问无论小数位数是多少，如何用固定的有效位数来格式化双位？

EN

  String result1 = 123.4567.ToString("G3");
  String result2 = 1.234567.ToString("G3");

  String result = String.Format("{0:G3}", 12.3456789);

   public static double round(double value) {
       int places = 0;
       BigDecimal bd = new BigDecimal(value);
       if(value>=100){
           places=0;
       }else if(value<=100 && value>=10){
           places = 1;
       }else{
           places = 2;
       }
        bd = bd.setScale(places,RoundingMode.UP);
      return bd.doubleValue();
    }

public static string TakeNumDigits(decimal number, int digits, NumberFormatInfo formatProvider = null)
{
    formatProvider = formatProvider ?? NumberFormatInfo.CurrentInfo;
    string num = number.ToString(formatProvider);
    if (digits >= num.Length)
        return num;

    string decSep = formatProvider.NumberDecimalSeparator;
    int decSepIndex = num.IndexOf(decSep);

    if (decSepIndex == -1 || decSepIndex + digits > num.Length)
        return num.Substring(0, digits);
    else
        return num.Substring(0, digits + decSep.Length);
}

decimal num1 = 123.4567m;
string result = TakeNumDigits(num1, 3); // 123
decimal num2 = 12.34567m;
result = TakeNumDigits(num2, 3);        // 12.3
decimal num3 = 1.234567m;
result = TakeNumDigits(num3, 3);        // 1.23