public String arithmetic(String instruction) {
		String[] instArray = instruction.split(" ");
		Register dest = getRegister(1, instArray);
		Register source1 = getRegister(2, instArray);
		Register source2 = getRegister(3, instArray);
		switch (instArray[0]) {
		case "ADD":
			return add(dest, source1, source2);
		case "SUB":
			return sub(dest, source1, source2);
		case "ADDI":
			return addi(dest, source1, instArray[3]);
		case "MUL":
			return mul(dest, source1, source2);
		case "NAND":
			return nand(dest, source1, source2);
		// add branch here to calculate the destination?
		}
		//registerFile.print();
		return ""; 
	}