Arm fib

.data
n: .word 6
res: .word -1
.text
.global main

main:
    ldr r0, =n
    ldr r0, [r0]
    mov r1, r0
    bl fib
    ldr r3, =res
    str r0, [r3]
    b end

fib:
    mov r1, #0
    mov r2, #1
    loop:
        mov r3, r1
        add r1, r1, r2
        mov r2, r3
        subs r0,r0,#1
        bne loop
        mov r0, r1
        bx lr

end:
    mov lr, #0
    bx lr