短链生成

 /// <summary>
 /// 短链生成
 /// </summary>
 public class ShortUrlBuilder
        {
            private static readonly string[] Chars = 
            { "a" , "b" , "c" , "d" , "e" , "f" , "g" , "h" ,

            "i" , "j" , "k" , "l" , "m" , "n" , "o" , "p" , "q" , "r" , "s" , "t" ,

            "u" , "v" , "w" , "x" , "y" , "z" , "0" , "1" , "2" , "3" , "4" , "5" ,

            "6" , "7" , "8" , "9" , "A" , "B" , "C" , "D" , "E" , "F" , "G" , "H" ,

            "I" , "J" , "K" , "L" , "M" , "N" , "O" , "P" , "Q" , "R" , "S" , "T" ,

            "U" , "V" , "W" , "X" , "Y" , "Z"
            };

            /// <summary>
            /// 生成指定URL的摘要
            /// </summary>
            /// <param name="url">URL</param>
            /// <returns>短链列表，任取一个存储就行。</returns>
            public static List<string> Build(string url)
            {
                var shortUrls = new List<string>();
                if (url == null)
                {
                    return shortUrls;
                }
                var hash = GetMd5(url);
                //将32个字符的md5码分成4段处理，每段8个字符
                for (int i = 0; i < 4; i++)
                {

                    int offset = i * 8;

                    string sub = hash.Substring(offset,   8);

                    long sub16 = long.Parse(sub, NumberStyles.HexNumber); //将sub当作一个16进制的数，转成long

                    // & 0X3FFFFFFF，去掉最前面的2位，只留下30位
                    sub16 &= 0X3FFFFFFF;

                    StringBuilder sb = new StringBuilder();
                    //将剩下的30位分6段处理，每段5位
                    for (int j = 0; j < 6; j++)
                    {
                        //得到一个 <= 61的数字
                        long t = sub16 & 0x0000003D;
                        sb.Append(Chars[(int)t]);

                        sub16 >>= 5;  //将sub16右移5位
                    }

                    shortUrls.Add(sb.ToString());
                }
                return shortUrls;
            }

            /// <summary>
            /// MD5加密
            /// </summary>
            /// <param name="myString">原始字符串</param>
            /// <param name="salt">盐</param>
            /// <returns></returns>
            private static string GetMd5(string myString, string salt = "")
            {
                if (myString != null)
                {
                    var array = myString.ToCharArray();
                    Array.Reverse(array);
                    myString = $"{new string(array)}+{{{salt}}}";

#if DEBUG
                    Debugger.Log(1, "2", $"自定义消息：{myString}
");
#endif
                    MD5 md5 = MD5.Create();
                    byte[] bs = Encoding.UTF8.GetBytes(myString);
                    byte[] hs = md5.ComputeHash(bs);
                    StringBuilder sb = new StringBuilder();
                    foreach (byte b in hs)
                    {
                        // 以十六进制格式格式化  
                        sb.Append(b.ToString("x2"));
                    }
                    return sb.ToString();

                }
                return null;
            }
        }