设数列的第$n$项为$f(n)$，则根据定义有$f(n)=f(n-1)+f(n-2)$。由此易得，

$f(n) = f(1) + f(0) + f(1) + … + f(n-2)$

用wat语言（wasm）可实现求和法计算$f(n)$如下：

(module
    (func $fib (export "fib") (param $n i32) (result i32)
        (local $tmp i32)
        
        (local.set $tmp (i32.const 1))
        
        (block $break
            (br_if $break (i32.lt_s
                                (local.get $n)
                                (i32.const 2)))
            (loop $loop
                (local.set $tmp (i32.add
                                    (call $fib (i32.add
                                                    (local.get $n)
                                                    (i32.const -2)))
                                    (local.get $tmp)))
                (br_if $loop (i32.gt_s
                                (local.tee $n (i32.add (local.get $n) (i32.const -1)))
                                (i32.const 1)))
            )
        )

        local.get $tmp        

    )
)

直接用f(n)=f(n-1)+f(n-2)的逻辑，wat代码为：
(module
    (func $fib (export "fib") (param $n i32) (result i32)
        (local $tmp i32)
        
        (local.set $tmp (i32.const 1))
        
        (block $break
            (br_if $break (i32.lt_s
                                (local.get $n)
                                (i32.const 2)))
            (local.set $tmp (i32.add
                                    (call $fib (i32.add
                                                    (local.get $n)
                                                    (i32.const -2)))
                                    (call $fib (i32.add
                                                    (local.get $n)
                                                    (i32.const -1)))))
        )
        local.get $tmp        
    )
)