fibo.wat

(module
  (func (export "fibo") (param $index i32) (result i32)
    (local $a i32)
    (local $b i32)
    (local $c i32)

    (local.set $a (i32.const 1))
    (local.set $b (i32.const 0))

    (loop $fibo-loop
      (if
        (i32.ge_s (local.get $index) (i32.const 0))
        (then
          (local.set $c (i32.add (local.get $a) (local.get $b)))
          (local.set $a (local.get $b))
          (local.set $b (local.get $c))

          (local.set $index (i32.sub (local.get $index) (i32.const 1)))

          (br $fibo-loop)
        )
      )
    )

    (local.get $b)
  )
)