59 lines
1.7 KiB
C
59 lines
1.7 KiB
C
#include <time.h>
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#include "timeutil.h"
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/* TODO: mktime: DST not supported */
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time_t mktime(struct tm *time)
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{
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/* Normalize time */
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time->tm_min += (time->tm_sec / 60);
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time->tm_hour += (time->tm_min / 60);
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time->tm_mday += (time->tm_hour / 24);
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time->tm_sec %= 60;
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time->tm_min %= 60;
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time->tm_hour %= 24;
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/* Normalize date */
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int days = daysin(time->tm_mon, time->tm_year + 1900);
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while(time->tm_mday > days) {
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time->tm_mday -= days;
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if(++time->tm_mon == 12) {
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time->tm_mon = 0;
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time->tm_year++;
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}
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days = daysin(time->tm_mon, time->tm_year + 1900);
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}
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/* Determine day in year */
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time->tm_yday = time->tm_mday - 1;
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for(int i = 0; i < time->tm_mon; i++)
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time->tm_yday += daysin(i, time->tm_year + 1900);
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/* Determine day in week. The calendar has a period of 400 years and
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1601-01-01 was a Monday. */
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/* Years elapsed since last 400n+1 year (1601-2001-etc). */
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int yr = (time->tm_year + 1900 - 1) % 400;
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/* Leap years during this period */
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int leaps = (yr / 4) - (yr >= 100) - (yr >= 200) - (yr >= 300);
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/* Days elapsed since 01-01 on the last 400n+1 year */
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days = 365 * yr + leaps + time->tm_yday;
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/* Current day of week (1 is Monday on 01-01 of last 400n+1 year) */
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time->tm_wday = (1 + days) % 7;
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/* We don't determine DST at the targeted time */
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time->tm_isdst = 0;
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/* Number of periods elapsed since 1601-01-01 (may be negative) */
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int periods = (time->tm_year + 1900 - 1601) / 400;
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periods -= (time->tm_year + 1900 < 1601);
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/* Days elapsed since 1970-01-01; the calendar period is 146097 days
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and there are 134774 days between 1601-01-01 and 1970-01-01 */
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days += 146097 * periods - 134774;
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time_t t = days;
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t = 24 * t + time->tm_hour;
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t = 60 * t + time->tm_min;
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t = 60 * t + time->tm_sec;
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return t;
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}
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