58 lines
1.6 KiB
C
58 lines
1.6 KiB
C
#include <math.h>
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#include <complex.h>
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#include <stdint.h>
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#include <stdlib.h>
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complex float* fft(complex float* p, uint32_t N) {
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complex float w = cexpf(-2 * I * M_PI / N);
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if (N == 1)
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return p;
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complex float* pe = (complex float*)malloc(sizeof(complex float) * (N / 2));
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complex float* po = (complex float*)malloc(sizeof(complex float) * (N / 2));
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for (int i = 0; i < N - 1; i += 2) {
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pe[i / 2] = p[i];
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po[i / 2] = p[i + 1];
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}
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complex float* xe = fft(pe, N / 2);
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complex float* xo = fft(po, N / 2);
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complex float* ps = (complex float*)malloc(sizeof(complex float) * N);
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for (int i = 0; i < N / 2; i++) {
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ps[i] = xe[i] + cpowf(w, (complex float)i) * xo[i];
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ps[i + N / 2] = xe[i] - cpowf(w, (complex float)i) * xo[i];
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}
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return ps;
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}
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complex float* ifft(complex float* p, uint32_t N) {
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complex float w = ((complex float)1 / N) * cexpf(2 * I * M_PI / N);
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if (N == 1)
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return p;
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complex float* pe = (complex float*)malloc(sizeof(complex float) * (N / 2));
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complex float* po = (complex float*)malloc(sizeof(complex float) * (N / 2));
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for (int i = 0; i < N - 1; i += 2) {
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pe[i / 2] = p[i];
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po[i / 2] = p[i + 1];
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}
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complex float* xe = fft(pe, N / 2);
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complex float* xo = fft(po, N / 2);
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complex float* ps = (complex float*)malloc(sizeof(complex float) * N);
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for (int i = 0; i < N / 2; i++) {
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ps[i] = xe[i] + cpowf(w, (complex float)i) * xo[i];
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ps[i + N / 2] = xe[i] - cpowf(w, (complex float)i) * xo[i];
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}
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return ps;
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}
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