CODEWITHSUNDEEP
arraysassemblymips
Jordan Lacob
Jordan Lacob

Reputation: 31

MIPS - Help initializing array

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.

Upvotes: 1

Views: 2469

Answers (1)

Alain Merigot
Alain Merigot

Reputation: 11567

There are several problems with your code.

  1. 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 .

  2. You do not increment the array pointer in $t3

  3. 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

Upvotes: 2

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