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cd21e03225
Calculating sin and cos at once is quite a bit cheaper than calculating them individually. x87 has even a dedicated instruction for it: `fsincos`.
50 lines
1.2 KiB
C++
50 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 = Complex<double>::from_polar(1., 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];
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Complex<double> 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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