Merged in better support of ISO 8601 from elsie.nci.nih.gov.

Added the conversion specifiers %g and %G, that are replaced
by the year which contains the greater part of the week in question.

2 files changed, 118 insertions, 62 deletions

diff --git a/lib/libc/stdtime/strftime.3 b/lib/libc/stdtime/strftime.3
index 7ce1b2475295..fe916a17eb85 100644
--- a/lib/libc/stdtime/strftime.3
+++ b/lib/libc/stdtime/strftime.3
@@ -35,7 +35,7 @@
 .\"
 .\"     @(#)strftime.3	8.1 (Berkeley) 6/4/93
 .\"
-.Dd June 4, 1993
+.Dd October 4, 1997
 .Dt STRFTIME 3
 .Os
 .Sh NAME
@@ -113,6 +113,14 @@ representations.
 .It Cm %e
 is replaced by the day of month as a decimal number (1-31); single
 digits are preceded by a blank.
+.It Cm \&%G
+is replaced by a year as a decimal number with century.
+This year is the one that contains the greater part of
+the week (Monday as the first day of the week).
+.It Cm %g
+is replaced by the same year as in
+.Dq Li %G ,
+but as a decimal number without century (00-99).
 .It Cm \&%H
 is replaced by the hour (24-hour clock) as a decimal number (00-23).
 .It Cm %h
@@ -164,9 +172,10 @@ the week) as a decimal number (00-53).
 is replaced by the weekday (Monday as the first day of the week)
 as a decimal number (1-7).
 .It Cm \&%V
-is replaced by the week number of the year (the first
-Monday as the first day of week 1) as a
-decimal number (01-53).
+is replaced by the week number of the year (Monday as the first day of
+the week) as a decimal number (01-53).  If the week containing January
+1 has four or more days in the new year, then it is week 1; otherwise
+it is the last week of the previous year, and the next week is week 1.
 .It Cm %v
 is equivalent to
 .Dq Li %e-%b-%Y .
@@ -205,9 +214,34 @@ The
 .Fn strftime
 function
 conforms to
-.St -ansiC .
-The
-.Ql %s
-conversion specification is an extension.
+.St -ansiC
+with a lot of extensions including
+.Ql %C ,
+.Ql %D ,
+.Ql %E* ,
+.Ql %e ,
+.Ql %G ,
+.Ql %g ,
+.Ql %h ,
+.Ql %k ,
+.Ql %l ,
+.Ql %n ,
+.Ql %O* ,
+.Ql \&%R ,
+.Ql %r ,
+.Ql %s ,
+.Ql \&%T ,
+.Ql %t ,
+.Ql %u ,
+.Ql \&%V ,
+.Ql %+ .
+
+The peculiar week number and year occuring in the replacements of
+.Ql %G ,
+.Ql %g
+and
+.Ql \&%V
+are defined in ISO 8601: 1988.
+
 .Sh BUGS
 There is no conversion specification for the phase of the moon.
diff --git a/lib/libc/stdtime/strftime.c b/lib/libc/stdtime/strftime.c
index 126da8518167..893b784aaa23 100644
--- a/lib/libc/stdtime/strftime.c
+++ b/lib/libc/stdtime/strftime.c
@@ -17,7 +17,7 @@
 
 #ifdef LIBC_RCS
 static const char rcsid[] =
-	"$Id: strftime.c,v 1.17 1997/02/22 15:03:19 peter Exp $";
+	"$Id: strftime.c,v 1.18 1997/08/09 15:43:53 joerg Exp $";
 #endif
 
 #ifndef lint
@@ -234,67 +234,89 @@ label:
 				pt = _conv((t->tm_wday == 0) ? 7 : t->tm_wday,
 					"%d", pt, ptlim);
 				continue;
-			case 'V':
-				/*
-				** From Arnold Robbins' strftime version 3.0:
-				** "the week number of the year (the first
-				** Monday as the first day of week 1) as a
-				** decimal number (01-53).  The method for
-				** determining the week number is as specified
-				** by ISO 8601 (to wit: if the week containing
-				** January 1 has four or more days in the new
-				** year, then it is week 1, otherwise it is
-				** week 53 of the previous year and the next
-				** week is week 1)."
-				** (ado, 5/24/93)
-				*/
-				/*
-				** XXX--If January 1 falls on a Friday,
-				** January 1-3 are part of week 53 of the
-				** previous year.  By analogy, if January
-				** 1 falls on a Thursday, are December 29-31
-				** of the PREVIOUS year part of week 1???
-				** (ado 5/24/93)
-				*/
-				/*
-				** You are understood not to expect this.
-				*/
+			case 'V':	/* ISO 8601 week number */
+			case 'G':	/* ISO 8601 year (four digits) */
+			case 'g':	/* ISO 8601 year (two digits) */
+/*
+** From Arnold Robbins' strftime version 3.0:  "the week number of the
+** year (the first Monday as the first day of week 1) as a decimal number
+** (01-53)."
+** (ado, 1993-05-24)
+**
+** From "http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html" by Markus Kuhn:
+** "Week 01 of a year is per definition the first week which has the
+** Thursday in this year, which is equivalent to the week which contains
+** the fourth day of January. In other words, the first week of a new year
+** is the week which has the majority of its days in the new year. Week 01
+** might also contain days from the previous year and the week before week
+** 01 of a year is the last week (52 or 53) of the previous year even if
+** it contains days from the new year. A week starts with Monday (day 1)
+** and ends with Sunday (day 7).  For example, the first week of the year
+** 1997 lasts from 1996-12-30 to 1997-01-05..."
+** (ado, 1996-01-02)
+*/
 				{
-					int	i;
+					int	year;
+					int	yday;
+					int	wday;
+					int	w;
 
-					i = (t->tm_yday + 10 - (t->tm_wday ?
-						(t->tm_wday - 1) : 6)) / 7;
-					if (i == 0) {
+					year = t->tm_year + TM_YEAR_BASE;
+					yday = t->tm_yday;
+					wday = t->tm_wday;
+					for ( ; ; ) {
+						int	len;
+						int	bot;
+						int	top;
+
+						len = isleap(year) ?
+							DAYSPERLYEAR :
+							DAYSPERNYEAR;
 						/*
-						** What day of the week does
-						** January 1 fall on?
+						** What yday (-3 ... 3) does
+						** the ISO year begin on?
 						*/
-						i = t->tm_wday -
-							(t->tm_yday - 1);
+						bot = ((yday + 11 - wday) %
+							DAYSPERWEEK) - 3;
 						/*
-						** Fri Jan 1: 53
-						** Sun Jan 1: 52
-						** Sat Jan 1: 53 if previous
-						**		 year a leap
-						**		 year, else 52
+						** What yday does the NEXT
+						** ISO year begin on?
 						*/
-						if (i == TM_FRIDAY)
-							i = 53;
-						else if (i == TM_SUNDAY)
-							i = 52;
-						else	i = isleap(t->tm_year +
-								TM_YEAR_BASE) ?
-								53 : 52;
+						top = bot -
+							(len % DAYSPERWEEK);
+						if (top < -3)
+							top += DAYSPERWEEK;
+						top += len;
+						if (yday >= top) {
+							++year;
+							w = 1;
+							break;
+						}
+						if (yday >= bot) {
+							w = 1 + ((yday - bot) /
+								DAYSPERWEEK);
+							break;
+						}
+						--year;
+						yday += isleap(year) ?
+							DAYSPERLYEAR :
+							DAYSPERNYEAR;
+					}
 #ifdef XPG4_1994_04_09
-						/*
-						** As of 4/9/94, though,
-						** XPG4 calls for 53
-						** unconditionally.
-						*/
-						i = 53;
+					if ((w == 52
+					     && t->tm_mon == TM_JANUARY)
+					    || (w == 1
+						&& t->tm_mon == TM_DECEMBER))
+						w = 53;
 #endif /* defined XPG4_1994_04_09 */
-					}
-					pt = _conv(i, "%02d", pt, ptlim);
+					if (*format == 'V')
+						pt = _conv(w, "%02d",
+							pt, ptlim);
+					else if (*format == 'g') {
+						pt = _conv(year % 100, "%02d",
+							pt, ptlim);
+					} else	pt = _conv(year, "%04d",
+							pt, ptlim);
 				}
 				continue;
 			case 'v':