C#ASCII-base85编码解码

    public class ASCII85
    {
        static List<byte> whiteSpaces = new List<byte>(new byte[] { 0, 9, 10, 12, 13, 32 });

        public static byte[] Encode(byte[] bs)
        {
            using (MemoryStream source = new MemoryStream(bs))
            {
                using (MemoryStream target = new MemoryStream())
                {
                    Encode(source, target);
                    return target.ToArray();
                }
            }
        }

        public static byte[] Decode(byte[] bs)
        {
            using (MemoryStream source = new MemoryStream(bs))
            {
                using (MemoryStream target = new MemoryStream())
                {
                    Decode(source, target);
                    return target.ToArray();
                }
            }
        }

        public static byte[] Encode(string str)
        {
            byte[] bs = Encode(Encoding.UTF8.GetBytes(str));
            return bs;
        }
        public static byte[] Decode(string str)
        {
            byte[] bs = Decode(Encoding.UTF8.GetBytes(str));
            return bs;
        }

        public static void Decode(Stream encoded, Stream decoded)
        {
            //过滤<~...~>
            bool trimStart = false, trimEnd = false;
            encoded.Position = 0;
            if (encoded.ReadByte() == (byte)'<' && encoded.ReadByte() == (byte)'~')
                trimStart = true;
            encoded.Position = encoded.Length - 2;
            if (encoded.ReadByte() == (byte)'~' && encoded.ReadByte() == (byte)'>')
                trimEnd = true;
            encoded.Position = trimStart ? 2 : 0;
            long length = trimEnd ? encoded.Length - 2 : encoded.Length;

            byte[] bs;
            uint[] bs1;
            int t, len;
            while (encoded.Position < length)
            {
                if (encoded.ReadByte() == 122)
                {
                    decoded.Write(new byte[4], 0, 4);
                    continue;
                }

                len = 0;
                bs1 = new uint[5];
                encoded.Position--;
                for (int i = 0; i < 5; i++)
                {
                    t = SkipIfWhiteSpace(encoded);
                    if (t < 0)
                        bs1[i] = 84;
                    else
                    {
                        bs1[i] = (uint)t - 33;
                        len++;
                    }
                }

                uint value = bs1[0] * 85 * 85 * 85 * 85 +
                            bs1[1] * 85 * 85 * 85 +
                            bs1[2] * 85 * 85 +
                            bs1[3] * 85 +
                            bs1[4];
                bs = BitConverter.GetBytes(value).Reverse().Take(len - 1).ToArray();
                decoded.Write(bs, 0, bs.Count());
            }
        }

        public static void Encode(Stream source, Stream target)
        {
            source.Position = 0;
            target.Position = 0;

            byte[] bs = new byte[5];
            int len = 0, c1, c2, c3, c4;
            while (source.Position < source.Length)
            {
                c1 = source.ReadByte();
                c2 = source.ReadByte();
                c3 = source.ReadByte();
                c4 = source.ReadByte();

                len = 1;
                if (c2 > -1) len++; else c2 = 0;
                if (c3 > -1) len++; else c3 = 0;
                if (c4 > -1) len++; else c4 = 0;

                if ((c1 | c2 | c3 | c4) == 0)
                {
                    target.WriteByte((byte)122);
                    continue;
                }


                uint a = (uint)((c1 << 24) | (c2 << 16) | (c3 << 8) | (c4));
                uint b;
                for (int i = 0; i < 5; i++)
                {
                    b = a % 85;
                    a = a / 85;
                    bs[4 - i] = ((byte)(b + 33));
                }
                for (int i = 0; i < len + 1; i++)
                    target.WriteByte(bs[i]);
            }
        }
        
        //跳过空白字节返回字节
        static int SkipIfWhiteSpace(Stream encoded)
        {
            int r = 0;
            do
            {
                r = encoded.ReadByte();
            }
            while (r > -1 && whiteSpaces.Contains((byte)r));
            return r;
        }
    }

调用方式:

string str = "ABCDefg一二三四五[调皮]🐶";
string encode = ASCII85.Encode(str); //5sdq,AS,T9\:EYON9%L*jdVb#\s-F_Y_2,-Y$LOhOL>
string decode = ASCII85.Decode(encode);  //ABCDefg一二三四五[调皮]🐶