Add source for MIPS use in education

[jerrettl]

Design-Document/swim.tex

Lines 2609 to 2623 in 2a9efe1

	% TODO: Source for these operations being used in MIPS education?
	The simple ALU generally used in MIPS education (when discussing
	specifically its implementation) supports eight operations, taking a
	3-bit operation code. However, this is limited in ability, as many
	instructions that SWIM requires cannot be supported with only eight ALU
	operations. The eight-operation ALU can perform the following
	operations: \emph{add}, \emph{subtract}, \emph{unsigned compare},
	\emph{signed compare}, \emph{bitwise and}, \emph{bitwise or}, \emph{left
	shift 16}, and \emph{bitwise not}. Operations such as \emph{multiply},
	\emph{xor}, and so on, are missing. For this project, as outlined by the
	control signals in Section \ref{subsec:control-signals}, we use an
	extended version of the simple eight-operation ALU, where the operation
	code has been expanded to four bits, allowing for 16 total operations.
	The original eight are preserved, as those are commonly used in
	education, and additional operations follow after.