号码字符串与BCD编码互转 c#

/// <summary>
        /// 把号码用BCD进行压缩编码。
        /// </summary>
        /// <param name="Num8BitByte">The num8 bit byte.</param>
        /// <returns></returns>
        public static byte[] ByteArrayToBCD(byte[] Num8BitByte)//8位的ascii码
        {
            byte[] Num4bitByte = new byte[8];

            Num4bitByte = BitConverter.GetBytes(0xffffffffffffffff);
            for (int i = 0; i<Num8BitByte.Length; i++)
            {
                byte num =Convert.ToByte(Num8BitByte[i] - 0x30);
                if (i % 2 == 0)
                {
                    Num4bitByte[i / 2] = Convert.ToByte((Num4bitByte[i / 2] & 0xF0) | num);
                }
                else
                {
                    Num4bitByte[i / 2] = Convert.ToByte((Num4bitByte[i / 2] &0x0F)| (num << 4));
                }
                  
            }
            
            return Num4bitByte;
        }

        /// <summary>
        /// BCDs to string.
        /// </summary>
        /// <param name="bcdNum">The BCD num.</param>
        /// <returns></returns>
        public static string bcdToString(byte[] bcdNum)
        {
            string retString="";
            byte[] byteChar = new byte[bcdNum.Length];
            byteChar = BitConverter.GetBytes(0xffffffffffffffff);
            byte tempHigh=0,tempLow=0;
            int i = 0;
            while (tempHigh != 0x0F && tempLow != 0xF0)
            {
                tempHigh = Convert.ToByte(bcdNum[i] & 0xF0);//取出高四位；
                tempHigh = Convert.ToByte(tempHigh >> 4);
                tempLow = Convert.ToByte((bcdNum[i] & 0x0F) << 4);
                byteChar[i] = Convert.ToByte(tempLow | tempHigh);
                i++;
            } 
            string[] HexString=BitConverter.ToString(byteChar).Trim().Split('-');
            foreach (string str in HexString)
            {
                retString += str.Trim();
            }
            int LastIndex = retString.IndexOf('F');
            return retString = retString.Substring(0, LastIndex);
        }