Question

Hey, I am confused about the following MIPS questions - could you also provide an explanation with your answer?

Thank you!

1. What is the value in $t1 when the sw instruction is executed? (i.e. what value is stored in result)

li $t1, 0

li $t2, 1

li $t3, 10

loop:

bgt $t2, $t3, end_loop

mul $t1, $t1, $t2

addi $t2, $t2, 1

j loop

end_loop:

sw $t1, result

2.

(a) If the label job is at 0x00401000, what value is contained in register $ra immediately after the execution of the jal instruction on the spim virtual machine?

0x00400200   li  $a0, 42
0x00400204   jal job
0x00400208   nop
0x0040020C   sw  $v0, x

(b) and then which of the single SPIM pseudo-instructions below are the following three instructions equivalent to:

add $t1, $0, $0
lui $t1, 0x4321
ori $t1, $t1, 0x8765

a. li $t1, 0x87654321
b.	li $t1, 0x43218765
c.	lw $t1, 0x8765
d.	addi $t1, 0x8765, 0x4321
e.	None of the other options is correct

3. Which C definition below is equivalent to the following SPIM directive?

vec: .word 1, 2, 3, 4, 5

Answer 1

Please find the answers below:::

1)

In the given code, Inside loop value is getting multiplied to t1 all the time, As t1 contains zero and mutiplication with it results zero, It will have zero all the time as result, Hence same zero will be stored to result using  sw $t1, result.

.data
result : .word 0
.text
li $t1, 0

li $t2, 1

li $t3, 10

loop:

bgt $t2, $t3, end_loop

mul $t1, $t1, $t2 #here all the time result is getting multiplied by t1, and t1 is zero.

addi $t2, $t2, 1

j loop

end_loop:

sw $t1, result

2)

jal stores the address of next instruction from where it is getting called into $ra, So as

0x00400204   jal job 

above line calling jal, The address of $ra will be  0x00400208 that is the next instruction's address.

3)

add $t1, $0, $0    #stores zero to t1
lui $t1, 0x4321    #stores 4321 at the upper 4 bits
ori $t1, $t1, 0x8765 #stores 8765 at the lower 4 bits.

Above instructions are equivalent to  

b.	li $t1, 0x43218765

4)

vec: .word 1, 2, 3, 4, 5

Above line actually creating an array,

So in c it will be like

int vec[] = {1,2,3,4,5};