C＃实现Base64编码与解码（二）

另一种写法：

private string Encode64(string Message)

{

char[] Base64Code = new char[]

{

'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', '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', '+', '/', '='

};

byte empty = (byte)0;

System.Collections.ArrayList byteMessage = new

System.Collections.ArrayList(System.Text.Encoding.Default.GetBytes

(Message));

System.Text.StringBuilder outmessage;

int messageLen = byteMessage.Count;

int page = messageLen / 3;

int use = 0;

if ((use = messageLen % 3) > 0)

{

for (int i = 0; i < 3 - use; i++)

byteMessage.Add(empty);

page++;

}

outmessage = new System.Text.StringBuilder(page * 4);

for (int i = 0; i < page; i++)

{

byte[] instr = new byte[3];

instr[0] = (byte)byteMessage[i * 3];

instr[1] = (byte)byteMessage[i * 3 + 1];

instr[2] = (byte)byteMessage[i * 3 + 2];

int[] outstr = new int[4];

outstr[0] = instr[0] >> 2;

outstr[1] = ((instr[0] & 0x03) << 4) ^ (instr[1] >> 4);

if (!instr[1].Equals(empty))

outstr[2] = ((instr[1] & 0x0f) << 2) ^ (instr[2] >> 6);

else

outstr[2] = 64;

if (!instr[2].Equals(empty))

outstr[3] = (instr[2] & 0x3f);

else

outstr[3] = 64;

outmessage.Append(Base64Code[outstr[0]]);

outmessage.Append(Base64Code[outstr[1]]);

outmessage.Append(Base64Code[outstr[2]]);

outmessage.Append(Base64Code[outstr[3]]);

}

return outmessage.ToString();

}

private string Decode64(string Message)

{

string Base64Code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

int page = Message.Length / 4;

System.Collections.ArrayList outMessage = new System.Collections.ArrayList(page * 3);

char[]message = Message.ToCharArray();

for (int i = 0; i < page; i++)

{

byte[]instr = new byte[4];

instr[0] = (byte)Base64Code.IndexOf(message[i * 4]);

instr[1] = (byte)Base64Code.IndexOf(message[i * 4+1]);

instr[2] = (byte)Base64Code.IndexOf(message[i * 4+2]);

instr[3] = (byte)Base64Code.IndexOf(message[i * 4+3]);

byte[]outstr = new byte[3];

outstr[0] = (byte)((instr[0] << 2) ^ ((instr[1] & 0x30) >> 4));

if (instr[2] != 64)

{

outstr[1] = (byte)((instr[1] << 4) ^ ((instr[2] & 0x3c) >> 2));

}

else

{

outstr[2] = 0;

}

if (instr[3] != 64)

{

outstr[2] = (byte)((instr[2] << 6) ^ instr[3]);

}

else

{

outstr[2] = 0;

}

outMessage.Add(outstr[0]);

if (outstr[1] != 0)

outMessage.Add(outstr[1]);

if (outstr[2] != 0)

outMessage.Add(outstr[2]);

}

byte[]outbyte = (byte[])outMessage.ToArray(Type.GetType("System.Byte"));

return System.Text.Encoding.Default.GetString(outbyte);

}