function dout = my_fft(din);

c=rand(1,128);% 定制512點抽樣% 
%%%%求反序，實現反序輸入，正序輸出%%%% 
c(1)=0;c(2)=64; 
for i=1:6 % log(512)-1=8% 
    c((2^i+1):2^(i+1))=c(1:2^i)+2^(6-i); 
end 

d=rand(1,128); 

for i=1:128 
    d(i)=d((c(i)+1)); 
end%完成初始值的反序% 

%%%%求出所有的蝶算指數因子%%%% 
x=rand(128,10);a=rand(1,64);q=1;w=rand(1,64); 
for o=1:64 
    w(o)=exp(-j*2*pi*(o-1)/128); 
end 

%%%%fft變換%%%% 
x(:,1)=d'; 
for k=2:8
    i=1;p=1; 
    for m=1:2^(k-2)%求出每級所需的蝶算指數因子% 
        q=(m-1)*128/(2^(k-1)); 
        a(p)=w(q+1);p=p+1; 
    end 
    for n=1:128/(2^(k-1))%對偶節點個數的確定及變換計算% 
        p=1; 
        for h=i:i+(2^(k-2)-1)
            x(h,k)=x(h,k-1)+a(p)*x(h+2^(k-2),k-1); 
            x(h+2^(k-2),k)=x(h,k-1)-a(p)*x(h+2^(k-2),k-1); 
            p=p+1; 
        end 
        i=(2^(k-1))*n+1; 
    end 
end 

dout = x(:,8)