Trace each program by writing the contents of each relevant register after the execution of each instruction. In the case of a loop, show the contents of each relevant register for the first two iterations and the last one.

Program$1($add$.$asm$)$:

$.$data

x: $.$word $0$

y: $.$word $0$

z: $.$word $0$

nl: $.$asciiz $"$

$"$

$.$text

main:

li $v$0,5$ # Read x

syscall

la $t$0,$ x

sw $v$0,0($$t$0)$

li $v$0,5$ # Read y

syscall

la $t$0,$ y

sw $v$0,0($$t$0)$

la $t$0,$ x # z $=$ x $+$ y

lw $t$1,0($$t$0)$

lw $t$2,4($$t$0)$

add $t$3,$ $t$1,$ $t$2$

la $t$0,$ z

sw $t$3,0($$t$0)$

li $v$0,1$ # Print z

lw $a$0,0($$t$0)$

syscall

li $v$0,4$

la $a$0,$ nl

syscall

la $t$0,$ x

lw $t$1,0($$t$0)$

lw $t$2,4($$t$0)$

sub $t$3,$ $t$1,$ $t$2$

sw $t$3,8($$t$0)$

li $v$0,1$

lw $a$0,8($$t$0)$

syscall

li $v$0,4$

la $a$0,$ nl

syscall

li $v$0,10$ # Exit

syscall

Program $2($countdown$.$asm$)$:

$.$data

cstart:

$.$word $10$

nl:

$.$asciiz $"$

$"$

$.$text

main:

la $t$0,$ cstart # step $1$: Load counter

lw $s$0,0($$t$0)$

loop:

li $v$0,1$ # step $2$: Print counter

or $a$0,$ $s$0,$ $zero

syscall

li $v$0,4$ # Print newline

la $a$0,$ nl

syscall

bne $s$0,$ $zero, continue # If counter $!=0,$ go to continue

li $v$0,10$ # exit

syscall

continue:

addi $s$0,$ $s$0,-1$ # step $4$: decrement counter

b loop # step $5$: go to $2$