gistfile1.h

/* timestamp_pl_interval()
 * Add a interval to a timestamp data type.
 * Note that interval has provisions for qualitative year/month and day
 *	units, so try to do the right thing with them.
 * To add a month, increment the month, and use the same day of month.
 * Then, if the next month has fewer days, set the day of month
 *	to the last day of month.
 * To add a day, increment the mday, and use the same time of day.
 * Lastly, add in the "quantitative time".
 */
Datum
timestamp_pl_interval(PG_FUNCTION_ARGS)
{
	Timestamp	timestamp = PG_GETARG_TIMESTAMP(0);
	Interval   *span = PG_GETARG_INTERVAL_P(1);
	Timestamp	result;

	if (TIMESTAMP_NOT_FINITE(timestamp))
		result = timestamp;
	else
	{
		if (span->month != 0)
		{
			struct pg_tm tt,
					   *tm = &tt;
			fsec_t		fsec;

			if (timestamp2tm(timestamp, NULL, tm, &fsec, NULL, NULL) != 0)
				ereport(ERROR,
						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
						 errmsg("timestamp out of range")));

			tm->tm_mon += span->month;
			if (tm->tm_mon > MONTHS_PER_YEAR)
			{
				tm->tm_year += (tm->tm_mon - 1) / MONTHS_PER_YEAR;
				tm->tm_mon = ((tm->tm_mon - 1) % MONTHS_PER_YEAR) + 1;
			}
			else if (tm->tm_mon < 1)
			{
				tm->tm_year += tm->tm_mon / MONTHS_PER_YEAR - 1;
				tm->tm_mon = tm->tm_mon % MONTHS_PER_YEAR + MONTHS_PER_YEAR;
			}

			/* adjust for end of month boundary problems... */
			if (tm->tm_mday > day_tab[isleap(tm->tm_year)][tm->tm_mon - 1])
				tm->tm_mday = (day_tab[isleap(tm->tm_year)][tm->tm_mon - 1]);

			if (tm2timestamp(tm, fsec, NULL, &timestamp) != 0)
				ereport(ERROR,
						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
						 errmsg("timestamp out of range")));
		}

		if (span->day != 0)
		{
			struct pg_tm tt,
					   *tm = &tt;
			fsec_t		fsec;
			int			julian;

			if (timestamp2tm(timestamp, NULL, tm, &fsec, NULL, NULL) != 0)
				ereport(ERROR,
						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
						 errmsg("timestamp out of range")));

			/* Add days by converting to and from julian */
			julian = date2j(tm->tm_year, tm->tm_mon, tm->tm_mday) + span->day;
			j2date(julian, &tm->tm_year, &tm->tm_mon, &tm->tm_mday);

			if (tm2timestamp(tm, fsec, NULL, &timestamp) != 0)
				ereport(ERROR,
						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
						 errmsg("timestamp out of range")));
		}

		timestamp += span->time;
		result = timestamp;
	}

	PG_RETURN_TIMESTAMP(result);
}