private static void WriteBase64(
StringOutput writer,
byte[] data,
int offset,
int count,
bool classic,
bool padding)
{
if (writer == null)
{
throw new ArgumentNullException(nameof(writer));
}
if (offset < 0)
{
throw new ArgumentException("offset(" + offset + ") is less than " +
"0 ");
}
if (offset > data.Length)
{
throw new ArgumentException("offset(" + offset + ") is more than " +
data.Length);
}
if (count < 0)
{
throw new ArgumentException("count(" + count + ") is less than " +
"0 ");
}
if (count > data.Length)
{
throw new ArgumentException("count(" + count + ") is more than " +
data.Length);
}
if (data.Length - offset < count)
{
throw new ArgumentException("data's length minus " + offset + "(" +
(data.Length - offset) + ") is less than " + count);
}
string alphabet = classic ? Base64Classic : Base64URL;
int length = offset + count;
int i = offset;
var buffer = new byte[32];
var bufferOffset = 0;
for (i = offset; i < (length - 2); i += 3)
{
if (bufferOffset >= buffer.Length)
{
writer.WriteAscii(buffer, 0, bufferOffset);
bufferOffset = 0;
}
buffer[bufferOffset++] = (byte)alphabet[(data[i] >> 2) & 63];
buffer[bufferOffset++] = (byte)alphabet[((data[i] & 3) << 4) +
((data[i + 1] >> 4) & 15)];
buffer[bufferOffset++] = (byte)alphabet[((data[i + 1] & 15) << 2) +
((data[i +
2] >> 6) & 3)];
buffer[bufferOffset++] = (byte)alphabet[data[i + 2] & 63];
}
int lenmod3 = count % 3;
if (lenmod3 != 0)
{
if (bufferOffset >= buffer.Length)
{
writer.WriteAscii(buffer, 0, bufferOffset);
bufferOffset = 0;
}
i = length - lenmod3;
buffer[bufferOffset++] = (byte)alphabet[(data[i] >> 2) & 63];
if (lenmod3 == 2)
{
buffer[bufferOffset++] = (byte)alphabet[((data[i] & 3) << 4) +
((data[i + 1] >>
4) & 15)];
buffer[bufferOffset++] = (byte)alphabet[(data[i + 1] & 15) << 2];
if (padding)
{
buffer[bufferOffset++] = (byte)'=';
}
}
else
{
buffer[bufferOffset++] = (byte)alphabet[(data[i] & 3) << 4];
if (padding)
{
buffer[bufferOffset++] = (byte)'=';
buffer[bufferOffset++] = (byte)'=';
}
}
}
if (bufferOffset >= 0)
{
writer.WriteAscii(buffer, 0, bufferOffset);
}
}
