This patch fixes some problems in date handling for atypical dates.

Here is a summary:
Be more careful to check input string lengths as well as values
 when deciding whether a field is a year field.  Assume *anything* longer
 than 2 digits (if it isn't a special-case doy) is a valid year.
 This should fix the "Y1K" and "Y10K" problems
  pointed out by Massimo recently.
Check usage of BC to require a positive-valued year; before just used it
 to flip the sign of the year without checking. This led to problems
 near year zero.
Allow a 5 digit "concatenated date" of 2 digit year plus day of year.
Do 2->4 digit year correction for 6 and 5 digit "concatenated dates".
 Somehow forgot this originally. Guess not many folks use it...
Move common macros to dt.h.

Author: Thomas G. Lockhart

src/backend/utils/adt/datetime.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/datetime.c,v 1.25.2.1 1998/12/31 16:34:47 thomas Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/datetime.c,v 1.25.2.2 1999/02/13 05:59:34 thomas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -27,12 +27,13 @@
 
 static int	date2tm(DateADT dateVal, int *tzp, struct tm * tm, double *fsec, char **tzn);
 
-
+#if 0
 static int	day_tab[2][12] = {
 	{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
 {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}};
 
 #define isleap(y) (((y % 4) == 0 && (y % 100) != 0) || (y % 400) == 0)
+#endif
 
 #define UTIME_MINYEAR (1901)
 #define UTIME_MINMONTH (12)
@@ -99,10 +100,12 @@ date_in(char *str)
 			elog(ERROR, "Unrecognized date external representation %s", str);
 	}
 
+#if 0
 	if (tm->tm_year < 0 || tm->tm_year > 32767)
 		elog(ERROR, "date_in: year must be limited to values 0 through 32767 in '%s'", str);
 	if (tm->tm_mon < 1 || tm->tm_mon > 12)
 		elog(ERROR, "date_in: month must be limited to values 1 through 12 in '%s'", str);
+#endif
 	if (tm->tm_mday < 1 || tm->tm_mday > day_tab[isleap(tm->tm_year)][tm->tm_mon - 1])
 		elog(ERROR, "date_in: day must be limited to values 1 through %d in '%s'",
 			 day_tab[isleap(tm->tm_year)][tm->tm_mon - 1], str);