Question

5. Write the MIPS minimal sequence of instructions for the following C procedure code:

int array_sum (a[], b[])
                                 { int i;
                                      i =1;

for (i=1; i<100; i=i+1)

{ b[i] = D + a[i-1] + a[i] + a[i+1] ;}

                         
                                  }

Assume that:

• a and b are arrays of words and the base address of “a” is in $a0 and the base address of “b” is in $a1,
• Register $S1 is associated with variable i.
• “D” is in register $S0 and

Answer 1

C code
int array_sum (a[], b[]) {
   int i;
        i =1;
   for (i=1; i<100; i=i+1){
   b[i] = D + a[i-1] + a[i] + a[i+1] ;
   }
}

$a0 = base address of array a[]
$a1 = base address of array b[]
$s1 = i
$s0 = D

MIPS code
addi    $s1, $0, 1   //i = 1
addi     $t0, $a0, 4   //$t0 = &a[1]
addi     $t1, $a1, 4   //$t1 = &b[1]

Loop:  
   slti    $t2, $s1, 100   //set $t2 when (i<100)
   beq    $t2, $0, Exit   //if($t2 == 0) branch to Exit
   lw    $t2, -4($t0)   //$t2 = a[i-1]
   lw    $t3, 0($t0)   //$t3 = a[i]
   add    $t2, $t2, $t3   //$t2 = a[i-1] + a[i]
   lw    $t3, 4($t0)   //$t3 = a[i+1]
   add    $t2, $t2, $t3   //$t2 = a[i-1] + a[i] + a[i+1]
   add    $t2, $t2, $s0   //$t2 = D + a[i-1] + a[i] + a[i+1]
   sw    $t2, 0($t1)   //b[i] = D + a[i-1] + a[i] + a[i+1]
   addi    $t0, $t0 ,4   //$t0 = $a[i+1]
   addi    $t1, $t1 ,4   //$t1 = $b[i+1]  
   addi    $s1, $s1, 1   //i = i+1
   j    Loop       //Jump to Loop
Exit: