code: func period2Month(period uint64) uint64 {
  	if period == 0 {
  		return 0
  	}
  
  	year, month := period/100, period%100
  	if year < 70 {
  		year += 2000
  	} else if year < 100 {
  		year += 1900
  	}
  
  	return year*12 + month - 1
  }
docs: // period2Month converts a period to months, in which period is represented in the format of YYMM or YYYYMM.
  // Note that the period argument is not a date value.