.text
    .global fib
fib:
    cmp x0, 1
    b.le fib_end
    mov x1, 0
    mov x2, 1
fib_rec:
    add x3, x1, x2
    mov x1, x2
    mov x2, x3
    sub x0, x0, 1
    cbnz x0, fib_rec
    mov x0, x1
fib_end:
    ret