106 lines
2.4 KiB
C
106 lines
2.4 KiB
C
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/* caljulian.c,v 3.1 1993/07/06 01:08:00 jbj Exp
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* caljulian - determine the Julian date from an NTP time.
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*/
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#include <sys/types.h>
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#include "ntp_types.h"
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#include "ntp_calendar.h"
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#include "ntp_stdlib.h"
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/*
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* calmonthtab - month start offsets from the beginning of a cycle.
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*/
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static u_short calmonthtab[12] = {
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0, /* March */
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MAR, /* April */
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(MAR+APR), /* May */
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(MAR+APR+MAY), /* June */
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(MAR+APR+MAY+JUN), /* July */
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(MAR+APR+MAY+JUN+JUL), /* August */
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(MAR+APR+MAY+JUN+JUL+AUG), /* September */
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(MAR+APR+MAY+JUN+JUL+AUG+SEP), /* October */
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(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT), /* November */
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(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV), /* December */
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(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC), /* January */
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(MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC+JAN), /* February */
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};
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/*
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* caldaytab - calendar year start day offsets
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*/
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static u_short caldaytab[YEARSPERCYCLE] = {
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(DAYSPERYEAR - (JAN + FEB)),
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((DAYSPERYEAR * 2) - (JAN + FEB)),
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((DAYSPERYEAR * 3) - (JAN + FEB)),
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((DAYSPERYEAR * 4) - (JAN + FEB)),
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};
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void
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caljulian(ntptime, jt)
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U_LONG ntptime;
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register struct calendar *jt;
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{
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register int i;
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register U_LONG nt;
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register u_short snt;
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register int cyear;
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/*
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* Find the start of the cycle this is in.
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*/
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nt = ntptime;
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if (nt >= MAR1988) {
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cyear = CYCLE22;
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nt -= MAR1988;
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} else {
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cyear = 0;
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nt -= MAR1900;
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}
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while (nt >= SECSPERCYCLE) {
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nt -= SECSPERCYCLE;
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cyear++;
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}
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/*
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* Seconds, minutes and hours are too hard to do without
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* divides, so we don't.
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*/
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jt->second = nt % SECSPERMIN;
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nt /= SECSPERMIN; /* nt in minutes */
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jt->minute = nt % MINSPERHR;
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snt = nt / MINSPERHR; /* snt in hours */
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jt->hour = snt % HRSPERDAY;
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snt /= HRSPERDAY; /* nt in days */
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/*
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* snt is now the number of days into the cycle, from 0 to 1460.
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*/
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cyear <<= 2;
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if (snt < caldaytab[0]) {
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jt->yearday = snt + JAN + FEBLEAP + 1; /* first year is leap */
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} else {
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for (i = 1; i < YEARSPERCYCLE; i++)
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if (snt < caldaytab[i])
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break;
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jt->yearday = snt - caldaytab[i-1] + 1;
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cyear += i;
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}
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jt->year = cyear + 1900;
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/*
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* One last task, to compute the month and day. Normalize snt to
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* a day within a cycle year.
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*/
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while (snt >= DAYSPERYEAR)
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snt -= DAYSPERYEAR;
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for (i = 0; i < 11; i++)
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if (snt < calmonthtab[i+1])
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break;
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if (i > 9)
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jt->month = i - 9; /* January or February */
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else
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jt->month = i + 3; /* March through December */
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jt->monthday = snt - calmonthtab[i] + 1;
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}
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