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-rw-r--r--time/mktime.c45
1 files changed, 23 insertions, 22 deletions
diff --git a/time/mktime.c b/time/mktime.c
index 2908db0784..673bb48266 100644
--- a/time/mktime.c
+++ b/time/mktime.c
@@ -350,31 +350,32 @@ __mktime_internal (tp, convert, offset)
/* If we have a match, check whether tm.tm_isdst has the requested
value, if any. */
- if (dt == 0 && 0 <= isdst && 0 <= tm.tm_isdst)
+ if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
{
- int dst_diff = (isdst != 0) - (tm.tm_isdst != 0);
- if (dst_diff)
+ /* tm.tm_isdst has the wrong value. Look for a neighboring
+ time with the right value, and use its UTC offset.
+ Heuristic: probe the previous three calendar quarters (approximately),
+ looking for the desired isdst. This isn't perfect,
+ but it's good enough in practice. */
+ int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
+ int i;
+
+ /* If we're too close to the time_t limit, look in future quarters. */
+ if (t < TIME_T_MIN + 3 * quarter)
+ quarter = -quarter;
+
+ for (i = 1; i <= 3; i++)
{
- /* Move two hours in the direction indicated by the disagreement,
- probe some more, and switch to a new time if found.
- The largest known fallback due to daylight savings is two hours:
- once, in Newfoundland, 1988-10-30 02:00 -> 00:00. */
- time_t ot = t - 2 * 60 * 60 * dst_diff;
- while (--remaining_probes != 0)
+ time_t ot = t - i * quarter;
+ struct tm otm;
+ ranged_convert (convert, &ot, &otm);
+ if (otm.tm_isdst == isdst)
{
- struct tm otm;
- dt = ydhms_tm_diff (year, yday, hour, min, sec,
- ranged_convert (convert, &ot, &otm));
- if (dt == 0
- || (ot + dt == t
- && dst_diff == (isdst != 0) - (tm.tm_isdst != 0)))
- {
- t = ot;
- tm = otm;
- break;
- }
- if ((ot += dt) == t)
- break; /* Avoid a redundant probe. */
+ /* We found the desired tm_isdst.
+ Extrapolate back to the desired time. */
+ t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
+ ranged_convert (convert, &t, &tm);
+ break;
}
}
}