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https://github.com/RGBCube/serenity
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00dd8f8fbe
Several related improvements to our Fast Fourier Transform implementation: - FFT now operates on spans, allowing it to use many more container types other than Vector. It's intended anyways that FFT transmutes the input data. - FFT is now constexpr, moving the implementation to the header and removing the cpp file. This means that if we have static collections of samples, we can transform them at compile time. - sample_data.data() weirdness is now gone.
49 lines
1.2 KiB
C++
49 lines
1.2 KiB
C++
/*
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* Copyright (c) 2021, Cesar Torres <shortanemoia@protonmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Complex.h>
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#include <AK/Math.h>
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#include <AK/Span.h>
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namespace LibDSP {
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constexpr void fft(Span<Complex<double>> sample_data, bool invert = false)
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{
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int n = sample_data.size();
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for (int i = 1, j = 0; i < n; i++) {
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int bit = n >> 1;
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for (; j & bit; bit >>= 1)
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j ^= bit;
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j ^= bit;
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if (i < j)
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swap(sample_data[i], sample_data[j]);
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}
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for (int len = 2; len <= n; len <<= 1) {
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double ang = 2 * AK::Pi<double> / len * (invert ? -1 : 1);
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Complex<double> wlen(AK::cos(ang), AK::sin(ang));
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for (int i = 0; i < n; i += len) {
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Complex<double> w = { 1., 0. };
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for (int j = 0; j < len / 2; j++) {
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Complex<double> u = sample_data[i + j], v = sample_data[i + j + len / 2] * w;
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sample_data[i + j] = u + v;
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sample_data[i + j + len / 2] = u - v;
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w *= wlen;
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}
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}
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}
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if (invert) {
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for (int i = 0; i < n; i++)
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sample_data[i] /= n;
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}
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}
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}
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