Question

2.29 The following is the C codes and the translated MIPS codes. Assume that the C-level integers t1 and a0 are held in register $t1 and $a0, and $s0 holds the base address of the integer MemArray.

void foo () {

int MemArray[100] = { 96, 98, 63, 69, 42, 27, 16, 6, 47, 74, 44, 33, 76, 7, 88, 33, 80, 86, 86, 64, 17, 67, 60, 51, 2, 61, 93, 87, 49, 98, 24, 98, 30, 65, 2, 26, 65, 28, 66, 84, 14, 4, 50, 27, 61, 27, 80, 75, 47, 19, 57, 6, 48, 74, 62, 60, 41, 7, 35, 77, 76, 84, 14, 34, 56, 52, 15, 55, 45, 47, 20, 55, 81, 99, 89, 65, 42, 39, 56, 20, 77, 58, 35, 55, 22, 4, 45, 22, 4, 77, 91, 53, 26, 42, 56, 42, 96, 71, 99, 82};

int a0=0;

for (int t1=0; t1<100; t1++) {

    a0 += MemArray[t1];

}

cout << a0 << endl;

}

           

.data

MemArray: .word    96, 98, 63, 69, 42, 27, 16, 6, 47, 74, 44, 33, 76, 7, 88, 33, 80, 86, 86, 64, 17, 67, 60, 51, 2, 61, 93, 87, 49, 98, 24, 98, 30, 65, 2, 26, 65, 28, 66, 84, 14, 4, 50, 27, 61, 27, 80, 75, 47, 19, 57, 6, 48, 74, 62, 60, 41, 7, 35, 77, 76, 84, 14, 34, 56, 52, 15, 55, 45, 47, 20, 55, 81, 99, 89, 65, 42, 39, 56, 20, 77, 58, 35, 55, 22, 4, 45, 22, 4, 77, 91, 53, 26, 42, 56, 42, 96, 71, 99, 82

.text

         la       $s0, MemArray    # s0 = base address of MemArray

         add   $a0, $0, $0         # a0 = 0

         add   $t1, $0, $0           # t1 = 0

LOOP:

         lw    $s1, 0($s0)           # s1 = *MemArray

         add   $a0, $a0,   $s1     # a0 += *MemArray

         addi $s0, $s0,   4         # MemArray++

         addi $t1, $t1,   1        # t1++

         slti    $t2, $t1,   100    # if (t1<100) go to LOOP

         bne   $t2, $0,    LOOP          #

RESULT:

         li       $v0, 1

         syscall

                                               

Rewrite the loop from Exercise 2.29 with memory pointers directly (instead of array) index to reduce the number of MIPS instructions executed.

Hints: You may use the following C codes and translate them to the MIPS codes.

int a0=0;

for ( int* p = MemArray; p<MemArray+100; p++) {

         a0 += *p;

}

         cout << a0 << endl;

}

Answer 1

Please find the updated code below::

.data

MemArray: .word 96, 98, 63, 69, 42, 27, 16, 6, 47, 74, 44, 33, 76, 7, 88, 33, 80, 86, 86, 64, 17, 67, 60, 51, 2, 61, 93, 87, 49, 98, 24, 98, 30, 65, 2, 26, 65, 28, 66, 84, 14, 4, 50, 27, 61, 27, 80, 75, 47, 19, 57, 6, 48, 74, 62, 60, 41, 7, 35, 77, 76, 84, 14, 34, 56, 52, 15, 55, 45, 47, 20, 55, 81, 99, 89, 65, 42, 39, 56, 20, 77, 58, 35, 55, 22, 4, 45, 22, 4, 77, 91, 53, 26, 42, 56, 42, 96, 71, 99, 82

.text

add $a0, $0, $0 # a0 = 0

add $t1, $0, $0 # t1 = 0

LOOP:

mul $s0, $t1, 4 # get index directly
  
lw $s1, MemArray($s0) # s1 = *MemArray

add $a0, $a0, $s1 # a0 += *MemArray

addi $t1, $t1, 1 # t1++

blt $t1,100,LOOP

RESULT:

li $v0, 1

syscall

output::