Arithmetic: multiplication
	UB multiplication also follows the same rules as ordinary arithmetic
		carry		0	1	1	1	0	0			decimal
							0	1	0	1		5
							0	1	1	1		7
							0	1	0	1
						0	1	0	1
					0	1	0	1
				0	0	0	0
		result		0	1	0	0	0	1	1		35
	Notice that the operations can be carried out using just add and shift
	2C multiplication: sign bit must be extended to get proper answer
		carry	2	2	2	1	1	0	0
			1	1	1	1	1	1	0	1		-3
							0	1	1	1		7
			1	1	1	1	1	1	0	1
			1	1	1	1	1	0	1
			1	1	1	1	0	1
			0	0	0	0	0
		result	1	1	1	0	1	0	1	1		-21