a single-file fast fourier transform library (suitable for power of 2 and non-power of 2)
#ifndef STB_FFT_IMPLEMENTAION
#define STB_FFT_IMPLEMENTAION
#endif
#include "stb_fft.h"
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#ifndef max
#define max(a, b) ((a) > (b) ? (a) : (b))
#endif
void fftResample(float *input, float *output, int input_size, int output_size) {
cmplx *samples = (cmplx *) calloc(max(input_size, output_size), sizeof(cmplx));
if (samples == NULL) {
return;
}
STB_FFT_R2C(input, samples, input_size);
if (output_size < input_size) {
// remove some high frequency samples;
int half_output = (output_size / 2);
int diff_size = input_size - output_size;
memset(samples + half_output, 0, diff_size * sizeof(cmplx));
} else if (output_size > input_size) {
int half_input = input_size / 2;
// add some high frequency zero samples
int diff_size = output_size - input_size;
memmove(samples + half_input + diff_size, samples + half_input, half_input * sizeof(cmplx));
memset(samples + half_input, 0, diff_size * sizeof(cmplx));
}
STB_IFFT_C2R(samples, output, output_size);
float norm = 1.0f / input_size;
for (int i = 0; i < output_size; i++) {
output[i] = output[i] * norm;
}
free(samples);
}
int main() {
printf("a single-file fast fourier transform library.\n");
printf("blog: http://cpuimage.cnblogs.com/\n");
const int inSize = 4;
const int outSize = 8;
float input[inSize];
float output[outSize];
printf("\ninput :\n");
for (int i = 0; i < inSize; ++i) {
input[i] = i;
printf("%f \t", input[i]);
}
fftResample(input, output, inSize, outSize);
printf("\noutput :\n");
for (int i = 0; i < outSize; ++i) {
printf("%f \t", output[i]);
}
printf("\npress any key to exit. \n");
getchar();
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