/// <summary>
/// Base64編碼類。
/// 將byte[]型別轉換成Base64編碼的string型別。
///</summary>
public class Base64Encoder
{
byte[] source;
int length, length2;
int blockCount;
int paddingCount;
public static Base64Encoder Encoder =new Base64Encoder();

public Base64Encoder()
{
}

private void init(byte[] input)
{
source = input;
length = input.Length;
if ((length % 3) == 0)
{
paddingCount = 0;
blockCount = length / 3;
}
else
{
paddingCount = 3 - (length % 3);
blockCount = (length + paddingCount) / 3;
}
length2 = length + paddingCount;
}

public string GetEncoded(byte[] input)
{
//初始化
init(input);

byte[] source2;
source2 = new byte[length2];

for (int x =0; x < length2; x++)
{
if (x < length)
{
source2[x] = source[x];
}
else
{
source2[x] = 0;
}
}

byte b1, b2, b3;
byte temp, temp1, temp2, temp3, temp4;
byte[] buffer = new byte[blockCount * 4];
char[] result = new char[blockCount * 4];
for (int x =0; x < blockCount; x++)
{
b1 = source2[x * 3];
b2 = source2[x * 3 + 1];
b3 = source2[x * 3 + 2];

temp1 = (byte)((b1 & 252) >> 2);

temp = (byte)((b1 & 3) << 4);
temp2 = (byte)((b2 & 240) >> 4);
temp2 += temp;

temp = (byte)((b2 & 15) << 2);
temp3 = (byte)((b3 & 192) >> 6);
temp3 += temp;

temp4 = (byte)(b3 & 63);

buffer[x * 4] = temp1;
buffer[x * 4 + 1] = temp2;
buffer[x * 4 + 2] = temp3;
buffer[x * 4 + 3] = temp4;

}

for (int x =0; x < blockCount *4; x++)
{
result[x] = sixbit2char(buffer[x]);
}


switch (paddingCount)
{
case 0:break;
case 1: result[blockCount *4 -1] = '=';break;
case 2: result[blockCount *4 -1] = '=';
result[blockCount * 4 - 2] = '=';
break;
default: break;
}
return newstring(result);
}
private char sixbit2char(byte b)
{
char[] lookupTable = new char[64]{
'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','+','/'};

if ((b >= 0) && (b <= 63))
{
return lookupTable[(int)b];
}
else
{

return '';
}
}

}