code: func TruncateFrac(t gotime.Time, fsp int) (gotime.Time, error) {
  	if _, err := CheckFsp(fsp); err != nil {
  		return t, err
  	}
  	return t.Truncate(gotime.Duration(math.Pow10(9-fsp)) * gotime.Nanosecond), nil
  }
docs: // TruncateFrac truncates fractional seconds precision with new fsp and returns a new one.
  // 2011:11:11 10:10:10.888888 round 0 -> 2011:11:11 10:10:10
  // 2011:11:11 10:10:10.111111 round 0 -> 2011:11:11 10:10:10