Method ProcessData

src/cryptopp/strciphr.cpp:67–123

template <class S>
void AdditiveCipherTemplate<S>::ProcessData(byte *outString, const byte *inString, size_t length)
{
	if (m_leftOver > 0)
	{
		size_t len = STDMIN(m_leftOver, length);
		xorbuf(outString, inString, KeystreamBufferEnd()-m_leftOver, len);
		length -= len;
		m_leftOver -= len;
		inString += len;
		outString += len;

		if (!length)
			return;
	}
	CRYPTOPP_ASSERT(m_leftOver == 0);

	PolicyInterface &policy = this->AccessPolicy();
	unsigned int bytesPerIteration = policy.GetBytesPerIteration();

	if (policy.CanOperateKeystream() && length >= bytesPerIteration)
	{
		size_t iterations = length / bytesPerIteration;
		unsigned int alignment = policy.GetAlignment();
		KeystreamOperation operation = KeystreamOperation((IsAlignedOn(inString, alignment) * 2) | (int)IsAlignedOn(outString, alignment));

		policy.OperateKeystream(operation, outString, inString, iterations);

		inString += iterations * bytesPerIteration;
		outString += iterations * bytesPerIteration;
		length -= iterations * bytesPerIteration;

		if (!length)
			return;
	}

	size_t bufferByteSize = m_buffer.size();
	size_t bufferIterations = bufferByteSize / bytesPerIteration;

	while (length >= bufferByteSize)
	{
		policy.WriteKeystream(m_buffer, bufferIterations);
		xorbuf(outString, inString, KeystreamBufferBegin(), bufferByteSize);
		length -= bufferByteSize;
		inString += bufferByteSize;
		outString += bufferByteSize;
	}

	if (length > 0)
	{
		bufferByteSize = RoundUpToMultipleOf(length, bytesPerIteration);
		bufferIterations = bufferByteSize / bytesPerIteration;

		policy.WriteKeystream(KeystreamBufferEnd()-bufferByteSize, bufferIterations);
		xorbuf(outString, inString, KeystreamBufferEnd()-bufferByteSize, length);
		m_leftOver = bufferByteSize - length;
	}
}