total 20 points
1. 10 points 
   Accumulator:
  		code	data
   load	b	3	4
   add c	3 	4
   store a	3	4
   add c	3	4
   store b	3	4
   neg		1	0
   add a	3	4
   store d	3	4
		22	28 (50)

   Stack:
   push b	3	4
   push c	3	4
   add		1	0
   dup		1	0
   pop a	3	4
   push c	3	4
   add		1	0
   dup		1	0
   pop b	3	4
   neg		1	0
   push a	3	4
   add		1	0
   push d	3	4
		27	28 (55)

   Memory-memory:  
   add a, b, c	7	12
   add b, a, c	7	12
   sub d, a, b	7	12
		21	36 (57)

   Load-store:
   load $1, b	4	4
   load $2, c	4	4
   add $3,$1,$2	3	0
   store $3, a	4	4
   add $1,$2,$3	3	0
   store $1, b	4	4
   sub $4,$3,$1 3	0
   store $4, d  4	4
   		29	20 (49)

code size efficient: memory-memory
(code+data) efficient: load-store


2. a:2 points;  b:3 points
   (a) mov 	R2, R1
       rshift 	R2, 7
       and	R2, 0x3F
   (b) and	R1, 0xFFC1FFFF	; R1=X...X 000000 X....X
       lshift   R2, 17
       and	R2, 0x003E0000	; R2=0...0 XXXXXX 0....0
       or	R1, R2

3. a:2 points;  b:3 points 
   (a) 	int log_2(int n)
       	{
	    int result;

 	    if (n==1) result=0;
	    else result=1+log_2(n/2);

	    return result;
	}

    (b) <omit>