Past exam of the year 1 of the computer science course of the University of Oxford / 2015 / Digital systems, linear algebra, introduction to formal proof / 6 / b / Solution

Use two zero-address instructions for indirect access to computer memory. Define load to replace the top memory address by the value at that address, and define store to pop a value followed by the address just beneath it:Both have no encoded address operand; the stack supplies it. If the known fixed memory addresses of the variables are $p_x,p_y$, implement the assignment withThe successive stack suffixes are $p_x$, then $p_x,p_y$, then $p_x,M[p_y]$, then empty. HenceThe surrounding stack is restored. Other store conventions are possible, but the operand order must be stated and used consistently.