Integer Arrays in MIPS : Setting array[index] to iteration value i?

Question

I'm working on translating the below C++ code to MIPS (this is just a small portion of the program that I'm stuck on), and I understand the gist of how to set $t registers to take the array values given, but I'm completely stuck on

pos[count] = i;

I've tried sw, lw, but everytime I try these, I get address out of range exceptions/etc.

Can someone explain to me what's going wrong here? When the loop gets to pos[count] = i, I need to change pos[count] from 0xffffffff to (i) for each loop iteration. Is the error coming because I need to adjust for the -1's in pos[] ?

I'm completely lost and haven't been able to find any explanations that are similar enough to this problem.

(Apologies for the formatting, because MIPS has so many tabbed lines, the formatting for posting here is exceptionally wacky)

    .data
x:  .word   0
    .word   0
    .word   0
    .word   0
    .word   0
    .word   0
    .word   0
    .word   0
    .word   0
    .word   0
pos:    .word   -1
        .word   -1
        .word   -1
        .word   -1
        .word   -1
        .word   -1
        .word   -1
        .word   -1
        .word   -1
        .word   -1
d:      .word   73
        .word   47
        .word   23
        .word   26
        .word   67
        .word   99
        .word   13
        .word   53
        .word   1
        .word   97

sp: .asciiz " "
endl:   .asciiz "\n"

# $s0   count
# $s1   key
# $s2   i

        .text

main:   addi    $s0, $0, 0  #  int count = 0;
        addi    $s1, $0, 24         #  int key = 24;
        addi    $s2, $0, 0
        la  $s3, d
        la  $s4, pos
        la  $s5, x
                       #  for (int i=0; i<10; i++) {
loop:   mul     $t0, $s2, 4 #    if (d[i] >= key) {
        add     $t0, $t0, $s3
        lw  $t0, ($t0)

            blt     $t0, $s1, loop1

            sll     $t1, $s0, 2     # $t1 = count * sizeof(int)
            addu    $t2, $s4, $t1   # $t2 = &pos[count];
            lw      $t2, ($t2)  # $t2 = pos[count];

            add     $t3, $s5, $t1   # $t3 = &x[count];
            lw      $t3, ($t3)  # $t3 = x[count];


            sw    $s2, ($t2)            #      pos[count] = i;
                    #      x[count] = d[i];

loop1:     addi    $s2, $s2, 1     # i++;
           addi    $s0, $s0, 1     # count++;
                    #    }
                    #  }

Here's the C++ code equivalent:

#include <iostream>
using namespace std;

int x[10] = {0};
int pos[10] = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1};
int d[10] = {73, 47, 23, 26, 67, 99, 13, 53, 1, 97};
int main() {

int count = 0;
int key = 24;
for (int i=0; i<10; i++) {
   if (d[i] >= key) {
     pos[count] = i;
     x[count] = d[i];
      count++;
  }
 }

for (int i=0; i<10; i++) {
    if (pos[i] < 0)
      break;
     cout << pos[i] << " " << x[i] << endl;
    }

 }

I can't make heads or tails of this. It would be helpful if you showed what C++ code you are trying to duplicate, and then we would know what this is supposed to do. — Konrad Lindenbach
– Konrad Lindenbach, Commented Sep 30, 2013 at 20:16
Gotcha. I just added the C++ equivalent more clearly at the bottom of the post. My main problem is translating pos[count] = i; and x[count] = d[i]; to MIPS — blunatic
– blunatic, Commented Sep 30, 2013 at 20:55

Jester · Accepted Answer · 2013-09-30 22:40:00Z

2

This part is wrong:

lw      $t2, ($t2)  # $t2 = pos[count];
add     $t3, $s5, $t1   # $t3 = &x[count];
lw      $t3, ($t3)  # $t3 = x[count];
sw    $s2, ($t2)    #      pos[count] = i;

Why are you loading pos[count] and x[count] when you want to write to both? Not only is this unnecessary, it will destroy $t2 and $t3 so when you really want to write, they will no longer be valid.

Also, the end of the loop is wrong, the count++ should be inside the condition. For that you will need to swap the last two lines (including the label).

A slightly cleaned up version could look like:

    .data
x:      .word   0, 0, 0, 0, 0, 0, 0, 0, 0, 0
pos:    .word   -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
d:      .word   73, 47, 23, 26, 67, 99, 13, 53, 1, 97

# $s0   count
# $s1   key
# $s2   i

        .text
.globl main
main:   addi    $s0, $0, 0      #  int count = 0;
        addi    $s1, $0, 24     #  int key = 24;
        addi    $s2, $0, 0      #  int i = 0;
#  for (int i=0; i<10; i++) {
loop:   sll     $t0, $s2, 2     # $t0 = i * sizeof(int)
        lw      $t0, d($t0)     # $t0 = d[i]
        blt     $t0, $s1, loop1 # if (d[i] < key)

        sll     $t1, $s0, 2     # $t1 = count * sizeof(int)
        sw      $s2, pos($t1)   # pos[count] = i
        sw      $t0, x($t1)     # x[count] = d[i]
        addi    $s0, $s0, 1     # count++;

loop1:  addi    $s2, $s2, 1     # i++;
        blt $s2, 10, loop

answered Sep 30, 2013 at 22:40

Jester

59.4k4 gold badges89 silver badges131 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

blunatic Over a year ago

Thank you so much, you don't know how grateful I am. Been tinkering with this problem now for about two days straight. The load part I was given in the problem setup, so I thought I was stuck using only that type of loading an address: thus, I didn't know you could do d($t0), for example.

Konrad Lindenbach Over a year ago

On the vein of cleaning up, may I suggest x: .word 0:10 y: .word -1:10

ak47 · Accepted Answer · 2014-04-07 02:21:23Z

0

int count(int a[], int n, int x){ int res = 0; int i = 0; for(i = 0; i != n; i++) if(a[i] == x) res = res + 1; return res; }

Write a MIPS assembly program that will make use of the function count above as follows:  Hard-code the following 10 values into array a: 128, 10, 23, 12, 128, 9, 220, 46, 128, 5  Hard-code n = 10  Prompt the user to enter a value as follows: “Please enter an integer value”  Read the integer value and store it (lets call it x)  Call the function count with the following arguments: count(a, 10, x)  Output the results as follows: “The number of times x appears in the list is res times”  Exit the program

answered Apr 7, 2014 at 2:21

ak47

1

Collectives™ on Stack Overflow

Integer Arrays in MIPS : Setting array[index] to iteration value i?

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related