MIPS subroutine passing parameters by reference

Question

I have this MIPS code that do some adds using subroutines parameters passed by value

    .data # Data zone
dato1: .word 1
dato2: .word 3
dato3: .word 5
dato4: .word 4
res1: .space 4
res2: .space 4
    .text # Code Zone
    # main Code
main: lw $a0, dato1($0)
lw $a1, dato2($0)
firstcall: jal suma
sw $v0, res1($0)
lw $a0, dato3($0)
lw $a1, dato4($0)
secondcall: jal suma
sw $v0, res2($0)
j fin #End

suma: add $v0, $a0, $a1
jr $ra

fin:
li $v0, 10
syscall

But now I need to "translate it" so the sobroutine uses parameters by reference.

Any ideas?

Answer 1

Ok, fixed. I thought la standed for "load array", but it's load address.

So the new code is

    .data # Data zone
dato1: .word 1
dato2: .word 3
dato3: .word 5
dato4: .word 4
res1: .space 4
res2: .space 4
    .text # Code zone
    # Main program
main:
la $a0, dato1
la $a1, dato2
la $a3, res1

firstcall: jal suma
la $a0, dato3
la $a1, dato4
la $a3, res2
secondcall: jal suma
j fin 
suma:
lw $a0, 0($a0)
lw $a1, 0($a1)
add $v0, $a0, $a1
sw $v0, 0($a2)
jr $ra

fin:
li $v0, 10
syscall

Now this should work.