diff options
Diffstat (limited to 'time/mktime.c')
| -rw-r--r-- | time/mktime.c | 45 |
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; } } } |