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authorPaul Eggert <eggert@cs.ucla.edu>2022-09-08 20:08:32 -0500
committerPaul Eggert <eggert@cs.ucla.edu>2022-09-08 22:55:54 -0500
commit83859e1115269cf56d21669361d4ddbe2687831c (patch)
tree39a225e7d9bea9a0eccdbbe075faf03de61f75b2 /time
parent82a1ec851025ccae54dea43149915707f890746b (diff)
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mktime: improve heuristic for ca-1986 Indiana DST
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.
Diffstat (limited to 'time')
-rw-r--r--time/mktime.c28
1 files changed, 20 insertions, 8 deletions
diff --git a/time/mktime.c b/time/mktime.c
index aa12e28..7dc9d67 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;
}