flat_top.hpp

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/*
 * eDSP, A cross-platform Digital Signal Processing library written in modern C++.
 * Copyright (C) 2018 Mohammed Boujemaoui Boulaghmoudi, All rights reserved.
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of  MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along width
 * this program.  If not, see <http://www.gnu.org/licenses/>
 *
 * File: flat_top.hpp
 * Author: Mohammed Boujemaoui
 * Date: 27/7/2018
 */
#ifndef EDSP_FLAT_TOP_HPP
#define EDSP_FLAT_TOP_HPP

#include <edsp/math/numeric.hpp>
#include <edsp/math/constant.hpp>
#include <edsp/meta/iterator.hpp>

namespace edsp { namespace windowing {

    template <typename OutputIt>
    constexpr void flattop(OutputIt first, OutputIt last) {
        using value_type  = meta::value_type_t<OutputIt>;
        using size_type   = meta::diff_type_t<OutputIt>;
        constexpr auto a0 = static_cast<value_type>(0.21557895);
        constexpr auto a1 = static_cast<value_type>(0.41663158);
        constexpr auto a2 = static_cast<value_type>(0.277263158);
        constexpr auto a3 = static_cast<value_type>(0.083578947);
        constexpr auto a4 = static_cast<value_type>(0.006947368);
        const auto size   = static_cast<size_type>(std::distance(first, last));
        const auto factor = constants<value_type>::two_pi / static_cast<value_type>(size - 1);
        for (size_type i = 0; i < size; ++i, ++first) {
            const value_type tmp = factor * i;
            *first = a0 - a1 * std::cos(tmp) + a2 * std::cos(2 * tmp) - a3 * std::cos(3 * tmp) + a4 * std::cos(4 * tmp);
        }
    }

}} // namespace edsp::windowing

#endif // EDSP_FLAT_TOP_HPP