63 lines
1.4 KiB
C
63 lines
1.4 KiB
C
/* 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;
|
|
}
|