeg++;
 		  janfirst = janfirst1;
 		}

-		yearlim = yearbeg;
-		if (increment_overflow(&yearlim, years_of_observations))
-		  yearlim = INT_MAX;
+		yearlim = yearbeg + years_of_observations;
 		for (year = yearbeg; year < yearlim; year++) {
 		  int_fast32_t
 		    starttime = transtime(year, &start, stdoffset),
 		    endtime = transtime(year, &end, dstoffset),
-		    yearsecs = year_lengths[isleap(year)] * SECSPERDAY;
+		    yearsecs = year_days(year) * SECSPERDAY;
 		  bool reversed = endtime < starttime;
 		  if (reversed) {
 		    int_fast32_t swap = starttime;
@@ -1764,24 +1724,25 @@ tzparse(const char *name, struct state *sp, struct state const *basep)
 		  if (reversed
 		      || (starttime < endtime
 			  && endtime - starttime < yearsecs)) {
-		    if (TZ_MAX_TIMES - 2 < timecnt)
-		      break;
-		    sp->ats[timecnt] = janfirst;
-		    if (! increment_overflow_time(&sp->ats[timecnt],
-						  janoffset + starttime)
-			&& atlo <= sp->ats[timecnt])
+		    time_t at_added = TIME_T_MAX;
+		    time_t at = janfirst;
+		    if (! increment_overflow_time(&at, janoffset + starttime)
+			&& atlo <= at) {
+		      if (TZ_MAX_TIMES <= timecnt)
+			return false;
+		      sp->ats[timecnt] = at_added = at;
 		      sp->types[timecnt++] = !reversed;
-		    sp->ats[timecnt] = janfirst;
-		    if (! increment_overflow_time(&sp->ats[timecnt],
-						  janoffset + endtime)
-			&& atlo <= sp->ats[timecnt]) {
+		    }
+		    at = janfirst;
+		    if (! increment_overflow_time(&at, janoffset + endtime)
+			&& atlo <= at) {
+		      if (TZ_MAX_TIMES <= timecnt)
+			return false;
+		      sp->ats[timecnt] = at_added = at;
 		      sp->types[timecnt++] = reversed;
 		    }
-		  }
-		  if (endtime < leaplo) {
-		    yearlim = year;
-		    if (increment_overflow(&yearlim, years_of_observations))
-		      yearlim = INT_MAX;
+		    if (at_added < leaplo)
+		      yearlim = year + years_of_observations;
 		  }
 		  if (increment_overflow_time(&janfirst, janoffset + yearsecs))
 		    break;
@@ -1792,7 +1753,7 @@ tzparse(const char *name, struct state *sp, struct state const *basep)
 		  sp->ttis[0] = sp->ttis[1];
 		  sp->typecnt = 1;	/* Perpetual DST.  */
 		} else if (years_of_observations <= year - yearbeg)
-		  sp->goback = sp->goahead = true;
+		  sp->goahead = true;
 	} else {
 		dstlen = 0;
 		sp->typecnt = 1;		/* only standard time */
@@ -1849,7 +1810,7 @@ zoneinit(struct state *sp, char const *name, char tzloadflags)
    sp->timecnt = 0;
    sp->typecnt = 0;
    sp->charcnt = 0;
-    sp->goback = sp->goahead = false;
+    sp->goahead = false;
    init_ttinfo(&sp->ttis[0], 0, false, 0);
    strcpy(sp->chars, utc);
    return 0;
@@ -2069,12 +2030,15 @@ tzfree(timezone_t sp)
 ** since in that case tzset should have already done this step correctly.
 ** SETNAME's type is int_fast32_t for compatibility with gmtsub,
 ** but it is actually a boolean and its value should be 0 or 1.
+**
+** If LTM_YEAR, store the resulting year-1900 into *LTM_YEAR rather
+** than into the default TMP->tm_year; this prevents year overflow.
 */

 /*ARGSUSED*/
 static struct tm *
 localsub(struct state const *sp, time_t const *timep, int_fast32_t setname,
-	 struct tm *const tmp)
+	 struct tm *tmp, time_t *ltm_year)
 {
 	register const struct ttinfo *	ttisp;
 	register int			i;
@@ -2083,52 +2047,39 @@ localsub(struct state const *sp, time_t const *timep, int_fast32_t setname,

 	if (sp == NULL) {
 	  /* Don't bother to set tzname etc.; tzset has already done it.  */
-	  return gmtsub(gmtptr, timep, 0, tmp);
+	  return gmtsub(gmtptr, timep, 0, tmp, ltm_year);
 	}
-	if ((sp->goback && t < sp->ats[0]) ||
-		(sp->goahead && t > sp->ats[sp->timecnt - 1])) {
-			time_t newt;
-			register time_t		seconds;
-			register time_t		years;
+	if (sp->goahead && sp->ats[sp->timecnt - 1] < t) {
+			/* Avoid integer overflow when time_t is signed, by
+			   using secs_div_2 twice; the full value would
+			   always be even, so halving does not round.  */
+			time_t
+			  tlo = sp->ats[sp->timecnt - 1],
+			  diffyears = ((t / 2 - tlo / 2
+					+ ((t % 2 - tlo % 2 + 2) / 2 - 1))
+				       / (SECSPERREPEAT / 2)
+				       * YEARSPERREPEAT),
+			  years = diffyears + YEARSPERREPEAT,
+			  secs_div_2 = (diffyears * (AVGSECSPERYEAR / 2)
+					+ SECSPERREPEAT / 2),
+			  newt = t - secs_div_2 - secs_div_2,
+			  ryear;

-			if (t < sp->ats[0])
-				seconds = sp->ats[0] - t;
-			else	seconds = t - sp->ats[sp->timecnt - 1];
-			--seconds;
-
-			/* Beware integer overflow, as SECONDS might
-			   be close to the maximum time_t.  */
-			years = seconds / SECSPERREPEAT * YEARSPERREPEAT;
-			seconds = years * AVGSECSPERYEAR;
-			years += YEARSPERREPEAT;
-			if (t < sp->ats[0])
-			  newt = t + seconds + SECSPERREPEAT;
-			else
-			  newt = t - seconds - SECSPERREPEAT;
-
-			if (newt < sp->ats[0] ||
-				newt > sp->ats[sp->timecnt - 1])
-					return NULL;	/* "cannot happen" */
-			result = localsub(sp, &newt, setname, tmp);
+			result = localsub(sp, &newt, setname, tmp, &ryear);
 			if (result) {
-# if defined ckd_add && defined ckd_sub
-				if (t < sp->ats[0]
-				    ? ckd_sub(&result->tm_year,
-					      result->tm_year, years)
-				    : ckd_add(&result->tm_year,
-					      result->tm_year, years))
+			  if (ltm_year)
+			    *ltm_year = ryear + years;
+			  else {
+# ifdef ckd_add
+				if (ckd_add(&result->tm_year, ryear, years))
 				  return NULL;
 # else
-				register int_fast64_t newy;
-
-				newy = result->tm_year;
-				if (t < sp->ats[0])
-					newy -= years;
-				else	newy += years;
+				time_t newy = ryear + years;
 				if (! (INT_MIN <= newy && newy <= INT_MAX))
 					return NULL;
 				result->tm_year = newy;
 # endif
+			  }
 			}
 			return result;
 	}
@@ -2152,9 +2103,9 @@ localsub(struct state const *sp, time_t const *timep, int_fast32_t setname,
 	** To get (wrong) behavior that's compatible with System V Release 2.0
 	** you'd replace the statement below with
 	**	t += ttisp->tt_utoff;
-	**	timesub(&t, 0, sp, tmp);
+	**	timesub(&t, 0, sp, tmp, ltm_year);
 	*/
-	result = timesub(&t, ttisp->tt_utoff, sp, tmp);
+	result = timesub(&t, ttisp->tt_utoff, sp, tmp, ltm_year);
 	if (result) {
 	  result->tm_isdst = ttisp->tt_isdst;
 # ifdef TM_ZONE
@@ -2204,7 +2155,7 @@ struct tm *
 localtime_rz(struct state *restrict sp, time_t const *restrict timep,
 	     struct tm *restrict tmp)
 {
-  return localsub(sp, timep, 0, tmp);
+  return localsub(sp, timep, 0, tmp, NULL);
 }
 # endif

@@ -2219,7 +2170,7 @@ localtime_tzset(time_t const *timep, struct tm *tmp, bool setname)
  }
  if (0 <= tz_change_interval || setname || !lcl_is_set)
    tzset_unlocked(!err, false, now);
-  tmp = localsub(lclptr, timep, setname, tmp);
+  tmp = localsub(lclptr, timep, setname, tmp, NULL);
  unlock(!err);
  return tmp;
 }
@@ -2246,11 +2197,11 @@ localtime_r(const time_t *restrict timep, struct tm *restrict tmp)

 static struct tm *
 gmtsub(ATTRIBUTE_MAYBE_UNUSED struct state const *sp, time_t const *timep,
-       int_fast32_t offset, struct tm *tmp)
+       int_fast32_t offset, struct tm *tmp, time_t *ltm_year)
 {
 	register struct tm *	result;

-	result = timesub(timep, offset, gmtptr, tmp);
+	result = timesub(timep, offset, gmtptr, tmp, ltm_year);
 #ifdef TM_ZONE
 	/*
 	** Could get fancy here and deliver something such as
@@ -2273,7 +2224,7 @@ struct tm *
 gmtime_r(time_t const *restrict timep, struct tm *restrict tmp)
 {
  gmtcheck();
-  return gmtsub(gmtptr, timep, 0, tmp);
+  return gmtsub(gmtptr, timep, 0, tmp, NULL);
 }

 struct tm *
@@ -2294,7 +2245,7 @@ struct tm *
 offtime_r(time_t const *restrict timep, long offset, struct tm *restrict tmp)
 {
  gmtcheck();
-  return gmtsub(gmtptr, timep, offset, tmp);
+  return gmtsub(gmtptr, timep, offset, tmp, NULL);
 }

 struct tm *
@@ -2330,7 +2281,7 @@ leaps_thru_end_of(time_t y)

 static struct tm *
 timesub(const time_t *timep, int_fast32_t offset,
-	const struct state *sp, struct tm *tmp)
+	const struct state *sp, struct tm *tmp, time_t *ltm_year)
 {
 	register time_t			tdays;
 	register const int *		ip;
@@ -2380,7 +2331,7 @@ timesub(const time_t *timep, int_fast32_t offset,
 	idays += dayoff % DAYSPERREPEAT + 2 * DAYSPERREPEAT;
 	idays %= DAYSPERREPEAT;
 	/* Increase Y and decrease IDAYS until IDAYS is in range for Y.  */
-	while (year_lengths[isleap(y)] <= idays) {
+	while (year_days(y) <= idays) {
 		int tdelta = idays / DAYSPERLYEAR;
 		int_fast32_t ydelta = tdelta + !tdelta;
 		time_t newy = y + ydelta;
@@ -2392,29 +2343,34 @@ timesub(const time_t *timep, int_fast32_t offset,
 		y = newy;
 	}

+	if (ltm_year) {
+	  *ltm_year = y - TM_YEAR_BASE;
+	} else {
 #ifdef ckd_add
-	if (ckd_add(&tmp->tm_year, y, -TM_YEAR_BASE)) {
-	  errno = EOVERFLOW;
-	  return NULL;
-	}
+	  if (ckd_add(&tmp->tm_year, y, -TM_YEAR_BASE)) {
+	    errno = EOVERFLOW;
+	    return NULL;
+	  }
 #else
-	if (!TYPE_SIGNED(time_t) && y < TM_YEAR_BASE) {
-	  int signed_y = y;
-	  tmp->tm_year = signed_y - TM_YEAR_BASE;
-	} else if ((!TYPE_SIGNED(time_t) || INT_MIN + TM_YEAR_BASE <= y)
-		   && y - TM_YEAR_BASE <= INT_MAX)
-	  tmp->tm_year = y - TM_YEAR_BASE;
-	else {
-	  errno = EOVERFLOW;
-	  return NULL;
-	}
+	  if (!TYPE_SIGNED(time_t) && y < TM_YEAR_BASE) {
+	    int signed_y = y;
+	    tmp->tm_year = signed_y - TM_YEAR_BASE;
+	  } else if ((!TYPE_SIGNED(time_t) || INT_MIN + TM_YEAR_BASE <= y)
+		     && y - TM_YEAR_BASE <= INT_MAX)
+	    tmp->tm_year = y - TM_YEAR_BASE;
+	  else {
+	    errno = EOVERFLOW;
+	    return NULL;
+	  }
 #endif
+	}
 	tmp->tm_yday = idays;
 	/*
 	** The "extra" mods below avoid overflow problems.
 	*/
 	tmp->tm_wday = (TM_WDAY_BASE
-			+ ((tmp->tm_year % DAYSPERWEEK)
+			+ ((y % DAYSPERWEEK - TM_YEAR_BASE % DAYSPERWEEK)
+			   % DAYSPERWEEK
 			   * (DAYSPERNYEAR % DAYSPERWEEK))
 			+ leaps_thru_end_of(y - 1)
 			- leaps_thru_end_of(TM_YEAR_BASE - 1)
@@ -2459,27 +2415,6 @@ timesub(const time_t *timep, int_fast32_t offset,
 ** Normalize logic courtesy Paul Eggert.
 */

-static bool
-increment_overflow(int *ip, int j)
-{
-#ifdef ckd_add
-	return ckd_add(ip, *ip, j);
-#else
-	register int const	i = *ip;
-
-	/*
-	** If i >= 0 there can only be overflow if i + j > INT_MAX
-	** or if j > INT_MAX - i; given i >= 0, INT_MAX - i cannot overflow.
-	** If i < 0 there can only be overflow if i + j < INT_MIN
-	** or if j < INT_MIN - i; given i < 0, INT_MIN - i cannot overflow.
-	*/
-	if ((i >= 0) ? (j > INT_MAX - i) : (j < INT_MIN - i))
-		return true;
-	*ip += j;
-	return false;
-#endif
-}
-
 static bool
 increment_overflow_64(int *ip, int_fast64_t j)
 {
@@ -2588,7 +2523,7 @@ mktmcpy(struct tm *dest, struct tm const *src)
 static time_t
 time2sub(struct tm *const tmp,
 	 struct tm *funcp(struct state const *, time_t const *,
-			  int_fast32_t, struct tm *),
+			  int_fast32_t, struct tm *, time_t *),
 	 struct state const *sp,
 	 const int_fast32_t offset,
 	 bool *okayp,
@@ -2648,12 +2583,12 @@ time2sub(struct tm *const tmp,

 	while (mday <= 0) {
 	  iinntt li = y - (yourtm.tm_mon <= 1);
-	  mday += year_lengths[isleap(li)];
+	  mday += year_days(li);
 	  y--;
 	}
 	while (DAYSPERLYEAR < mday) {
 	  iinntt li = y + (1 < yourtm.tm_mon);
-	  mday -= year_lengths[isleap(li)];
+	  mday -= year_days(li);
 	  y++;
 	}
 	yourtm.tm_mday = mday;
@@ -2705,7 +2640,7 @@ time2sub(struct tm *const tmp,
 			t = lo;
 		else if (t > hi)
 			t = hi;
-		if (! funcp(sp, &t, offset, &mytm)) {
+		if (! funcp(sp, &t, offset, &mytm, NULL)) {
 			/*
 			** Assume that t is too extreme to be represented in
 			** a struct tm; arrange things so that it is less
@@ -2761,7 +2696,7 @@ time2sub(struct tm *const tmp,
 # endif
 		  if (!v && !increment_overflow_time_64(&altt, offdiff)) {
 		    struct tm alttm;
-		    if (funcp(sp, &altt, offset, &alttm)
+		    if (funcp(sp, &altt, offset, &alttm, NULL)
 			&& alttm.tm_isdst == mytm.tm_isdst
 			&& alttm.TM_GMTOFF == yourtm.TM_GMTOFF
 			&& tmcomp(&alttm, &yourtm) == 0) {
@@ -2795,7 +2730,7 @@ time2sub(struct tm *const tmp,
 				     utoff_diff(sp->ttis[j].tt_utoff,
 						sp->ttis[i].tt_utoff)))
 				  continue;
-				if (! funcp(sp, &newt, offset, &mytm))
+				if (! funcp(sp, &newt, offset, &mytm, NULL))
 					continue;
 				if (tmcomp(&mytm, &yourtm) != 0)
 					continue;
@@ -2813,7 +2748,7 @@ time2sub(struct tm *const tmp,
 label:
 	if (increment_overflow_time_iinntt(&t, saved_seconds))
 		return WRONG;
-	if (funcp(sp, &t, offset, tmp))
+	if (funcp(sp, &t, offset, tmp, NULL))
 		*okayp = true;
 	return t;
 }
@@ -2821,7 +2756,7 @@ label:
 static time_t
 time2(struct tm * const	tmp,
      struct tm *funcp(struct state const *, time_t const *,
-		       int_fast32_t, struct tm *),
+		       int_fast32_t, struct tm *, time_t *),
      struct state const *sp,
      const int_fast32_t offset,
      bool *okayp)
@@ -2840,7 +2775,7 @@ time2(struct tm * const	tmp,
 static time_t
 time1(struct tm *const tmp,
      struct tm *funcp(struct state const *, time_t const *,
-		       int_fast32_t, struct tm *),
+		       int_fast32_t, struct tm *, time_t *),
      struct state const *sp,
      const int_fast32_t offset)
 {
@@ -255,6 +255,9 @@ strnlen (char const *s, size_t maxlen)
 #ifndef ENOMEM
 # define ENOMEM EINVAL
 #endif
+#ifndef ENOSYS
+# define ENOSYS EINVAL
+#endif
 #ifndef ENOTCAPABLE
 # define ENOTCAPABLE EINVAL
 #endif
@@ -264,6 +267,9 @@ strnlen (char const *s, size_t maxlen)
 #ifndef EOVERFLOW
 # define EOVERFLOW EINVAL
 #endif
+#ifndef EPERM
+# define EPERM EINVAL
+#endif

 #if HAVE_GETTEXT
 # include <libintl.h>
@@ -305,6 +311,7 @@ extern int optind;

 #ifndef HAVE_ISSETUGID
 # if (defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__ \
+      || defined __DragonFly__ \
      || (defined __linux__ && !defined __GLIBC__) /* Android, musl, etc. */ \
      || (defined __APPLE__ && defined __MACH__) || defined __sun)
 #  define HAVE_ISSETUGID 1
@@ -813,6 +820,7 @@ void tzset(void);
 # if (202311 <= __STDC_VERSION__ \
      || defined __GLIBC__ || defined __tm_zone /* musl */ \
      || defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__ \
+      || defined __DragonFly__ || defined __HAIKU__ \
      || (defined __APPLE__ && defined __MACH__))
 #  define HAVE_DECL_TIMEGM 1
 # else
@@ -841,7 +849,8 @@ extern char **environ;

 #ifndef HAVE_MEMPCPY
 # if (defined mempcpy \
-      || defined __FreeBSD__ || defined __NetBSD__ || defined __linux__)
+      || defined __FreeBSD__ || defined __NetBSD__ || defined __DragonFly__ \
+      || defined __linux__)
 #  define HAVE_MEMPCPY 1
 # else
 #  define HAVE_MEMPCPY 0
@@ -906,6 +915,7 @@ time_t posix2time(time_t);
     || defined __GLIBC__ \
     || defined __tm_zone /* musl */ \
     || defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__ \
+     || defined __DragonFly__ || defined __HAIKU__ \
     || (defined __APPLE__ && defined __MACH__))
 # if !defined TM_GMTOFF && !defined NO_TM_GMTOFF
 #  define TM_GMTOFF tm_gmtoff
@@ -1170,6 +1180,7 @@ enum {
 };

 #define isleap(y) (((y) % 4) == 0 && (((y) % 100) != 0 || ((y) % 400) == 0))
+#define year_days(y) (DAYSPERNYEAR + isleap(y))

 /*
 ** Since everything in isleap is modulo 400 (or a factor of 400), we know that
@@ -1183,6 +1194,6 @@ enum {
 ** We use this to avoid addition overflow problems.
 */

-#define isleap_sum(a, b)	isleap((a) % 400 + (b) % 400)
+#define year_sum_days(a, b) (DAYSPERNYEAR + isleap((a) % 400 + (b) % 400))

 #endif /* !defined PRIVATE_H */
@@ -464,9 +464,7 @@ label:
 						int	bot;
 						int	top;

-						len = isleap_sum(year, base) ?
-							DAYSPERLYEAR :
-							DAYSPERNYEAR;
+						len = year_sum_days(year, base);
 						/*
 						** What yday (-3 ... 3) does
 						** the ISO year begin on?
@@ -493,9 +491,8 @@ label:
 							break;
 						}
 						--base;
-						yday += isleap_sum(year, base) ?
-							DAYSPERLYEAR :
-							DAYSPERNYEAR;
+						yday += year_sum_days(year,
+								      base);
 					}
 #ifdef XPG4_1994_04_09
 					if ((w == 52 &&
@@ -12,6 +12,7 @@
 </head>

 <body>
+<main>
 <h1>Theory and pragmatics of the <code><abbr>tz</abbr></code> code and data</h1>
  <nav>
    <ul>
@@ -26,10 +27,10 @@
      <li><a href="#leapsec">Leap seconds</a></li>
      <li><a href="#calendar">Calendrical issues</a></li>
      <li><a href="#planets">Time and time zones off earth</a></li>
+      <li><a href="#see-also">See also</a></li>
    </ul>
  </nav>

-<section>
  <h2 id="scope">Scope of the <code><abbr>tz</abbr></code> database</h2>
 <p>
 The <a
@@ -112,9 +113,6 @@ It does not always make sense to talk about a timezone’s
 “base offset”, which is not necessarily a single number.
 </p>

-</section>
-
-<section>
  <h2 id="naming">Timezone identifiers</h2>
 <p>
 Each timezone has a name that uniquely identifies the timezone.
@@ -345,8 +343,7 @@ These legacy names are mostly defined in the file
 "<code>etcetera</code>".
 Also, the file "<code>backward</code>" defines the legacy names
 <code>Etc/GMT0</code>, <code>Etc/GMT-0</code>, <code>Etc/GMT+0</code>,
-<code>GMT0</code>, <code>GMT-0</code> and <code>GMT+0</code>,
-and the file "<code>northamerica</code>" defines the legacy names
+<code>GMT0</code>, <code>GMT-0</code>, <code>GMT+0</code>,
 <code>EST5EDT</code>, <code>CST6CDT</code>,
 <code>MST7MDT</code>, and <code>PST8PDT</code>.
 </li>
@@ -387,11 +384,11 @@ and <code>zone.tab</code>.

 <p>
 The database defines each timezone name to be a zone, or a link to a zone.
-The source file <code>backward</code> defines links for backward
-compatibility; it does not define zones.
+The source file <code>backward</code> defines links
+and a few zones for backward compatibility.
 Although <code>backward</code> was originally designed to be optional,
 nowadays distributions typically use it
-and no great weight should be attached to whether a link
+and no great weight should be attached to whether a link or zone
 is defined in <code>backward</code> or in some other file.
 The source file <code>etcetera</code> defines names that may be useful
 on platforms that do not support proleptic <code>TZ</code> strings
@@ -404,9 +401,7 @@ second information on platforms that support leap seconds.
 Another <code>etcetera</code> name, <code>GMT</code>,
 is used by older code releases.
 </p>
-</section>

-<section>
  <h2 id="abbreviations">Time zone abbreviations</h2>
 <p>
 When this package is installed, it generates time zone abbreviations
@@ -610,9 +605,7 @@ Israel.
 To avoid ambiguity, use numeric <abbr>UT</abbr> offsets like
 <code>-</code>0600 instead of time zone abbreviations like CST.
 </p>
-</section>

-<section>
  <h2 id="accuracy">Accuracy of the <code><abbr>tz</abbr></code> database</h2>
 <p>
 The <code><abbr>tz</abbr></code> database is not authoritative, and it
@@ -876,9 +869,7 @@ merely because two locations
 differ in <abbr>LMT</abbr> or transitioned to standard time at
 different dates.
 </p>
-</section>

-<section>
  <h2 id="functions">Time and date functions</h2>
 <p>
 The <code><abbr>tz</abbr></code> code contains time and date functions
@@ -1284,9 +1275,7 @@ The vestigial <abbr>API</abbr>s are:
    much the better.
  </li>
 </ul>
-</section>

-<section>
  <h2 id="stability">Interface stability</h2>
 <p>
 The <code><abbr>tz</abbr></code> code and data supply the following interfaces:
@@ -1353,9 +1342,7 @@ than Bangkok by putting <samp>Asia/Bangkok</samp> in the event’s record,
 the application should be robust in the presence of timezone splits
 between now and the future time.
 </p>
-</section>

-<section>
  <h2 id="leapsec">Leap seconds</h2>
 <p>
 Leap seconds were introduced in 1972 to accommodate the
@@ -1430,9 +1417,7 @@ Alternatively, you can install just one set of <abbr>TZif</abbr> files
 in the first place; see the <code>REDO</code> variable in this package’s
 <a href="https://en.wikipedia.org/wiki/Makefile">makefile</a>.
 </p>
-</section>

-<section>
  <h2 id="calendar">Calendrical issues</h2>
 <p>
 Calendrical issues are a bit out of scope for a time zone database,
@@ -1446,22 +1431,30 @@ Other information and sources are given in the file "<code>calendars</code>"
 in the <code><abbr>tz</abbr></code> distribution.
 They sometimes disagree.
 </p>
-</section>

-<section>
  <h2 id="planets">Time and time zones off Earth</h2>
 <p>
-The European Space Agency is <a
-href="https://www.esa.int/Applications/Satellite_navigation/Telling_time_on_the_Moon">considering</a>
-the establishment of a reference timescale for the Moon, which has
+Efforts are underway to establish a reference timescale for the Moon, which has
 days roughly equivalent to 29.5 Earth days, and where relativistic
 effects cause clocks to tick slightly faster than on Earth.
-Also, <abbr title="National Aeronautics and Space Administration">NASA</abbr>
-has been <a
+The European Space Agency <a
+href="https://www.esa.int/Applications/Satellite_navigation/Telling_time_on_the_Moon">began
+considering</a> the problem in 2023, and in 2024
+<abbr title="National Aeronautics and Space Administration">NASA</abbr>
+was <a
 href="https://bidenwhitehouse.archives.gov/wp-content/uploads/2024/04/Celestial-Time-Standardization-Policy.pdf">ordered</a>
 to consider the establishment of Coordinated Lunar Time (<abbr>LTC</abbr>).
-It is not yet known whether the US and European efforts will result in
-multiple timescales on the Moon.
+In 2025 a team at China’s
+<a href="https://en.wikipedia.org/wiki/Purple_Mountain_Observatory">Purple
+Mountain Observatory</a> published
+<a href="https://doi.org/10.1051/0004-6361/202557345">Lunar Time Ephemeris
+440</a>, the first formal proposal for a standard
+for Temps Coordonné Lunaire (<abbr>TCL</abbr>).
+A <a href="https://www.bipm.org/documents/20126/284836054/CGPM-2026-Draft-Resolutions.pdf">draft
+resolution of the 13–15 October 2026 General Conference on Weights
+and Measures</a> recommends that the <a href="https://www.bipm.org/en/">Bureau
+International des Poids et Mesures</a> collaborate with space agencies
+and other organizations on this matter.
 </p>

 <p>
@@ -1583,7 +1576,15 @@ Sources for time on other planets:
    (2016-01-20).
  </li>
 </ul>
-</section>
+</main>
+
+<aside>
+<h2 id="see-also">See also</h2>
+<ul>
+<li><a href="tz-link.html">Time zone and daylight saving time data</a></li>
+<li><a href="tz-art.html">Time and the arts</a></li>
+</ul>
+</aside>

 <footer>
 <hr>
@@ -9,6 +9,7 @@ ul {padding-left: 1.3rem;}
 <title>Time and the arts</title>
 </head>
 <body>
+<main>
 <h1>Time and the arts</h1>
 <h2>Documentaries</h2>
 <ul>
@@ -466,8 +467,10 @@ Unlike minimalism, it does not assume that the listener has plenty of time.
 <li>
 The webcomic <em>xkcd</em> has the strips
 “<a href="https://xkcd.com/673/">The Sun</a>” (2009-12-09),
-“<a href="https://xkcd.com/1655/">Doomsday Clock</a>” (2016-03-14) and
+“<a href="https://xkcd.com/1655/">Doomsday Clock</a>” (2016-03-14),
 “<a href="https://xkcd.com/2549/">Edge Cake</a>” (2021-12-01),
+“<a href="https://xkcd.com/2867/">DateTime</a>” (2023-12-13),
+and “<a href="https://xkcd.com/3272/">Time Change</a>” (2026-07-15),
 along with the panels
 “<a href="https://xkcd.com/448/">Good Morning</a>” (2008-07-11),
 “<a href="https://xkcd.com/1017/">Backward in Time</a>” (2012-02-14),
@@ -482,8 +485,7 @@ along with the panels
 “<a href="https://xkcd.com/2266/">Leap Smearing</a>” (2020-02-10),
 “<a href="https://xkcd.com/2594/">Consensus Time</a>” (2022-03-16),
 “<a href="https://xkcd.com/2846/">Daylight Saving Choice</a>” (2023-10-25),
-“<a href="https://xkcd.com/2854/">Date Line</a>” (2023-11-13),
-and “<a href="https://xkcd.com/2867/">DateTime</a>” (2023-12-13).
+and “<a href="https://xkcd.com/2854/">Date Line</a>” (2023-11-13).
 The related book <em>What If?</em> has an entry
 “<a href="https://what-if.xkcd.com/26/">Leap Seconds</a>” (2012-12-31).
 </li>
@@ -611,10 +613,16 @@ but maybe in your time zone I haven’t finished yet. So stay tuned!”
 (Goldie Hawn, <em>Rowan &amp; Martin’s Laugh-In</em> No. 65, 1970-03-09)
 </li>
 </ul>
+</main>
+
+<aside>
 <h2>See also</h2>
 <ul>
 <li><a href="tz-link.html">Time zone and daylight saving time data</a></li>
+<li><a href="theory.html">Theory and pragmatics of the
+<code><abbr>tz</abbr></code> code and data</a></li>
 </ul>
+</aside>

 <footer>
 <hr>
@@ -15,6 +15,7 @@ ul {padding-left: 1.3rem;}
 </style>
 </head>
 <body>
+<main>
 <h1>How to Read the <a href="https://en.wikipedia.org/wiki/Tz_database">tz
 Database</a> Source Files</h1>
 <h2>by Bill Seymour</h2>
@@ -415,17 +416,19 @@ Line.  For example:</p>

 <pre>
 #Zone NAME          STDOFF   RULES FORMAT [UNTIL]
-Zone America/Juneau 15:02:19 -     LMT    1867 Oct 18
+Zone America/Juneau 15:02:19 -     LMT    1867 Oct 19  0:31:13u
                    -8:57:41 -     LMT    ...
 </pre>

 <p>When Alaska was purchased from Russia in 1867, the Date Line moved
 from the Alaska/Canada border to the Bering Strait; and the time in
 Alaska was then 24 hours earlier than it had
-been. <code>&lt;aside&gt;</code>(6 October in the Julian calendar,
-which Russia was still using then for religious reasons, was followed
-by <i>a second instance of the same day with a different name</i>, 18
-October in the Gregorian calendar. Isn’t civil time
+been. <code>&lt;aside&gt;</code>(This also means that, although the sun had set
+on Friday 6 October and risen on Saturday 7 October in the Julian calendar,
+which Russia was still using then for religious reasons, upon the transfer
+Saturday afternoon became Friday afternoon, and then the sun set and rose once
+more on <i>second instances of the same days with different names</i>,
+Friday 18 and Saturday 19 October in the Gregorian calendar. Isn’t civil time
 wonderful? <code>8-)</code>)<code>&lt;/aside&gt;</code></p>

 <p>The abbreviation, “LMT” stands for “local mean
@@ -660,14 +663,15 @@ Zone Pacific/Honolulu -10:31:26 -     LMT    1896 Jan 13 12:00
 </table>

 <p>There will be a short quiz later. <code>8-)</code></p>
+</main>

+<footer>
 <hr>
-<address>
 This web page is in the public domain, so clarified as of
 2015-10-20 by Bill Seymour.
 <br>
 All suggestions and corrections will be welcome; all flames will be amusing.
 Mail to was at pobox dot com.
-</address>
+</footer>
 </body>
 </html>
@@ -11,6 +11,7 @@ ul {padding-left: 1.3rem;}
 </style>
 </head>
 <body>
+<main>
 <h1>Time zone and daylight saving time data</h1>
 <p>
 <a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and
@@ -61,7 +62,6 @@ area.
    </ul>
  </nav>

-<section>
 <h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2>
 <p>
 The <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a>
@@ -84,6 +84,7 @@ title="Berkeley Software Distribution">BSD</abbr></a>,
 <a href="https://netbsd.org">Net<abbr>BSD</abbr></a>,
 <a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>,
 <a href="https://www.chromium.org/chromium-os/">ChromiumOS</a>,
+<a href="https://en.wikipedia.org/wiki/OpenHarmony">OpenHarmony</a>,
 <a href="https://cygwin.com">Cygwin</a>,
 <a href="https://mariadb.org">MariaDB</a>,
 <a href="https://musl.libc.org">musl libc</a>,
@@ -133,9 +134,7 @@ Universal Time</a> (<abbr>UTC</abbr>).
 The database also records when daylight saving time was in use,
 along with some time zone abbreviations such as <abbr>EST</abbr>
 for Eastern Standard Time in the <abbr>US</abbr>.</p>
-</section>

-<section>
 <h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2>
 <p>
 The following <a
@@ -145,15 +144,15 @@ the latest release’s two
 to a <abbr>GNU</abbr>/Linux or similar host.</p>
 <pre><code>mkdir tzdb
 cd tzdb
-<a href="https://www.gnu.org/software/wget/">wget</a> https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz
-wget https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz
+<a href="https://www.gnu.org/software/wget/">wget</a> https://data.iana.org/time-zones/tzcode-latest.tar.gz
+wget https://data.iana.org/time-zones/tzdata-latest.tar.gz
 <a href="https://www.gnu.org/software/gzip/">gzip</a> -dc tzcode-latest.tar.gz | <a href="https://www.gnu.org/software/tar/">tar</a> -xf -
 gzip -dc tzdata-latest.tar.gz | tar -xf -
 </code></pre>
 <p>Alternatively, the following shell commands download the same
 release in a single-tarball format containing extra data
 useful for regression testing:</p>
-<pre><code>wget <a href="https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz">https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz</a>
+<pre><code>wget <a href="https://data.iana.org/time-zones/tzdb-latest.tar.lz">https://data.iana.org/time-zones/tzdb-latest.tar.lz</a>
 <a href="https://www.nongnu.org/lzip/">lzip</a> -dc tzdb-latest.tar.lz | tar -xf -
 </code></pre>
 <p>These commands use convenience links to the latest release
@@ -183,7 +182,7 @@ title="Hypertext Transfer Protocol Secure">HTTPS</abbr></a>,
 <a href="https://en.wikipedia.org/wiki/Rsync"><abbr
 title="remote sync">rsync</abbr></a>, and
 <a href="https://en.wikipedia.org/wiki/FTP"><abbr
-title="File Transfer Protocol">FTP</abbr></a>.
+title="File Transfer Protocol">FTP</abbr></a>.</p>
 <p>Alternatively, a development repository of code and data can be
 retrieved from <a href="https://github.com">GitHub</a> via the shell
 command:</p>
@@ -205,9 +204,7 @@ Time Zone Information Format (<abbr>TZif</abbr>)</a>
 The code also lets
 you read a <abbr>TZif</abbr> file and interpret timestamps for that
 location.</p>
-</section>

-<section>
 <h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2>
 <p>
 The <code><abbr>tz</abbr></code> code and data
@@ -234,7 +231,10 @@ the process by tailoring the generic instructions in
 the <code><abbr>tz</abbr> README</code> file and installing the latest
 data yourself. System-specific instructions for installing the
 latest <code><abbr>tz</abbr></code> data have also been published
-for <a href="https://www.ibm.com/support/pages/aix-time-zone-olson-tzdata-updates"><abbr>AIX</abbr></a>,
+for <a href="https://community.ibm.com/community/user/blogs/ravindra-shinde/2024/12/13/time-zone-update-tool-tz"><abbr>AIX</abbr></a>
+(and
+<a href="https://www.ibm.com/support/pages/aix-time-zone-olson-tzdata-updates">older
+<abbr>AIX</abbr></a>),
 <a
 href="https://source.android.com/docs/core/permissions/timezone-rules">Android</a>,
 <a
@@ -276,16 +276,14 @@ found in <a href="theory.html">Theory and pragmatics of the
 <a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a>
 displays changes between recent <code><abbr>tzdb</abbr></code> versions.
 </p>
-</section>

-<section>
 <h2 id="coordinating">Coordinating with governments and distributors</h2>
 <p>
 As discussed in
 “<a href="https://www.icann.org/en/blogs/details/how-time-zones-are-coordinated-13-03-2023-en">How
 Time Zones Are Coordinated</a>”, the time zone database relies on
 collaboration among governments, the time zone database volunteer
-community, and data distributors downstream.
+community, and data distributors downstream.</p>
 <p>
 If your government plans to change its time zone boundaries or
 daylight saving rules, please send email as described in
@@ -326,9 +324,7 @@ The shorter the notice, the more likely clock problems will arise; see “<a
 href="https://codeofmatt.com/on-the-timing-of-time-zone-changes/">On
 the Timing of Time Zone Changes</a>” for examples.
 </p>
-</section>

-<section>
 <h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2>
 <ul>
 <li>The article
@@ -344,9 +340,7 @@ database’s style.</li>
 <li><a href="https://doi.org/10.1145/3340301.3341125">What time is it:
 managing time in the internet</a> analyzes the database longitudinally.</li>
 </ul>
-</section>

-<section>
 <h2 id="web">Web sites using recent versions of the
 <code><abbr>tz</abbr></code> database</h2>
 <p>
@@ -380,9 +374,7 @@ calculates the current time difference between locations.</li>
 <li><a href="https://www.wx-now.com">Weather Now</a> and
 <a href="https://www.thetimenow.com">The Time Now</a> list the weather too.</li>
 </ul>
-</section>

-<section>
 <h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2>
 <ul>
 <li><a href="https://www.rfc-editor.org/info/rfc7808/">Time Zone
@@ -405,9 +397,7 @@ title="Extensible Markup Language">XML</abbr></a> format, and a variant
 uses <a href="https://www.json.org/json-en.html"><abbr
 title="JavaScript Object Notation">JSON</abbr></a> format.</li>
 </ul>
-</section>

-<section>
 <h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2>
 <p>Although some of these do not fully support
 <code><abbr>tz</abbr></code> data, in recent <code><abbr>tzdb</abbr></code>
@@ -416,7 +406,7 @@ running the command <code>make rearguard_tarballs</code> and compiling
 from the resulting tarballs instead.</p>
 <ul>
 <li><a href="https://github.com/libical">Libical</a>
-contains <code>vzic</code>, <a
+contains <code>vzic</code>, a <a
 href="https://en.wikipedia.org/wiki/C_(programming_language)">C</a>
 program that compiles
 <code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files.
@@ -425,6 +415,23 @@ available under the <a
 href="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr>
 General Public License (<abbr
 title="General Public License">GPL</abbr>)</a>.</li>
+<li>The <a id="TZDP"
+href="https://howardhinnant.github.io/date/tz.html">Time Zone
+Database Parser</a> contains a
+<a href="https://en.wikipedia.org/wiki/C++">C++</a> runtime parser
+supporting the <a
+href="https://en.cppreference.com/cpp/chrono#Time_zone"><code>std::chrono::time_zone</code> API</a>
+that is standardized in
+<a href="https://en.wikipedia.org/wiki/C%2B%2B20">C++20</a> and later.
+It is freely available under the
+<a href="https://en.wikipedia.org/wiki/MIT_License"><abbr
+title="Massachusetts Institute of Technology">MIT</abbr> license</a>.
+This approach is used by the <code>std::chrono::time_zone</code> implementation
+of <a href="https://gcc.gnu.org/"><abbr
+title="the GNU Compiler Collection">GCC</abbr></a>
+<code>libstdc++</code>, which is available under the GPL combined
+with the <a href="https://www.gnu.org/licenses/gcc-exception.html">GCC
+Runtime Library Exception</a>.</li>
 <li><a
 href="https://metacpan.org/release/DateTime-TimeZone">DateTime::TimeZone</a>
 contains a script <code>parse_olson</code> that compiles
@@ -436,14 +443,6 @@ available under both the <abbr>GPL</abbr> and the Perl Artistic
 License. DateTime::TimeZone also contains a script
 <code>tests_from_zdump</code> that generates test cases for each clock
 transition in the <code><abbr>tz</abbr></code> database.</li>
-<li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone
-Database Parser</a> is a
-<a href="https://en.wikipedia.org/wiki/C++">C++</a> parser and
-runtime library with a <a
-href="https://en.cppreference.com/cpp/chrono"><code>std::chrono</code> API</a>
-that is a standard part of C++.
-It is freely available under the
-<abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>
 <li><a id="ICU" href="https://icu.unicode.org">International Components for
 Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a
 href="https://en.wikipedia.org/wiki/Java_(programming_language)">Java</a>
@@ -498,6 +497,7 @@ License">LGPL</abbr>)</a>.</li>
 <li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and
 Java-based libraries.</li>
 </ul>
+</li>
 <li><a href="https://nodatime.org">Noda Time – Date and
 time <abbr>API</abbr> for .NET</a>
 is like Joda-Time and Time4J, but for the .NET framework instead of Java.
@@ -549,6 +549,7 @@ objects</a> let programs access an abstract view of
 <code><abbr>tzdb</abbr></code> data, and are designed to replace <a
 href="https://codeofmatt.com/javascript-date-type-is-horribly-broken/">JavaScript’s
 problematic <code>Date</code> objects</a> when working with dates and times.
+</li>
 <li><a href="https://github.com/JuliaTime">JuliaTime</a> contains a
 compiler from <code><abbr>tz</abbr></code> source into
 <a href="https://julialang.org">Julia</a>. It is freely available
@@ -587,9 +588,7 @@ source into text files, along with a runtime that can read those
 files. Tcl is freely available under a <abbr>BSD</abbr>-style
 license.</li>
 </ul>
-</section>

-<section>
 <h2 id="TZif">Other <abbr>TZif</abbr> readers</h2>
 <ul>
 <li>The <a
@@ -604,6 +603,17 @@ a <abbr>TZif</abbr> file reader written in C that
 creates a <code>GTimeZone</code> object representing sets
 of <abbr>UT</abbr> offsets.
 It is freely available under the <abbr>LGPL</abbr>.</li>
+<li>The <a href="https://en.wikipedia.org/wiki/Musl">musl</a> C library
+also has an <abbr>TZif</abbr> reader.
+It is freely available under the <abbr>MIT</abbr> license.</li>
+<li>The Time Zone Database Parser for C++, mentioned <a href="#TZDP">above,</a>
+can be configured to read TZif binary files.
+A similar approach is taken in
+<a href="https://www.llvm.org/"><abbr>LLVM</abbr></a>
+<code>std::chrono::time_zone</code>, which is available
+under the Apache License with
+<a href="https://llvm.org/docs/DeveloperPolicy.html#open-source-licensing-terms">LLVM
+Exceptions</a>.</li>
 <li>The
 <a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>’s
 <code>baltzo::TimeZoneUtil</code> component contains a C++
@@ -659,15 +669,20 @@ converts <abbr>TZif</abbr> data into
 <abbr>JSON</abbr>-format data suitable for use
 in its JavaScript library for time zone conversion. Dates before 1970
 are not supported.</li>
+<li>The <a href="https://crates.io/crates/jiff">jiff</a> datetime library
+for <a href="https://rust-lang.org/">Rust</a> either compiles
+<code><abbr>tz</abbr></code> source into Rust,
+or consults <abbr>TZif</abbr> data at runtime.
+It is in the public domain.
+It intends to supplant the soft-deprecated
+<a href="https://crates.io/crates/chrono-tz">Chrono-TZ</a>.</li>
 <li>The <a
 href="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a>
 package contains <a href="https://www.haskell.org">Haskell</a> code that
 parses and uses <abbr>TZif</abbr> data. It is freely
 available under a <abbr>BSD</abbr>-style license.</li>
 </ul>
-</section>

-<section>
 <h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2>
 <ul>
 <li><a href="https://foxclocks.org">FoxClocks</a>
@@ -684,7 +699,10 @@ data (mentioned <a href="#CLDR">below</a>) used by the
 <a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> /
 <a href="https://en.wikipedia.org/wiki/Universal_Windows_Platform">Universal Windows Platform</a> classes
 <a href="https://learn.microsoft.com/en-us/uwp/api/Windows.Globalization.DateTimeFormatting.DateTimeFormatter"><code>DateTimeFormatter</code></a> and
-<a href="https://learn.microsoft.com/en-us/uwp/api/windows.globalization.calendar"><code>Calendar</code></a>.
+<a href="https://learn.microsoft.com/en-us/uwp/api/windows.globalization.calendar"><code>Calendar</code></a>,
+and with updates discussed in the
+<a href="https://techcommunity.microsoft.com/category/windows/blog/dstblog">Daylight
+Saving Time &amp; Time Zone Blog</a>.
 <a id="System.TimeZoneInfo"
 href="https://learn.microsoft.com/en-us/archive/blogs/bclteam/exploring-windows-time-zones-with-system-timezoneinfo-josh-free">Exploring
 Windows Time Zones with <code>System.TimeZoneInfo</code></a> describes
@@ -700,16 +718,14 @@ to <code><abbr>tz</abbr></code> names.
 These mappings can be performed programmatically via the
 <a href="https://github.com/mattjohnsonpint/TimeZoneConverter">TimeZoneConverter</a>
 .NET library,
-or the ICU Java and C++ libraries mentioned <a href="#ICU">above</a>.
+or the ICU Java and C++ libraries mentioned <a href="#ICU">above</a>.</li>
 <li><a
 href="https://www.oracle.com/java/">Oracle
 Java</a> contains a copy of a subset of a recent
 <code><abbr>tz</abbr></code> database in a
 Java-specific format.</li>
 </ul>
-</section>

-<section>
 <h2 id="other-dbs">Other time zone databases</h2>
 <ul>
 <li><a href="https://www.astro.com/atlas">Time-zone Atlas</a>
@@ -733,9 +749,7 @@ Schedules Information Manual</a> of the
 International Air Transport Association
 gives current time zone rules for airports served by commercial aviation.</li>
 </ul>
-</section>

-<section>
 <h2 id="maps">Maps</h2>
 <ul>
 <li><a href="https://www.worldtimezone.com">World Time Zone Map
@@ -757,9 +771,7 @@ World Factbook</em></a>, formerly published by the
 Although the maps’ pictorial quality is good,
 the maps do not indicate daylight saving time.</li>
 </ul>
-</section>

-<section>
 <h2 id="boundaries">Time zone boundaries</h2>
 <p>Geographical boundaries between timezones are available
 from several <a
@@ -810,9 +822,7 @@ for land and territorial waters only). A captain can change ship’s
 clocks any time after entering a new time zone; midnight changes are
 common.</li>
 </ul>
-</section>

-<section>
 <h2 id="civil">Civil time concepts and history</h2>
 <ul>
 <li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time">A
@@ -835,9 +845,7 @@ time zone boundary.</li>
 <li><a href="https://statoids.com/tconcept.html">Basic Time
 Zone Concepts</a> discusses terminological issues behind time zones.</li>
 </ul>
-</section>

-<section>
 <h2 id="national">National histories of legal time</h2>
 <dl>
 <dt>Australia</dt>
@@ -935,9 +943,7 @@ Navy (SOHMA) publishes an annual <a
 href="https://sohma.armada.mil.uy/index.php/servicios/datos-astronomicos" hreflang="es">almanac
 (in Spanish)</a>.</dd>
 </dl>
-</section>

-<section>
 <h2 id="costs">Costs and benefits of time shifts</h2>
 <p>Various sources argue for and against daylight saving time and time
 zone shifts, and many scientific studies have been conducted. This
@@ -1016,9 +1022,7 @@ opposes <abbr>DST</abbr> changes and permanent <abbr>DST</abbr>,
 and advocates that governments adopt
 “permanent Standard Time for the health and safety of their citizens”.</li>
 </ul>
-</section>

-<section>
 <h2 id="precision">Precision timekeeping</h2>
 <ul>
 <li><a
@@ -1053,7 +1057,7 @@ a client’s time zone and daylight saving settings automatically.</li>
 Scales</a> describes astronomical time scales like
 <abbr title="Terrestrial Dynamic Time">TDT</abbr>,
 <abbr title="Geocentric Coordinate Time">TCG</abbr>, and
-<abbr title="Barycentric Dynamic Time">TDB</abbr>.
+<abbr title="Barycentric Dynamic Time">TDB</abbr>.</li>
 <li>The <a href="https://www.iau.org"><abbr
 title="International Astronomical Union">IAU</abbr></a>’s <a
 href="https://www.iausofa.org"><abbr
@@ -1170,9 +1174,7 @@ However, there is still no consensus on whether this is the best way
 to replace leap seconds.
 </li>
 </ul>
-</section>

-<section>
 <h2 id="notation">Time notation</h2>
 <ul>
 <li>The <a id="CLDR" href="https://cldr.unicode.org">Unicode Common Locale Data
@@ -1183,7 +1185,7 @@ contains French translations for “Eastern European Summer Time”,
 <a href="https://unicode.org/cldr/charts/latest/by_type/">by-type
 charts</a> show these values for many locales. Data values are available in
 both <abbr title="Locale Data Markup Language">LDML</abbr>
-(an <abbr>XML</abbr> format) and <abbr>JSON</abbr>.
+(an <abbr>XML</abbr> format) and <abbr>JSON</abbr>.</li>
 <li>
 <a href="https://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of
 the international standard date and time notation</a> covers
@@ -1209,7 +1211,7 @@ An extension, <a href="https://www.rfc-editor.org/info/rfc9557/">Date
 and Time on the Internet: Timestamps with Additional Information</a>
 (Internet <abbr>RFC</abbr> 9557) extends this profile
 to let you specify the <code><abbr>tzdb</abbr></code> timezone of a timestamp
-via suffixes like <code>[Asia/Tokyo]</code>.
+via suffixes like <code>[Asia/Tokyo]</code>.</li>
 <li>
 <a href="https://web.archive.org/web/20190130042457/https://www.hackcraft.net/web/datetime/">Date &amp; Time
 Formats on the Web</a> surveys web- and Internet-oriented date and time
@@ -1243,16 +1245,16 @@ any future changes to the rules. One should never set
 local time is nine hours ahead of <abbr>UT</abbr> and the time zone
 is called “<abbr>GMT</abbr>”.</li>
 </ul>
-</section>
+</main>

-<section>
+<aside>
 <h2 id="see-also">See also</h2>
 <ul>
 <li><a href="theory.html">Theory and pragmatics of the
 <code><abbr>tz</abbr></code> code and data</a></li>
 <li><a href="tz-art.html">Time and the arts</a></li>
 </ul>
-</section>
+</aside>

 <footer>
 <hr>
@@ -402,7 +402,6 @@ SEE ALSO
       time(2), localtime(3), tzset(3), tzselect(8), zdump(8), zic(8).

       Olson A, Eggert P, Murchison K. The Time Zone Information Format
-       (TZif).  October 2024.  Internet RFC 9636 ⟨https://www.rfc-editor.org/
-       rfc/rfc9636⟩ doi:10.17487/RFC9636 ⟨https://doi.org/10.17487/RFC9636⟩.
+       (TZif).  October 2024.  Internet RFC 9636 doi:10.17487/RFC9636.

 Time Zone Database                                                   tzfile(5)
@@ -1 +1 @@
-2026c
+2026d
@@ -719,7 +719,7 @@ delta_nonneg(struct tm *newp, struct tm *oldp)
 	intmax_t sec = SECSPERREPEAT, result = cycles * sec;
 	int tmy = oldp->tm_year + cycles * YEARSPERREPEAT;
 	for ( ; tmy < newp->tm_year; ++tmy)
-		result += DAYSPERNYEAR + isleap_sum(tmy, TM_YEAR_BASE);
+	  result += year_sum_days(tmy, TM_YEAR_BASE);
 	result += newp->tm_yday - oldp->tm_yday;
 	result *= HOURSPERDAY;
 	result += newp->tm_hour - oldp->tm_hour;
@@ -746,7 +746,7 @@ adjusted_yday(struct tm const *a, struct tm const *b)
 {
  int yday = a->tm_yday;
  if (b->tm_year < a->tm_year)
-    yday += 365 + isleap_sum(b->tm_year, TM_YEAR_BASE);
+    yday += year_sum_days(b->tm_year, TM_YEAR_BASE);
  return yday;
 }
 #endif
@@ -330,12 +330,8 @@ for the
 POSIX Portable Character Set (PPCS)
 .UE
 and the encoding's non-unibyte characters should consist entirely of
-non-PPCS bytes.  Non-PPCS characters typically occur only in comments:
-although output file names and time zone abbreviations can contain
-nearly any character, other software will work better if these are
-limited to the restricted syntax described under the
-.B \-v
-option.
+non-PPCS bytes.
+Non-PPCS characters typically occur only in comments.
 .PP
 Input lines are made up of fields.
 Fields are separated from one another by one or more white space characters.
@@ -350,15 +346,16 @@ Any line that is blank (after comment stripping) is ignored.
 Nonblank lines are expected to be of one of three types:
 rule lines, zone lines, and link lines.
 .PP
-Names must be in English and are case insensitive.
+Keywords are in English and are case insensitive.
+They are not reserved words.
 They appear in several contexts, and include month and weekday names
-and keywords such as
+and other words such as
 .BR "maximum" ,
 .BR "only" ,
 .BR "Rolling" ,
 and
 .BR "Zone" .
-A name can be abbreviated by omitting all but an initial prefix; any
+A keyword can be abbreviated by omitting all but an initial prefix; any
 abbreviation must be unambiguous in context.
 .PP
 A rule line has the form
@@ -586,11 +583,26 @@ The name of the timezone.
 This is the name used in creating the time conversion information file for the
 timezone.
 It should not contain a file name component
+that is empty or is
 .q ".\&"
 or
 .q ".." ;
 a file name component is a maximal substring that does not contain
 .q "/" .
+Names can be further restricted by the operating system or file system.
+Most systems reject a name
+.IB A / B
+if there is another name
+.IR A ,
+some reject names differing only in case,
+and some reject names containing special characters like
+.q ":"
+and
+.q "\e" .
+Other software will work better if names are
+limited to the restricted syntax described under the
+.B \-v
+option.
 .TP
 .B STDOFF
 The amount of time to add to UT to get standard time,
@@ -737,8 +749,16 @@ A link line has the form
 .ta \w'Link\0\0'u +\w'Europe/Istanbul\0\0'u
 Link	TARGET	LINK-NAME
 .sp
+.fi
+where
+.B TARGET
+and
+.B LINK-NAME
+both have the same syntax as a zone line's
+.BR NAME .
 For example:
 .sp
+.nf
 .ti +2
 Link	Europe/Istanbul	Asia/Istanbul
 .sp
@@ -752,10 +772,7 @@ field in some zone line or as the
 field in some link line.
 The
 .B LINK-NAME
-field is used as an alternative name for that zone;
-it has the same syntax as a zone line's
-.B NAME
-field.
+field is an alternative name for that zone.
 Links can chain together, although the behavior is unspecified if a
 chain of one or more links does not terminate in a Zone name.
 A link line can appear before the line that defines the link target.
@@ -186,13 +186,9 @@ FILES
       zero or more lines, each ending in a newline byte and containing at
       most 2048 bytes counting the newline, and without any NUL bytes.  The
       input text's encoding is typically UTF-8 or ASCII; it should have a
-       unibyte representation for the POSIX Portable Character Set (PPCS)
-       ⟨https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap06
-       .html⟩ and the encoding's non-unibyte characters should consist
-       entirely of non-PPCS bytes.  Non-PPCS characters typically occur only
-       in comments: although output file names and time zone abbreviations can
-       contain nearly any character, other software will work better if these
-       are limited to the restricted syntax described under the -v option.
+       unibyte representation for the POSIX Portable Character Set (PPCS) and
+       the encoding's non-unibyte characters should consist entirely of non-
+       PPCS bytes.  Non-PPCS characters typically occur only in comments.

       Input lines are made up of fields.  Fields are separated from one
       another by one or more white space characters.  The white space
@@ -206,11 +202,11 @@ FILES
       lines are expected to be of one of three types: rule lines, zone lines,
       and link lines.

-       Names must be in English and are case insensitive.  They appear in
-       several contexts, and include month and weekday names and keywords such
-       as maximum, only, Rolling, and Zone.  A name can be abbreviated by
-       omitting all but an initial prefix; any abbreviation must be
-       unambiguous in context.
+       Keywords are in English and are case insensitive.  They are not
+       reserved words.  They appear in several contexts, and include month and
+       weekday names and other words such as maximum, only, Rolling, and Zone.
+       A keyword can be abbreviated by omitting all but an initial prefix; any
+       abbreviation must be unambiguous in context.

       A rule line has the form

@@ -330,8 +326,14 @@ FILES

       NAME   The name of the timezone.  This is the name used in creating the
              time conversion information file for the timezone.  It should
-              not contain a file name component “.” or “..”; a file name
-              component is a maximal substring that does not contain “/”.
+              not contain a file name component that is empty or is “.” or
+              “..”; a file name component is a maximal substring that does not
+              contain “/”.  Names can be further restricted by the operating
+              system or file system.  Most systems reject a name A/B if there
+              is another name A, some reject names differing only in case, and
+              some reject names containing special characters like “:” and
+              “\”.  Other software will work better if names are limited to
+              the restricted syntax described under the -v option.

       STDOFF The amount of time to add to UT to get standard time, without
              any adjustment for daylight saving.  This field has the same
@@ -418,17 +420,17 @@ FILES

         Link  TARGET           LINK-NAME

-       For example:
+       where TARGET and LINK-NAME both have the same syntax as a zone line's
+       NAME.  For example:

         Link  Europe/Istanbul  Asia/Istanbul

       The TARGET field should appear as the NAME field in some zone line or
-       as the LINK-NAME field in some link line.  The LINK-NAME field is used
-       as an alternative name for that zone; it has the same syntax as a zone
-       line's NAME field.  Links can chain together, although the behavior is
-       unspecified if a chain of one or more links does not terminate in a
-       Zone name.  A link line can appear before the line that defines the
-       link target.  For example:
+       as the LINK-NAME field in some link line.  The LINK-NAME field is an
+       alternative name for that zone.  Links can chain together, although the
+       behavior is unspecified if a chain of one or more links does not
+       terminate in a Zone name.  A link line can appear before the line that
+       defines the link target.  For example:

         Link  Greenwich  G_M_T
         Link  Etc/GMT    Greenwich
@@ -528,10 +528,6 @@ static const int	len_months[2][MONSPERYEAR] = {
 	{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
 };

-static const int	len_years[2] = {
-	DAYSPERNYEAR, DAYSPERLYEAR
-};
-
 static struct attype {
 	zic_t		at;
 	bool		dontmerge;
@@ -783,6 +779,7 @@ arg2num(char const *arg, int base, unsigned long maxval, char const *msgid)

 #ifndef HAVE_SETMODE
 # if (defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__ \
+      || defined __DragonFly__ \
      || (defined __APPLE__ && defined __MACH__))
 #  define HAVE_SETMODE 1
 # else
@@ -1467,6 +1464,12 @@ namecheck(const char *name)
 	register char const *component = name;
 	for (cp = name; *cp; cp++) {
 		unsigned char c = *cp;
+#if defined _WIN32 || defined __CYGWIN__
+		if (c == ':' || c == '\\') {
+		  error(N_("file name '%s' contains '%c'"), name, c);
+		  return false;
+		}
+#endif
 		if (noise && !strchr(benign, c)) {
 			warning((strchr(printable_and_not_benign, c)
 				 ? N_("file name '%s' contains byte '%c'")
@@ -1781,8 +1784,20 @@ dolink(char const *target, char const *linkname, bool staysymlink)
 	      break;
 	    }
 	    link_errno = errno;
+	    /* When hard links are not supported, some MS-Windows file system
+	       drivers fail with EINVAL, contrary to the intent of
+	       MS-FSA 42.0 (2025) section 2.1.5.15.7.  */
+	    if (link_errno == EINVAL)
+	      link_errno = ENOTSUP;
 	  }
 #endif
+	  /* On platforms like AIX, the Linux kernel, macOS, and Solaris,
+	     link/linkat can fail with ENOSYS or EPERM if the file system
+	     does not support hard links, or if other problems occur.
+	     It is too much trouble to suss out the other problems.  */
+	  if (link_errno == ENOSYS || link_errno == EPERM)
+	    link_errno = ENOTSUP;
+
 	  if (link_errno == EXDEV || link_errno == ENOTSUP)
 	    break;

@@ -1849,7 +1864,8 @@ dolink(char const *target, char const *linkname, bool staysymlink)
 		      strerror(link_errno));
 	    else if (symlink_errno < 0)
 	      warning(N_("copy used because symbolic link not obvious"));
-	    else if (symlink_errno != ENOTSUP)
+	    else if (symlink_errno != ENOSYS && symlink_errno != ENOTSUP
+		     && symlink_errno != EPERM)
 	      warning(N_("copy used because symbolic link failed: %s"),
 		      strerror(symlink_errno));
 	  }
@@ -2307,18 +2323,13 @@ inzsub(char **fields, int nfields, bool iscont)
 static zic_t
 getleapdatetime(char **fields, bool expire_line)
 {
-	register const char *		cp;
 	register const struct lookup *	lp;
-	register zic_t			i, j;
 	zic_t				year;
-	int				month, day;
-	zic_t				dayoff, tod;
 	zic_t				t;
 	char xs;
+	struct rule r;

-	dayoff = 0;
-	cp = fields[LP_YEAR];
-	if (sscanf(cp, "%"SCNdZIC"%c", &year, &xs) != 1) {
+	if (sscanf(fields[LP_YEAR], "%"SCNdZIC"%c", &year, &xs) != 1) {
 		/*
 		** Leapin' Lizards!
 		*/
@@ -2332,38 +2343,20 @@ getleapdatetime(char **fields, bool expire_line)
 		leapminyear = year;
 	    leapseen = true;
 	}
-	j = EPOCH_YEAR;
-	while (j != year) {
-		if (year > j) {
-			i = len_years[isleap(j)];
-			++j;
-		} else {
-			--j;
-			i = -len_years[isleap(j)];
-		}
-		dayoff = oadd(dayoff, i);
-	}
 	if ((lp = byword(fields[LP_MONTH], mon_names)) == NULL) {
 		error(N_("invalid month name"));
 		return -1;
 	}
-	month = lp->l_value;
-	j = TM_JANUARY;
-	while (j != month) {
-		i = len_months[isleap(year)][j];
-		dayoff = oadd(dayoff, i);
-		++j;
-	}
-	cp = fields[LP_DAY];
-	if (sscanf(cp, "%d%c", &day, &xs) != 1 ||
-		day <= 0 || day > len_months[isleap(year)][month]) {
+	r.r_month = lp->l_value;
+	if (! (sscanf(fields[LP_DAY], "%d%c", &r.r_dayofmonth, &xs) == 1
+	       && 0 < r.r_dayofmonth
+	       && r.r_dayofmonth <= len_months[isleap(year)][r.r_month])) {
 			error(N_("invalid day of month"));
 			return -1;
 	}
-	dayoff = oadd(dayoff, day - 1);
-	t = omul(dayoff, SECSPERDAY);
-	tod = gethms(fields[LP_TIME], N_("invalid time of day"));
-	t = tadd(t, tod);
+	r.r_dycode = DC_DOM;
+	r.r_tod = gethms(fields[LP_TIME], N_("invalid time of day"));
+	t = rpytime(&r, year);
 	if (t < 0)
 	  error(N_("leap second precedes Epoch"));
 	return t;
@@ -2419,6 +2412,8 @@ inlink(char **fields, int nfields)
 		error(N_("blank TARGET field on Link line"));
 		return;
 	}
+	if (! namecheck(fields[LF_TARGET]))
+	  return;
 	if (! namecheck(fields[LF_LINKNAME]))
 	  return;
 	l.l_filenum = filenum;
@@ -3552,10 +3547,13 @@ outzone(const struct zone *zpfirst, ptrdiff_t zonecount)
 			} else
 				defaulttype = type;
 		} else {
-		  zic_t year;
-		  for (year = min_year; year <= max_year; ++year) {
+		  zic_t year, next_year;
+		  bool try_next_year = true;
+		  for (year = min_year; try_next_year; year = next_year) {
 			if (useuntil && year > zp->z_untilrule.r_hiyear)
 				break;
+			try_next_year = false;
+			next_year = max_year;
 			/*
 			** Mark which rules to do in the current year.
 			** For those to do, calculate rpytime(rp, year);
@@ -3567,6 +3565,17 @@ outzone(const struct zone *zpfirst, ptrdiff_t zonecount)
 				struct rule *rp = &zp->z_rules[j];
 				eats(zp->z_filenum, zp->z_linenum,
 				     rp->r_filenum, rp->r_linenum);
+
+				/* Keep track of the earliest year after YEAR
+				   in which some rule <= J applies.  */
+				if (year < rp->r_hiyear) {
+				  zic_t next = max(year + 1, rp->r_loyear);
+				  if (next <= next_year) {
+				    next_year = next;
+				    try_next_year = true;
+				  }
+				}
+
 				rp->r_todo = year >= rp->r_loyear &&
 						year <= rp->r_hiyear;
 				if (rp->r_todo) {
@@ -4147,7 +4156,7 @@ rpytime(const struct rule *rp, zic_t wantedy)
 	wantedy = y + (yrem + 2 * YEARSPERREPEAT) % YEARSPERREPEAT;

 	while (wantedy != y) {
-		i = len_years[isleap(y)];
+		i = year_days(y);
 		dayoff = oadd(dayoff, i);
 		y++;
 	}
@@ -1 +1 @@
 c
 d