watrbx-game-engine/App/util/Base64BinaryInputStream.cpp

#include "stdafx.h"
#include "Util/Base64BinaryInputStream.h"

#include "Rbx/Debug.h"

namespace RBX {

unsigned char Base64BinaryInputStream::decode(unsigned char charFromString) {
	if (charFromString >= 'A' && charFromString <= 'Z') {
		return charFromString - 'A';
	}
	if (charFromString >= 'a' && charFromString <= 'z') {
		return 26 + (charFromString - 'a');
	}
	if (charFromString >= '0' && charFromString <= '9') {
		return 52 + (charFromString - '0');
	}
	if (charFromString == '+') {
		return 62;
	}
	if (charFromString == '/') {
		return 63;
	}
	RBXASSERT(false);
	return 0;
}

Base64BinaryInputStream::Base64BinaryInputStream(const char* source) : 
	source(source), buffer(0), readableBitsInBuffer(0) {}

void Base64BinaryInputStream::ReadBits(unsigned char* output, size_t numBitsToRead) {
	RBXASSERT(numBitsToRead <= 8);
    RBXASSERT(numBitsToRead >= 1);

	while (numBitsToRead > readableBitsInBuffer) {
		boost::uint16_t nextValue = decode(*source);
		source++;

		// decode produced a 6 bit number. Shift that to the head (16 - 6 = 10),
		// leaving room for the readableBits
		nextValue <<= (10 - readableBitsInBuffer);
		buffer |= nextValue;
		readableBitsInBuffer += 6;
	}

	RBXASSERT(numBitsToRead <= readableBitsInBuffer);

	unsigned char tmp = buffer >> (16 - numBitsToRead);
	(*output) = tmp;
	buffer <<= numBitsToRead;
	readableBitsInBuffer -= numBitsToRead;
}

}