MIPS - Help initializing array

Question

I am trying to initialize memory array to values 1, 2, 3.. 10. Though I am having a bit of trouble. Here is my work so far:

.data
myarray: .space 10
.text
la $t3, myarray  # Load the address of myarray 
addi $t2, $zero, 1  # Initialize the first data value in register.
addi $t0, $zero, 10  # Initialize loop counter $t0 to the value 10

top:

sw $t2, 0($t3)   # Copy data from register $t2 to address [ 0 +
# contents of register $t3]
    addi $t0, $t0, -1   # Decrement the loop counter
    bne $t0, $zero, top

Any help would be much appreciated.

Alain Merigot · Accepted Answer · 2019-04-02 09:11:28Z

2

There are several problems with your code.

If you use sw (store word), you assume a "word" array. Its size should be 4*10. If you wand a byte array, use sb .
You do not increment the array pointer in $t3
Same problem for the array values in $t2

.data
  myarray: .space 10
.text
    la $t3, myarray     # Load the address of myarray 
    addi $t2, $zero, 1  # Initialize the first data value in register.
    addi $t0, $zero, 10 # Initialize loop counter $t0 to the value 10
top:
    sb $t2, 0($t3)      # Copy data from register $t2 to address [ 0 +
                        # contents of register $t3]
    addi $t0, $t0,-1    # Decrement the loop counter
    addi $t3, $t3, 1    # next array element
    addi $t2, $t2, 1    # value of next array element
    bne $t0, $zero, top

As suggested by @PeterCordes, this can be optimized by merging the loop counter and the array values register to suppressed one instruction in the loop. The corresponding loop in C will be

for(i=1, ptr=array; i!=11; ptr++,i++) *ptr=i;

And the corresponding code

.data
  myarray: .space 10
.text
    la $t3, myarray     # Load the address of myarray 
    addi $t2, $zero, 1  # Initialize the first data value in register.
    addi $t0, $zero, 11 # Break the loop when array value reaches 11 
top:
    sb $t2, 0($t3)      # Copy data from register $t2 to address [ 0 +
                        # contents of register $t3]
    addi $t2, $t2, 1    # Increment array value/loop counter
    addi $t3, $t3, 1    # next array element
    bne $t0, $t2, top

edited Apr 2, 2019 at 9:11

answered Apr 1, 2019 at 18:39

Alain Merigot

11.7k3 gold badges22 silver badges33 bronze badges

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

2 Comments

Peter Cordes Over a year ago

You can use the array-element value as a loop counter, with bne $t3, $t0, top. (initialize t0 = 11 outside the loop.)

Peter Cordes Over a year ago

A more literal translation to C would be a pointer increment, so there's no i-1.

Collectives™ on Stack Overflow

MIPS - Help initializing array

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related