1 files changed, 21 insertions, 9 deletions

diff --git a/gl/mktime.c b/gl/mktime.c
index ae721c72..7dc9d67e 100644
--- a/gl/mktime.c
+++ b/gl/mktime.c
@@ -1,5 +1,5 @@
 /* Convert a 'struct tm' to a time_t value.
-   Copyright (C) 1993-2021 Free Software Foundation, Inc.
+   Copyright (C) 1993-2022 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Paul Eggert <eggert@twinsun.com>.
 
@@ -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;
     }