public complex EE(complex b1, complex b2) //旋转因子
{
complex b3 = new complex();
b3.real = b1.real * b2.real - b1.imag * b2.imag;
b3.imag = b1.real * b2.imag + b1.imag * b2.real;
return(b3);
}
public void FFT(complex[] xin, int N) //*xin为需要FFT变换的数组，N为转换的点数
{
int f, m, LH, nm, i, k, j, L;
double p, ps;
int le, B, ip;
float pi;
complex w = new complex();
complex t = new complex();
LH = N >> 1;
f = N;
for (m = 1; (f = f >> 1) != 1; m++)
{
;
}
nm = N - 2;
j = N >> 1;
for (i = 1; i <= nm; i++) // 变址运算
{
if (i < j)
{
t = xin[j]; xin[j] = xin[i]; xin[i] = t;
}
k = LH;
while (j >= k)
{
j = j - k; k = k / 2;
}
j = j + k;
}
for (L = 1; L <= m; L++) //实现蝶形运算
{
le = (int)Math.Pow(2, L);
B = le >> 1;
pi = 3.14159f;
for (j = 0; j <= B - 1; j++)
{
p = Math.Pow(2, m - L) * j;
ps = 2 * pi / N * p;
w.real = Math.Cos(ps);
w.imag = -Math.Sin(ps);
for (i = j; i <= N - 1; i = i + le)
{
ip = i + B;
t = EE(xin[ip], w);
xin[ip].real = xin[i].real - t.real;
xin[ip].imag = xin[i].imag - t.imag;
xin[i].real = xin[i].real + t.real;
xin[i].imag = xin[i].imag + t.imag;
}
}
}
}
