From: DJ Delorie <dj@redhat.com>
To: libc-stable@sourceware.org
Subject: [COMMITTED 2.26] mktime: improve heuristic for ca-1986 Indiana DST
Date: Wed, 09 Nov 2022 14:36:39 -0500 [thread overview]
Message-ID: <xnwn833ooo.fsf@greed.delorie.com> (raw)
This patch syncs mktime.c from Gnulib, fixing a
problem reported by Mark Krenz <https://bugs.gnu.org/48085>,
and it should fix BZ#29035 too.
* time/mktime.c (__mktime_internal): Be more generous about
accepting arguments with the wrong value of tm_isdst, by falling
back to a one-hour DST difference if we find no nearby DST that is
unusual. This fixes a problem where "1986-04-28 00:00 EDT" was
rejected when TZ="America/Indianapolis" because the nearest DST
timestamp occurred in 1970, a temporal distance too great for the
old heuristic. This also also narrows the search a bit, which
is a minor performance win.
(cherry picked from commit 83859e1115269cf56d21669361d4ddbe2687831c)
diff --git a/time/mktime.c b/time/mktime.c
index 494c89bf54..e9a6006710 100644
--- a/time/mktime.c
+++ b/time/mktime.c
@@ -429,8 +429,13 @@ __mktime_internal (struct tm *tp,
time with the right value, and use its UTC offset.
Heuristic: probe the adjacent timestamps in both directions,
- looking for the desired isdst. This should work for all real
- time zone histories in the tz database. */
+ looking for the desired isdst. If none is found within a
+ reasonable duration bound, assume a one-hour DST difference.
+ This should work for all real time zone histories in the tz
+ database. */
+
+ /* +1 if we wanted standard time but got DST, -1 if the reverse. */
+ int dst_difference = (isdst == 0) - (tm.tm_isdst == 0);
/* Distance between probes when looking for a DST boundary. In
tzdata2003a, the shortest period of DST is 601200 seconds
@@ -441,12 +446,14 @@ __mktime_internal (struct tm *tp,
periods when probing. */
int stride = 601200;
- /* The longest period of DST in tzdata2003a is 536454000 seconds
- (e.g., America/Jujuy starting 1946-10-01 01:00). The longest
- period of non-DST is much longer, but it makes no real sense
- to search for more than a year of non-DST, so use the DST
- max. */
- int duration_max = 536454000;
+ /* In TZDB 2021e, the longest period of DST (or of non-DST), in
+ which the DST (or adjacent DST) difference is not one hour,
+ is 457243209 seconds: e.g., America/Cambridge_Bay with leap
+ seconds, starting 1965-10-31 00:00 in a switch from
+ double-daylight time (-05) to standard time (-07), and
+ continuing to 1980-04-27 02:00 in a switch from standard time
+ (-07) to daylight time (-06). */
+ int duration_max = 457243209;
/* Search in both directions, so the maximum distance is half
the duration; add the stride to avoid off-by-1 problems. */
@@ -483,6 +490,11 @@ __mktime_internal (struct tm *tp,
}
}
+ /* No unusual DST offset was found nearby. Assume one-hour DST. */
+ t += 60 * 60 * dst_difference;
+ if (mktime_min <= t && t <= mktime_max && convert_time (convert, t, &tm))
+ goto offset_found;
+
__set_errno (EOVERFLOW);
return -1;
}
reply other threads:[~2022-11-09 19:36 UTC|newest]
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