code: private long yearToDayOfEpoch(long year)
    {
      if (year > 0) {
        year -= 1601;
        return (365 * year + year / 4 - year / 100 + year / 400 -
                ((1970 - 1601) * 365 + (1970 - 1601) / 4 - 3));
      } else {
        year = 2000 - year;
  
        return ((2000 - 1970) * 365 + (2000 - 1970) / 4 -
                (365 * year + year / 4 - year / 100 + year / 400));
      }
    }
docs: Based on the year, return the number of days since the epoch.