118 lines
2.4 KiB
C
118 lines
2.4 KiB
C
/* $NetBSD: caljulian.c,v 1.1.1.1 2000/03/29 12:38:49 simonb Exp $ */
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/*
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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 - days-in-the-month table
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*/
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static u_short calmonthtab[11] = {
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JAN,
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FEB,
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MAR,
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APR,
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MAY,
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JUN,
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JUL,
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AUG,
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SEP,
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OCT,
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NOV
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};
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void
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caljulian(
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u_long ntptime,
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register struct calendar *jt
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)
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{
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u_long ntp_day;
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u_long minutes;
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/*
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* Absolute, zero-adjusted Christian era day, starting from the
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* mythical day 12/1/1 BC
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*/
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u_long acez_day;
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u_long d400; /* Days into a Gregorian cycle */
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u_long d100; /* Days into a normal century */
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u_long d4; /* Days into a 4-year cycle */
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u_long n400; /* # of Gregorian cycles */
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u_long n100; /* # of normal centuries */
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u_long n4; /* # of 4-year cycles */
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u_long n1; /* # of years into a leap year */
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/* cycle */
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/*
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* Do the easy stuff first: take care of hh:mm:ss, ignoring leap
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* seconds
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*/
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jt->second = (u_char)(ntptime % SECSPERMIN);
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minutes = ntptime / SECSPERMIN;
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jt->minute = (u_char)(minutes % MINSPERHR);
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jt->hour = (u_char)((minutes / MINSPERHR) % HRSPERDAY);
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/*
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* Find the day past 1900/01/01 00:00 UTC
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*/
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ntp_day = ntptime / SECSPERDAY;
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acez_day = DAY_NTP_STARTS + ntp_day - 1;
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n400 = acez_day/GREGORIAN_CYCLE_DAYS;
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d400 = acez_day%GREGORIAN_CYCLE_DAYS;
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n100 = d400 / GREGORIAN_NORMAL_CENTURY_DAYS;
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d100 = d400 % GREGORIAN_NORMAL_CENTURY_DAYS;
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n4 = d100 / GREGORIAN_NORMAL_LEAP_CYCLE_DAYS;
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d4 = d100 % GREGORIAN_NORMAL_LEAP_CYCLE_DAYS;
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n1 = d4 / DAYSPERYEAR;
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/*
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* Calculate the year and year-of-day
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*/
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jt->yearday = (u_short)(1 + d4%DAYSPERYEAR);
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jt->year = (u_short)(400*n400 + 100*n100 + n4*4 + n1);
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if (n100 == 4 || n1 == 4)
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{
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/*
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* If the cycle year ever comes out to 4, it must be December 31st
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* of a leap year.
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*/
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jt->month = 12;
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jt->monthday = 31;
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jt->yearday = 366;
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}
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else
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{
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/*
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* Else, search forwards through the months to get the right month
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* and date.
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*/
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int monthday;
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jt->year++;
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monthday = jt->yearday;
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for (jt->month=0;jt->month<11; jt->month++)
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{
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int t;
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t = monthday - calmonthtab[jt->month];
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if (jt->month == 1 && is_leapyear(jt->year))
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t--;
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if (t > 0)
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monthday = t;
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else
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break;
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}
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jt->month++;
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jt->monthday = monthday;
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}
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}
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