132 lines
3.1 KiB
C
132 lines
3.1 KiB
C
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/* clocktime.c,v 3.1 1993/07/06 01:08:07 jbj Exp
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* clocktime - compute the NTP date from a day of year, hour, minute
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* and second.
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*/
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#include "ntp_fp.h"
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#include "ntp_unixtime.h"
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#include "ntp_stdlib.h"
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/*
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* Hacks to avoid excercising the multiplier. I have no pride.
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*/
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#define MULBY10(x) (((x)<<3) + ((x)<<1))
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#define MULBY60(x) (((x)<<6) - ((x)<<2)) /* watch overflow */
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#define MULBY24(x) (((x)<<4) + ((x)<<3))
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/*
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* Two days, in seconds.
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*/
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#define TWODAYS (2*24*60*60)
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/*
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* We demand that the time be within CLOSETIME seconds of the receive
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* time stamp. This is about 4 hours, which hopefully should be
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* wide enough to collect most data, while close enough to keep things
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* from getting confused.
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*/
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#define CLOSETIME (4*60*60)
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int
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clocktime(yday, hour, minute, second, tzoff, rec_ui, yearstart, ts_ui)
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int yday;
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int hour;
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int minute;
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int second;
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int tzoff;
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U_LONG rec_ui;
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U_LONG *yearstart;
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U_LONG *ts_ui;
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{
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register LONG tmp;
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register U_LONG date;
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register U_LONG yst;
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/*
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* Compute the offset into the year in seconds. Note that
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* this could come out to be a negative number.
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*/
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tmp = (LONG)(MULBY24((yday-1)) + hour + tzoff);
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tmp = MULBY60(tmp) + (LONG)minute;
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tmp = MULBY60(tmp) + (LONG)second;
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/*
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* Initialize yearstart, if necessary.
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*/
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yst = *yearstart;
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if (yst == 0) {
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yst = calyearstart(rec_ui);
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*yearstart = yst;
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}
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/*
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* Now the fun begins. We demand that the received clock time
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* be within CLOSETIME of the receive timestamp, but
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* there is uncertainty about the year the timestamp is in.
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* Use the current year start for the first check, this should
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* work most of the time.
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*/
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date = (U_LONG)(tmp + (LONG)yst);
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if (date < (rec_ui + CLOSETIME) &&
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date > (rec_ui - CLOSETIME)) {
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*ts_ui = date;
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return 1;
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}
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/*
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* Trouble. Next check is to see if the year rolled over and, if
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* so, try again with the new year's start.
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*/
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yst = calyearstart(rec_ui);
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if (yst != *yearstart) {
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date = (U_LONG)((LONG)yst + tmp);
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*ts_ui = date;
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if (date < (rec_ui + CLOSETIME) &&
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date > (rec_ui - CLOSETIME)) {
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*yearstart = yst;
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return 1;
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}
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}
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/*
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* Here we know the year start matches the current system
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* time. One remaining possibility is that the time code
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* is in the year previous to that of the system time. This
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* is only worth checking if the receive timestamp is less
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* than a couple of days into the new year.
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*/
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if ((rec_ui - yst) < TWODAYS) {
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yst = calyearstart(yst - TWODAYS);
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if (yst != *yearstart) {
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date = (U_LONG)(tmp + (LONG)yst);
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if (date < (rec_ui + CLOSETIME) &&
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date > (rec_ui - CLOSETIME)) {
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*yearstart = yst;
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*ts_ui = date;
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return 1;
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}
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}
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}
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/*
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* One last possibility is that the time stamp is in the year
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* following the year the system is in. Try this one before
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* giving up.
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*/
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yst = calyearstart(rec_ui + TWODAYS);
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if (yst != *yearstart) {
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date = (U_LONG)((LONG)yst + tmp);
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if (date < (rec_ui + CLOSETIME) &&
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date > (rec_ui - CLOSETIME)) {
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*yearstart = yst;
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*ts_ui = date;
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return 1;
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}
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}
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/*
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* Give it up.
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*/
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return 0;
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}
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