Question

3. Consider the following MIPS loop: LOOP: Comment slt $t2, 0, Sti beg $t2, 0, exit addi $t1, $t1,-1 addi Sal, $31, 2 TOOP exit: a. (5 pts) Write comments for each line, at the right side of above table. b. (12 pts) Write the equivalent C code. Assume that the registers $sland $t1 is associated with integers "a" and "I", respectively. c. (3pts) Assume that the register $t1 is initialized to the value 2. What is the value in register Ssl after the code exit? Assuming $sl is initially zero

please explain fully

Answer 1

a)

LOOP:	Comments
slt $t2,0,$t1	if 0 is less than $t1, set $t2=1 otherwise $t2=0
beq $t2,0,exit	if two are equal ie. if 0==$t2 then branch to target i.e. exit
addi $t1,$t1,-1	means $t1=$t1-1 i.e. adding sign extended immediate value
addi $s1,$s1,2	means $s1=$s1+2 i.e. adding sign extended immediate value
j Loop	means goto Loop until exit branch executed
exit:	another branch exit which comes when $t2==0

b) Equivalent C code-

Let take $t2 as j, $t1 as i and $s1 as a.

#include <stdio.h>

int main()
{
    int j,i=2;
    int a=0;
    do 
    {
        if(0<i)
        {
            j=1;
        }
        else{j=0;}
        i=i-1;
        a=a+2;
    }while(j!=0);
    printf("%d ", a);
    return 0;
}

c)

Dry run is shown below-

i	a	j
2	0	1
1	2	1
0	4	1
0	6	0

The value of a=6 when i=2 and a=0 and execution of code as shown in the screenshot below.

Run Debug Stop Share Save {} Beautify Language C main.c 8 9 #include <stdio.h> 10 11 int main() 12 { 13 int j,i=2; 14 int a=0; 15 do 16 { 17 if(@<i)| 18 { 19 j=1; 20 } 21 else{j=0;} 22 i=i-1; 23 a=a+2; 24 }while(j!=0); 25 printf("%d ", a); 26 return 0; 27 } 28 input 6 ... Program finished with exit code 0 Press ENTER to exit console.