Simple MIPS for loop not running - loops

Question

I'm very new to MIPs and trying to create a for loop for an assignment.
for (int i=1; i < 16; i+=2)
{
A[i] = A[i] + B[3*i]
}
With the current code I have when I try to load the value of A[i] it says fetch address not aligned on word boundary.
Here is my code:
main:
li $t0, 1 # Starting index of t0=i
lw $s7, aSize # Loop bound
la $s0, A # &A
la $s6, endA # &endA
la $s1, B # &B
loop:
#TODO: Write the loop code
addi $t3, $zero, 3 # $t3 = 3
mul $t4, $t0,$t3 # $t4 = i * 3
sll $t4, $t4, 2 # $t4 into a byte offset
add $s1, $s1, $t4 # $s1 = &B[i*3]
add $s0, $s0, $t0 # $s0 = &A[i]
lw $t1, 0($s0) # value of A[i]
lw $t2, 0($s1) # value of B[i * 3]
add $t2, $t1, $t2 # A[i] + B[i]
sw $t2, 0($s0) # A[i] = A[i] + B[i]
addi $s0, $s0, 2
addi $s1, $s1, 2
addi $t0, $t0, 1 #i++
bne $t0, $s7, loop
I'm very new to MIPs so not sure whats going on or where to even look. I appreciate any help.

Answer 1

When you do:
mul $t4, $t0,$t3 # $t4 = i * 3
You are calculating the array index [as you would in c].
But, before you can add that to the base address of the array, you need to convert this index into a byte offset. That is, you have to multiply it by 4. This can be done [as in c] with a shift left of 2.
So, after the mul, do:
sll $t4,$t4,2
You have to do this multiply/shift for all index values before adding them in.
UPDATE:
Okay that makes sense. I added that in but I'm still getting that word boundary error on the line "lw $t1, 0($s0)"
You're not showing the definition of A or B, so there could be an alignment issue.
When you do:
add $s1, $s1, $t4 # $s1 = &B[i*3]
You are modifying the original/base value of &B[0]. That's not what you want. Use a different register for the final address value (i.e. leave $s1 unchanged throughout the loop)
Do something like:
add $s3, $s1, $t4 # $s3 = &B[i*3]
lw $t2, 0($s3) # value of B[i * 3]
Adjust other similar register usage in a similar manner (i.e. you have a similar problem with the A array)
I've coded up a cleaned up version. I've not assembled nor tested it, but I think it will get you closer. This may have an off-by-one error [it's hard to tell without the entire program] as I'm not sure what aSize is.
main:
li $t0,1 # Starting index of t0=i
lw $s7,aSize # Loop bound
la $s0,A # &A
la $s6,endA # &endA
la $s1,B # &B
addi $t3,$zero,3 # $t3 = 3
loop:
# TODO: Write the loop code
mul $t4,$t0,$t3 # $t4 = i * 3
sll $t4,$t4,2 # $t4 into a byte offset
add $s3,$s1,$t4 # $s3 = &B[i*3]
sll $t4,$t0,2 # $t4 into a byte offset
add $s2,$s0,$t4 # $s2 = &A[i]
lw $t1,0($s2) # value of A[i]
lw $t2,0($s3) # value of B[i * 3]
add $t2,$t1,$t2 # A[i] + B[i]
sw $t2,0($s2) # A[i] = A[i] + B[i]
addi $t0,$t0,2 # i += 2
bne $t0,$s7,loop