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/*
* Copyright (c) 2021, Arne Elster <arne@elster.li>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Array.h>
#include <AK/Math.h>
#include <AK/Span.h>
namespace LibDSP {
template<size_t N>
requires(N % 2 == 0) class MDCT {
public:
constexpr MDCT()
{
for (size_t n = 0; n < N; n++) {
for (size_t k = 0; k < N / 2; k++) {
m_phi[n][k] = AK::cos(AK::Pi<double> / (2 * N) * (2 * n + 1 + N / 2.0) * (2 * k + 1));
}
}
}
void transform(Span<double const> data, Span<double> output)
{
assert(N == 2 * data.size());
assert(N == output.size());
for (size_t n = 0; n < N; n++) {
output[n] = 0;
for (size_t k = 0; k < N / 2; k++) {
output[n] += data[k] * m_phi[n][k];
}
}
}
private:
Array<Array<double, N / 2>, N> m_phi;
};
}
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