contar unos en binario

.data
.text
.globl main
main:
li $v0,5
syscall
move $a0,$v0

jal funcion

move $a0,$v0

li $v0,1
syscall
li $v0,10
syscall

funcion:
    beq $a0, $zero, trivial
    li $t0,1
    beq $a0,$t0, trivial

    addi $sp, $sp,-4
    sw $ra,($sp)

    addi $sp,$sp,-4
    sw $a0,($sp)

    srl $a0,$a0,1

    jal funcion

    lw $a0, ($sp)
    addi $sp,$sp,4
    andi $t0,$a0,1
    add $v0,$v0,$t0
    lw $ra, ($sp)
    addi $sp,$sp,4

    jr $ra
    trivial:

        move $v0,$a0
        jr $ra