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Calculate imaginary part correctly.
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c975145914
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@ -112,7 +112,7 @@ static void calculate_fft(const float *data, complex double *butterfly_buf, size
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// We only have real data.
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// We only have real data.
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for (unsigned i = 1; i < samples / 2; i++)
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for (unsigned i = 1; i < samples / 2; i++)
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butterfly_buf[i] += butterfly_buf[samples - i];
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butterfly_buf[i] += conj(butterfly_buf[samples - i]);
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// Normalize amplitudes.
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// Normalize amplitudes.
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for (unsigned i = 0; i < samples / 2; i++)
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for (unsigned i = 0; i < samples / 2; i++)
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@ -125,23 +125,29 @@ static void test_fft(void)
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float signal[32];
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float signal[32];
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complex double butterfly_buf[16];
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complex double butterfly_buf[16];
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const float freqs[] = {
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const float cos_freqs[] = {
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1.0, 4.0, 6.0,
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1.0, 4.0, 6.0,
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};
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};
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const float sin_freqs[] = {
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-2.0, 5.0, 7.0,
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};
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for (unsigned i = 0; i < 16; i++)
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for (unsigned i = 0; i < 16; i++)
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{
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{
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signal[2 * i] = 0.0;
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signal[2 * i] = 0.0;
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for (unsigned j = 0; j < sizeof(freqs) / sizeof(freqs[0]); j++)
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for (unsigned j = 0; j < sizeof(cos_freqs) / sizeof(cos_freqs[0]); j++)
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signal[2 * i] += cos(2.0 * M_PI * i * freqs[j] / 16.0);
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signal[2 * i] += cos(2.0 * M_PI * i * cos_freqs[j] / 16.0);
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for (unsigned j = 0; j < sizeof(sin_freqs) / sizeof(sin_freqs[0]); j++)
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signal[2 * i] += sin(2.0 * M_PI * i * sin_freqs[j] / 16.0);
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}
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}
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calculate_fft(signal, butterfly_buf, 16);
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calculate_fft(signal, butterfly_buf, 16);
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printf("FFT: { ");
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printf("FFT: { ");
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for (unsigned i = 0; i < 7; i++)
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for (unsigned i = 0; i < 7; i++)
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printf("%4.2lf, ", cabs(butterfly_buf[i]));
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printf("(%4.2lf, %4.2lf), ", creal(butterfly_buf[i]), cimag(butterfly_buf[i]));
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printf("%4.2lf }\n", cabs(butterfly_buf[7]));
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printf("(%4.2lf, %4.2lf) }\n", creal(butterfly_buf[7]), cimag(butterfly_buf[7]));
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}
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}
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// This doesn't yet take account for slight phase distortions,
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// This doesn't yet take account for slight phase distortions,
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