docs: protected long computeOffset(final long t, final DateTimeZone tz)
    {
      // start is the beginning of the last period ending within dataInterval
      long start = dataInterval.getEndMillis() - periodMillis;
      long startOffset = start % periodMillis - originMillis % periodMillis;
      if (startOffset < 0) {
        startOffset += periodMillis;
      }
  
      start -= startOffset;
  
      // tOffset is the offset time t within the last period
      long tOffset = t % periodMillis - originMillis % periodMillis;
      if (tOffset < 0) {
        tOffset += periodMillis;
      }
      tOffset += start;
      return tOffset - t - (tz.getOffset(tOffset) - tz.getOffset(t));
    }