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SPDX License Identifiers are a more compact / standardized way of representing file license information. See: https://spdx.dev/resources/use/#identifiers This was done with the `ambr` search and replace tool. ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
58 lines
1.7 KiB
C++
58 lines
1.7 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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#include "AudioAlgorithms.h"
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#include <AK/Complex.h>
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#include <math.h>
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// This function uses the input vector as output too. therefore, if you wish to
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// leave it intact, pass a copy to this function
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//
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// The sampling frequency must be more than twice the frequency to resolve.
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// The sample window must be at least large enough to reflect the periodicity
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// of the smallest frequency to be resolved.
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//
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// For example, to resolve a 10 KHz and a 2 Hz sine waves we need at least
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// a samplerate of 20 KHz and a window of 0.5 seconds
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//
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// If invert is true, this function computes the inverse discrete fourier transform.
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//
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// The data vector must be a power of 2
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// Adapted from https://cp-algorithms.com/algebra/fft.html
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void fft(Vector<Complex<double>>& sample_data, bool invert)
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{
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int n = sample_data.size();
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auto data = sample_data.data();
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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(data[i], 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 * M_PI / len * (invert ? -1 : 1);
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Complex<double> wlen(cos(ang), 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 = data[i + j], v = data[i + j + len / 2] * w;
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data[i + j] = u + v;
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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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data[i] /= n;
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}
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}
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