/// <summary>
        /// 将16进制转换为有符号的10进制
        /// </summary>
        /// <param name="hexstr"></param>
        /// <returns></returns>
        public string ConvertHexToSIntStr(string hexstr)
        {

　　　　if (hexstr.StartsWith("0x"))
            {
                hexstr = hexstr.Substring(2);
            }

　　　　//如果不是有效的16进制字符串或者字符串长度大于16或者是空，均返回NULL

　　　if (!IsHexadecimal(hexstr) || hexstr.Length > 16 || string.IsNullOrEmpty(hexstr))
            {
                return null;
            }
            if (hexstr.Length > 8)
            {
                return Convert.ToInt64(hexstr, 16).ToString();
            }
            else  if (hexstr.Length > 4)
            {
                return Convert.ToInt32(hexstr, 16).ToString();
            }
            else
            {
                return Convert.ToInt16(hexstr, 16).ToString();
            }
        }

/// <summary>
        /// 判断是否是十六进制格式字符串
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public bool IsHexadecimal(string str)
        {
            const string PATTERN = @"[A-Fa-f0-9]+$";
            return System.Text.RegularExpressions.Regex.IsMatch(str, PATTERN);
        }