BitBuffer v2

BitBuffer.java

public class BitBuffer {
	private ByteBuffer buffer;

	private int readByteIndex;

	private int readBitIndex;

	private List<ToLongBiFunction<ByteBuf, Integer>> readFunctions = Arrays.asList(
		(buf, index) -> buf.readByte(index), // 1 byte
		(buf, index) -> buf.readShort(index), // 2 bytes
		(buf, index) -> buf.readInt(index), // 3 bytes
		(buf, index) -> buf.readInt(index), // 4 bytes
		(buf, index) -> buf.readLong(index), // 5 bytes
		(buf, index) -> buf.readLong(index), // 6 bytes
		(buf, index) -> buf.readLong(index), // 7 bytes
		(buf, index) -> buf.readLong(index) // 8 bytes
	);

	private static final int[] MASK = {
		0b00000001,
		0b00000011,
		0b00000111,
		0b00001111,
		0b00011111,
		0b00111111,
		0b01111111,
		0b11111111,
	};

	public long readBits(int bitSize) {
		// TODO: check capacity
		int size = (int) Math.ceil(bitSize / 8.0);
		long data = readFunctions.get(size - 1).apply(buffer);
		if (readBitIndex > 0) { // O shat, we have overlap
			data >>= readBitIndex; // Scrap those damn bytes
			
			// Max overflow is one byte
			long last = buffer.readByte();
			last &= MASK[readBitIndex];
			last <<= (bitSize - readBitIndex);
			data |= last;
		}
		readByteIndex += (bitSize / 8);
		readBitIndex += (bitSize % 8);
		if (readBitIndex >= 8) {
			readBitIndex -= 8;
			readByteIndex++;
		}
	}
}