function [y,N]=dfft(x)

for m=1:inf  %找x的長(zhǎng)度對(duì)應(yīng)的2的最低冪次
    if 2^m>=length(x);break;end
end 

N=2^m;

if length(x<N)
  x1=[x,zeros(1,N-length(x))];%補(bǔ)零
end

y=daoxu(x1,N); %調(diào)用倒序排列函數(shù)

for mm=1:m % 做m級(jí)蝶形運(yùn)算，每一級(jí)都有2^(mm-1)個(gè)蝶形結(jié) 
Nz=2^mm;u=1;  
WN=exp(-i*2*pi/Nz); 
for j=1:Nz/2 % 蝶形運(yùn)算過程,在進(jìn)行第mm級(jí)運(yùn)算時(shí)需要2^(mm-1)個(gè) 蝶形 
for k=j:Nz:N % 蝶形運(yùn)算的跨越間隔為Nz=2^mm 
kp=k+Nz/2;  %k,kp為碟形運(yùn)算的對(duì)應(yīng)單元下標(biāo)
t=y(kp)*u; % 蝶形運(yùn)算的乘積項(xiàng) 
y(kp)=y(k)-t;
y(k)=y(k)+t; 
end 
u=u*WN; 
end 
end