fft的c++实现
代码实现
| #include“fft.h“ | |
| extern complex x[N * 2], *W; | |
| void add(complex a, complex b, complex *c) // 复数加运算 | |
| { | |
| c->real = a.real + b.real; | |
| c->img = a.img + b.img; | |
| } | |
| void sub(complex a, complex b, complex *c) // 复数减运算 | |
| { | |
| c->real = a.real – b.real; | |
| c->img = a.img – b.img; | |
| } | |
| void mul(complex a, complex b, complex *c) // 复数乘运算 | |
| { | |
| c->real = a.real*b.real – a.img*b.img; | |
| c->img = a.real*b.img + a.img*b.real; | |
| } | |
| void divi(complex a, complex b, complex *c) // 复数除运算 | |
| { | |
| c->real = (a.real*b.real + a.img*b.img) / (b.real*b.real + b.img*b.img); | |
| c->img = (a.img*b.real – a.real*b.img) / (b.real*b.real + b.img*b.img); | |
| } | |
| /********************** | |
| @ 欧拉公式运算 | |
| ***********************/ | |
| void initW(int size) | |
| { | |
| int i; | |
| W = (complex*)malloc(sizeof(complex)* size); //分配内存空间 | |
| for (i = 0; i<size; i++) | |
| { | |
| W[i].real = cos(2 * PI / size*i); | |
| W[i].img = –1 * sin(2 * PI / size*i); | |
| } | |
| } | |
| /********************** | |
| @ 变址运算 | |
| ***********************/ | |
| void changex(int size) | |
| { | |
| complex temp; | |
| unsigned int i = 0, j = 0, k = 0; | |
| double t; | |
| for (i = 0; i<size; i++) | |
| { | |
| k = i; j = 0; | |
| t = (log(size) / log(2)); | |
| while ((t–)>0) | |
| { | |
| j = j << 1; | |
| j |= (k & 1); | |
| k = k >> 1; | |
| } | |
| if (j>i) | |
| { | |
| temp = x[i]; | |
| x[i] = x[j]; | |
| x[j] = temp; | |
| } | |
| } | |
| } | |
| /********************** | |
| @ 快速傅里叶函数 | |
| ***********************/ | |
| void fftx() | |
| { | |
| long int i = 0, j = 0, k = 0, l = 0; | |
| complex up, down, product; | |
| changex(N); | |
| for (i = 0; i<log(N) / log(2); i++) /*一级蝶形运算*/ | |
| { | |
| l = 1 << i; | |
| for (j = 0; j<N; j += 2 * l) /*一组蝶形运算*/ | |
| { | |
| for (k = 0; k<l; k++) /*一个蝶形运算*/ | |
| { | |
| mul(x[j + k + l], W[N*k / 2 / l], &product); | |
| add(x[j + k], product, &up); | |
| sub(x[j + k], product, &down); | |
| x[j + k] = up; | |
| x[j + k + l] = down; | |
| } | |
| } | |
| } | |
| } | |
| /********************** | |
| @ 输出x结果 | |
| ***********************/ | |
| void output() | |
| { | |
| int i; | |
| printf(“\nx傅里叶变换结果\n“); | |
| for (i = 0; i<N; i++) | |
| { | |
| if (i % 4 == 0 && i != 0) printf(“\n“); | |
| printf(” %.2f“, x[i].real); | |
| if (x[i].img >= 0.0001) | |
| printf(“+%.2fj “, x[i].img); | |
| else if (fabs(x[i].img)<0.0001) | |
| printf(“+0.0000j “); | |
| else | |
| printf(“%.2fj “, x[i].img); | |
| } | |
| printf(“\n“); | |
| } |
参考网址：https://github.com/DUTFangXiang/FFT
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