Arithmetic/logical: summary
					R-type	I-type
	Arithmetic	Add unsigned			addu	addiu
		Add signed			add	addi
		Subtract unsigned			subu
		Subtract signed			sub
	Boolean	AND			and	andi
		OR			or	ori
		Negated OR			nor
		Exclusive OR			xor	xori
	Shift (logical)	Left constant			sll
		Right constant			srl
		Left variable			sllv
		Right variable			srlv
	Shift (arithmetic)	Right constant			sra
		Right variable			srav