53 lines
1.3 KiB
C
53 lines
1.3 KiB
C
#include <time.h>
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#define YEARSIZE(year) ((year) % 4 ? 365 : 366)
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#define FIRSTSUNDAY(t) (((t)->tm_yday - (t)->tm_wday + 420) % 7)
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#define SUNDAY(day, t) ((day) < 58 ? \
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((day) < FIRSTSUNDAY(t) ? FIRSTSUNDAY(t) :
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static int
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last_sunday(d, t)
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register int d;
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register struct tm *t;
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{
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int first = FIRSTSUNDAY(t);
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if (d >= 58 && YEARSIZE(t->tm_year)) d++;
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if (d < first) return first;
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return d - (d - first) % 7;
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}
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struct tm *
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localtime(clock)
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long *clock;
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{
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register struct tm *gmt;
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long cl;
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int begindst, enddst;
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extern int daylight;
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extern long timezone;
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tzset();
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cl = *clock - timezone;
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gmt = gmtime(&cl);
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if (daylight) {
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/* daylight saving time.
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Unfortunately, rules differ for different countries.
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Implemented here are heuristics that got it right
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in Holland, over the last couple of years.
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Of course, there is no algorithm. It is all
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politics ...
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*/
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begindst = last_sunday(89, gmt); /* last Sun before Apr */
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enddst = last_sunday(272, gmt); /* last Sun in Sep */
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if ((gmt->tm_yday>begindst ||
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(gmt->tm_yday==begindst && gmt->tm_hour>=2)) &&
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(gmt->tm_yday<enddst ||
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(gmt->tm_yday==enddst && gmt->tm_hour<3))) {
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cl += 1*60*60;
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gmt = gmtime(&cl);
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gmt->tm_isdst++;
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}
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}
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return gmt;
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}
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