63 lines
1.3 KiB
C
63 lines
1.3 KiB
C
/*
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* calyearstart - determine the NTP time at midnight of January 1 in
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* the year of the given date.
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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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* calyeartab - year start offsets from the beginning of a cycle
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*/
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u_long calyeartab[YEARSPERCYCLE] = {
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(SECSPERLEAPYEAR-JANFEBLEAP),
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(SECSPERLEAPYEAR-JANFEBLEAP) + SECSPERYEAR,
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(SECSPERLEAPYEAR-JANFEBLEAP) + 2*SECSPERYEAR,
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(SECSPERLEAPYEAR-JANFEBLEAP) + 3*SECSPERYEAR
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};
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u_long
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calyearstart(dateinyear)
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register u_long dateinyear;
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{
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register u_long cyclestart;
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register u_long nextyear, lastyear;
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register int i;
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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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if (dateinyear >= MAR1988)
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cyclestart = MAR1988;
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else
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cyclestart = MAR1900;
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while ((cyclestart + SECSPERCYCLE) <= dateinyear)
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cyclestart += SECSPERCYCLE;
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/*
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* If we're in the first year of the cycle, January 1 is
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* two months back from the cyclestart and the year is
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* a leap year.
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*/
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lastyear = cyclestart + calyeartab[0];
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if (dateinyear < lastyear)
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return (cyclestart - JANFEBLEAP);
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/*
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* Look for an intermediate year
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*/
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for (i = 1; i < YEARSPERCYCLE; i++) {
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nextyear = cyclestart + calyeartab[i];
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if (dateinyear < nextyear)
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return lastyear;
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lastyear = nextyear;
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}
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/*
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* Not found, must be in last two months of cycle
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*/
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return nextyear;
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}
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