src/datetime_un.c


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#include "datetime.h"

/* roughly 100x faster than mktime() */

datetime_sec datetime_untai(struct datetime *dt)
{
  int year;
  int day;
  int mon;

  year = dt->year + 1900;

  mon = dt->mon;
  if (mon >= 2) {
    mon -= 2;
  } else {
    mon += 10;
    --year;
  }

  day = (dt->mday - 1) * 10 + 5 + 306 * mon;
  day /= 10;

  if (day == 365) {
    year -= 3;
    day = 1460;
  } else {
    day += 365 * (year % 4);
  }
  year /= 4;

  day += 1461 * (year % 25);
  year /= 25;

  if (day == 36524) {
    year -= 3;
    day = 146096;
  } else {
    day += 36524 * (year % 4);
  }
  year /= 4;

  day += 146097 * (year - 5);
  day += 11017;

  return ((day * 24 + dt->hour) * 60 + dt->min) * 60 + dt->sec;
}