Add isotime() and isodate() functions to libc.

sys/man/2/ctime

@@ -1,6 +1,6 @@
 .TH CTIME 2
 .SH NAME
-ctime, localtime, gmtime, asctime, tm2sec, timezone \- convert date and time
+ctime, localtime, gmtime, asctime, tm2sec, timezone, isodate, isotime \- convert date and time
 .SH SYNOPSIS
 .B #include <u.h>
 .br
@@ -23,6 +23,12 @@ char*	asctime(Tm *tm)
 long	tm2sec(Tm *tm)
 .PP
 .B
+char*	isodate(Tm *tm)
+.PP
+.B
+char*	isotime(Tm *tm)
+.PP
+.B
 /env/timezone
 .SH DESCRIPTION
 .I Ctime
@@ -84,6 +90,13 @@ if
 is not
 .BR GMT .
 .PP
+.I Isotime 
+converts a broken-down time to a date and timestamp according to ISO-8601 with timezone, and returns a string of up to 24 characters.
+.PP
+.I Isodate 
+converts a broken-down time to a datestamp 
+without timezone, and returns a 10 byte string.
+.PP
 When local time is first requested,
 the program consults the
 .B timezone

sys/src/libc/9sys/ctime.c

@@ -299,3 +299,50 @@ rd_long(char **f, long *p)
 	*p = l;
 	return 0;
 }
+
+char*
+isodate(Tm *t)
+{
+	static char c[10+14+1]; /* leave room to append isotime */
+
+	ct_numb(c, t->year / 100 + 119);
+	ct_numb(c+2, t->year % 100 + 100);
+	c[4] = '-';
+	ct_numb(c+5, t->mon + 101);
+	c[7] = '-';
+	ct_numb(c+8, t->mday + 100);
+	c[10] = 0;
+	return c;
+}
+
+char*
+isotime(Tm *t)
+{
+	int tz;
+	char *c, *d;
+	d = isodate(t);
+	c = d + 10; /* append to isodate */
+	c[0] = 'T';
+	ct_numb(c+1, t->hour+100);
+	c[3] = ':';
+	ct_numb(c+4, t->min+100);
+	c[6] = ':';
+	ct_numb(c+7, t->sec+100);
+	tz = t->tzoff / 60;
+	if(t->tzoff) {
+		/* localtime */
+		if (t->tzoff > 0) {
+			c[9] = '+';
+		} else {
+			c[9] = '-';
+			tz = -tz;
+		}
+		ct_numb(c+10, tz / 60 + 100);
+		ct_numb(c+12, tz % 60 + 100);
+		c[14] = 0;
+	} else {
+		c[9] = 'Z';
+		c[10] = 0;
+	}
+	return d;
+}