CS3421 Exam 1 Solutions

  1. 1) fetch the next instruction
    2) increment the program counter
    3) decode the instruction
    4) execute the instruction 

  2. add	$s2,$a0,$zero  (there are other solutions too)

addi	$t4,$zero,-1   (there are other solutions too)


  3. $t1 = 0xd02
$t2 = 0xff9c0f4d

  4. 44

  5. One possible solution. There are many. 
    	la	$t0,info		# load address of beginning of array
loop:
	lw	$t1,0($t0)		# load next element of info
	blt	$t1,$zero,neg		# out of loop if negative
	addi	$t1,$t1,4		# advance to next element
	b       loop                    # check next element
neg:
	la	$t1,info		# get address of beginning of array
	sub	$s0,$t0,$t1		# subtract address of negative element
	sra     $s0,$s0,2		# divide by 4
	# at this point $s0 has the value

  6. One possible solution. There are many. 
    # Parameter values are in $a0, $a1 and $a2, return value goes into $v0.
# Since no $s registers are used and there are no jal's in the code, no
# registers need to be saved.
which:
	# assume $a0 is the largest
	move    $t0,$a0
	li	$v0,0

	# if $a1 is larger, record it
	bge     $a0,$a1,skip1
	move    $t0,$a1
	li	$v0,1

skip1:
	# if $a2 is larger yet, record it
	bge	$t0,$a2,skip2
	move    $t0,$a2
	li	$v0,2

skip2:
	# return
	jr	$ra

  7. When the procedure contains a jal instruction. 

  8. 000000 10100 00010 00111 00000 100000

    
000100 00100 00101 1111111111111011


  9. sll   $a2,$t1,16

    
lw    $t9,17($sp)