有没有fft算法的c语言代码

是的，FFT算法的C语言代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define PI 3.14159265358979323846

typedef struct {
    double real;
    double imag;
} complex;

complex* fft(complex* x, int n) {
    if (n == 1) {
        return x;
    }
    complex* xe = (complex*) malloc(n / 2 * sizeof(complex));
    complex* xo = (complex*) malloc(n / 2 * sizeof(complex));
    for (int i = 0; i < n / 2; i++) {
        xe[i] = x[2 * i];
        xo[i] = x[2 * i + 1];
    }
    complex* ye = fft(xe, n / 2);
    complex* yo = fft(xo, n / 2);
    complex* y = (complex*) malloc(n * sizeof(complex));
    for (int k = 0; k < n / 2; k++) {
        double theta = -2 * k * PI / n;
        complex w = {cos(theta), sin(theta)};
        y[k] = {ye[k].real + w.real * yo[k].real - w.imag * yo[k].imag,
                ye[k].imag + w.real * yo[k].imag + w.imag * yo[k].real};
        y[k + n / 2] = {ye[k].real - w.real * yo[k].real + w.imag * yo[k].imag,
                        ye[k].imag - w.real * yo[k].imag - w.imag * yo[k].real};
    }
    free(xe);
    free(xo);
    free(ye);
    free(yo);
    return y;
}

int main() {
    int n = 8;
    complex x[] = {{1, 0}, {2, 0}, {3, 0}, {4, 0}, {4, 0}, {3, 0}, {2, 0}, {1, 0}};
    complex* y = fft(x, n);
    for (int i = 0; i < n; i++) {
        printf("(%g, %g)\n", y[i].real, y[i].imag);
    }
    free(y);
    return 0;
}

这是一个简单的FFT算法实现，输入一个长度为2^k的复数序列，输出其DFT（离散傅里叶变换）。代码中使用递归实现FFT算法，使用了复数运算。