1 files changed, 62 insertions, 0 deletions
diff --git a/usr.sbin/xntpd/lib/calyearstart.c b/usr.sbin/xntpd/lib/calyearstart.c
new file mode 100644
index 0000000..1bb3321
--- /dev/null
+++ b/usr.sbin/xntpd/lib/calyearstart.c
@@ -0,0 +1,62 @@
+/* calyearstart.c,v 3.1 1993/07/06 01:08:06 jbj Exp
+ * calyearstart - determine the NTP time at midnight of January 1 in
+ *		  the year of the given date.
+ */
+#include <sys/types.h>
+
+#include "ntp_types.h"
+#include "ntp_calendar.h"
+#include "ntp_stdlib.h"
+
+/*
+ * calyeartab - year start offsets from the beginning of a cycle
+ */
+U_LONG calyeartab[YEARSPERCYCLE] = {
+	(SECSPERLEAPYEAR-JANFEBLEAP),
+	(SECSPERLEAPYEAR-JANFEBLEAP) + SECSPERYEAR,
+	(SECSPERLEAPYEAR-JANFEBLEAP) + 2*SECSPERYEAR,
+	(SECSPERLEAPYEAR-JANFEBLEAP) + 3*SECSPERYEAR
+};
+
+U_LONG
+calyearstart(dateinyear)
+	register U_LONG dateinyear;
+{
+	register U_LONG cyclestart;
+	register U_LONG nextyear, lastyear;
+	register int i;
+
+	/*
+	 * Find the start of the cycle this is in.
+	 */
+	if (dateinyear >= MAR1988)
+		cyclestart = MAR1988;
+	else
+		cyclestart = MAR1900;
+	while ((cyclestart + SECSPERCYCLE) <= dateinyear)
+		cyclestart += SECSPERCYCLE;
+	
+	/*
+	 * If we're in the first year of the cycle, January 1 is
+	 * two months back from the cyclestart and the year is
+	 * a leap year.
+	 */
+	lastyear = cyclestart + calyeartab[0];
+	if (dateinyear < lastyear)
+		return (cyclestart - JANFEBLEAP);
+
+	/*
+	 * Look for an intermediate year
+	 */
+	for (i = 1; i < YEARSPERCYCLE; i++) {
+		nextyear = cyclestart + calyeartab[i];
+		if (dateinyear < nextyear)
+			return lastyear;
+		lastyear = nextyear;
+	}
+
+	/*
+	 * Not found, must be in last two months of cycle
+	 */
+	return nextyear;
+}