*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/datetime.c,v 1.116 2003/08/27 23:29:28 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/datetime.c,v 1.117 2003/09/13 21:12:38 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* (ie, regular or daylight-savings time) at that time. Set the struct tm's
* tm_isdst field accordingly, and return the actual timezone offset.
*
- * This subroutine exists to centralize uses of mktime() and defend against
- * mktime() bugs/restrictions on various platforms. This should be
- * the *only* call of mktime() in the backend.
+ * Note: this subroutine exists because mktime() has such a spectacular
+ * variety of, ahem, odd behaviors on various platforms. We used to try to
+ * use mktime() here, but finally gave it up as a bad job. Avoid using
+ * mktime() anywhere else.
*/
int
DetermineLocalTimeZone(struct tm * tm)
}
else if (IS_VALID_UTIME(tm->tm_year, tm->tm_mon, tm->tm_mday))
{
-#if defined(HAVE_TM_ZONE) || defined(HAVE_INT_TIMEZONE)
+ /*
+ * First, generate the time_t value corresponding to the given
+ * y/m/d/h/m/s taken as GMT time. This will not overflow (at
+ * least not for time_t taken as signed) because of the range
+ * check we did above.
+ */
+ long day,
+ mysec,
+ locsec,
+ delta1,
+ delta2;
+ time_t mytime;
+ struct tm *tx;
+
+ day = date2j(tm->tm_year, tm->tm_mon, tm->tm_mday) - UNIX_EPOCH_JDATE;
+ mysec = tm->tm_sec + (tm->tm_min + (day * 24 + tm->tm_hour) * 60) * 60;
+ mytime = (time_t) mysec;
/*
- * Some buggy mktime() implementations may change the
- * year/month/day when given a time right at a DST boundary. To
- * prevent corruption of the caller's data, give mktime() a
- * copy...
+ * Use localtime to convert that time_t to broken-down time,
+ * and reassemble to get a representation of local time.
*/
- struct tm tt,
- *tmp = &tt;
+ tx = localtime(&mytime);
+ day = date2j(tx->tm_year + 1900, tx->tm_mon + 1, tx->tm_mday) -
+ UNIX_EPOCH_JDATE;
+ locsec = tx->tm_sec + (tx->tm_min + (day * 24 + tx->tm_hour) * 60) * 60;
- *tmp = *tm;
- /* change to Unix conventions for year/month */
- tmp->tm_year -= 1900;
- tmp->tm_mon -= 1;
+ /*
+ * The local time offset corresponding to that GMT time is now
+ * computable as mysec - locsec.
+ */
+ delta1 = mysec - locsec;
- /* indicate timezone unknown */
- tmp->tm_isdst = -1;
+ /*
+ * However, if that GMT time and the local time we are
+ * actually interested in are on opposite sides of a
+ * daylight-savings-time transition, then this is not the time
+ * offset we want. So, adjust the time_t to be what we think
+ * the GMT time corresponding to our target local time is, and
+ * repeat the localtime() call and delta calculation.
+ */
+ mysec += delta1;
+ mytime = (time_t) mysec;
+ tx = localtime(&mytime);
+ day = date2j(tx->tm_year + 1900, tx->tm_mon + 1, tx->tm_mday) -
+ UNIX_EPOCH_JDATE;
+ locsec = tx->tm_sec + (tx->tm_min + (day * 24 + tx->tm_hour) * 60) * 60;
+ delta2 = mysec - locsec;
- if (mktime(tmp) != ((time_t) -1) &&
- tmp->tm_isdst >= 0)
- {
- /* mktime() succeeded, trust its result */
- tm->tm_isdst = tmp->tm_isdst;
-
-#if defined(HAVE_TM_ZONE)
- /* tm_gmtoff is Sun/DEC-ism */
- tz = -(tmp->tm_gmtoff);
-#elif defined(HAVE_INT_TIMEZONE)
- tz = ((tmp->tm_isdst > 0) ? (TIMEZONE_GLOBAL - 3600) : TIMEZONE_GLOBAL);
-#endif /* HAVE_INT_TIMEZONE */
- }
- else
+ /*
+ * We may have to do it again to get the correct delta.
+ *
+ * It might seem we should just loop until we get the same delta
+ * twice in a row, but if we've been given an "impossible" local
+ * time (in the gap during a spring-forward transition) we'd never
+ * get out of the loop. The behavior we want is that "impossible"
+ * times are taken as standard time, and also that ambiguous times
+ * (during a fall-back transition) are taken as standard time.
+ * Therefore, we bias the code to prefer the standard-time solution.
+ */
+ if (delta2 != delta1 && tx->tm_isdst != 0)
{
- /*
- * We have a buggy (not to say deliberately brain damaged)
- * mktime(). Work around it by using localtime() instead.
- *
- * First, generate the time_t value corresponding to the given
- * y/m/d/h/m/s taken as GMT time. This will not overflow (at
- * least not for time_t taken as signed) because of the range
- * check we did above.
- */
- long day,
- mysec,
- locsec,
- delta1,
- delta2;
- time_t mytime;
-
- day = date2j(tm->tm_year, tm->tm_mon, tm->tm_mday) - UNIX_EPOCH_JDATE;
- mysec = tm->tm_sec + (tm->tm_min + (day * 24 + tm->tm_hour) * 60) * 60;
+ mysec += (delta2 - delta1);
mytime = (time_t) mysec;
-
- /*
- * Use localtime to convert that time_t to broken-down time,
- * and reassemble to get a representation of local time.
- */
- tmp = localtime(&mytime);
- day = date2j(tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday) -
- UNIX_EPOCH_JDATE;
- locsec = tmp->tm_sec + (tmp->tm_min + (day * 24 + tmp->tm_hour) * 60) * 60;
-
- /*
- * The local time offset corresponding to that GMT time is now
- * computable as mysec - locsec.
- */
- delta1 = mysec - locsec;
-
- /*
- * However, if that GMT time and the local time we are
- * actually interested in are on opposite sides of a
- * daylight-savings-time transition, then this is not the time
- * offset we want. So, adjust the time_t to be what we think
- * the GMT time corresponding to our target local time is, and
- * repeat the localtime() call and delta calculation. We may
- * have to do it twice before we have a trustworthy delta.
- *
- * Note: think not to put a loop here, since if we've been given
- * an "impossible" local time (in the gap during a
- * spring-forward transition) we'd never get out of the loop.
- * Twice is enough to give the behavior we want, which is that
- * "impossible" times are taken as standard time, while at a
- * fall-back boundary ambiguous times are also taken as
- * standard.
- */
- mysec += delta1;
- mytime = (time_t) mysec;
- tmp = localtime(&mytime);
- day = date2j(tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday) -
+ tx = localtime(&mytime);
+ day = date2j(tx->tm_year + 1900, tx->tm_mon + 1, tx->tm_mday) -
UNIX_EPOCH_JDATE;
- locsec = tmp->tm_sec + (tmp->tm_min + (day * 24 + tmp->tm_hour) * 60) * 60;
+ locsec = tx->tm_sec + (tx->tm_min + (day * 24 + tx->tm_hour) * 60) * 60;
delta2 = mysec - locsec;
- if (delta2 != delta1)
- {
- mysec += (delta2 - delta1);
- mytime = (time_t) mysec;
- tmp = localtime(&mytime);
- day = date2j(tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday) -
- UNIX_EPOCH_JDATE;
- locsec = tmp->tm_sec + (tmp->tm_min + (day * 24 + tmp->tm_hour) * 60) * 60;
- delta2 = mysec - locsec;
- }
- tm->tm_isdst = tmp->tm_isdst;
- tz = (int) delta2;
}
-#else /* not (HAVE_TM_ZONE || HAVE_INT_TIMEZONE) */
- /* Assume UTC if no system timezone info available */
- tm->tm_isdst = 0;
- tz = 0;
-#endif
+ tm->tm_isdst = tx->tm_isdst;
+ tz = (int) delta2;
}
else
{
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