NetBSD/lib/libntp/calleapwhen.c

/*	$NetBSD: calleapwhen.c,v 1.4 1999/07/03 12:30:29 simonb Exp $	*/

/*
 * calleapwhen - determine the number of seconds to the next possible
 *		 leap occurance and the last one.
 */
#include <sys/types.h>

#include "ntp_types.h"
#include "ntp_calendar.h"
#include "ntp_stdlib.h"

/*
 * calleaptab - leaps occur at the end of December and June
 */
long calleaptab[10] = {
	-(JAN+FEBLEAP)*SECSPERDAY,	/* leap previous to cycle */
	(MAR+APR+MAY+JUN)*SECSPERDAY,	/* end of June */
	(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC)*SECSPERDAY, /* end of Dec */
	(MAR+APR+MAY+JUN)*SECSPERDAY + SECSPERYEAR,
	(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC)*SECSPERDAY + SECSPERYEAR,
	(MAR+APR+MAY+JUN)*SECSPERDAY + 2*SECSPERYEAR,
	(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC)*SECSPERDAY + 2*SECSPERYEAR,
	(MAR+APR+MAY+JUN)*SECSPERDAY + 3*SECSPERYEAR,
	(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC)*SECSPERDAY + 3*SECSPERYEAR,
	(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC+JAN+FEBLEAP+MAR+APR+MAY+JUN)
	    *SECSPERDAY + 3*SECSPERYEAR,	/* next after current cycle */
};

void
calleapwhen(ntpdate, leaplast, leapnext)
	u_long ntpdate;
	u_long *leaplast;
	u_long *leapnext;
{
	register u_long dateincycle;
	register int i;

	/*
	 * Find the offset from the start of the cycle
	 */
	dateincycle = ntpdate;
	if (dateincycle >= MAR1988)
		dateincycle -= MAR1988;
	else
		dateincycle -= MAR1900;

	while (dateincycle >= SECSPERCYCLE)
		dateincycle -= SECSPERCYCLE;

	/*
	 * Find where we are with respect to the leap events.
	 */
	for (i = 1; i < 9; i++)
		if (dateincycle < (u_long)calleaptab[i])
			break;
	
	/*
	 * i points at the next leap.  Compute the last and the next.
	 */
	*leaplast = (u_long)((long)dateincycle - calleaptab[i-1]);
	*leapnext = (u_long)(calleaptab[i] - (long)dateincycle);
}