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/*
* 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;
}
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