comb.hpp

// Comb filter class declaration
//
// Written by Jezar at Dreampoint, June 2000
// http://www.dreampoint.co.uk
// This code is public domain
 
/*
 * Copyright © 2015-2023 Synthstrom Audible Limited
 *
 * This file is part of The Synthstrom Audible Deluge Firmware.
 *
 * The Synthstrom Audible Deluge Firmware 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 with this program.
 * If not, see <https://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include "util/fixedpoint.h"
#include <cstdint>
#include <limits>
#include <span>
 
namespace freeverb {
class Comb {
public:
    Comb() = default;
    constexpr void setBuffer(std::span<int32_t> buffer) { buffer_ = buffer; }
 
    constexpr void mute() { std::fill(buffer_.begin(), buffer_.end(), 0); }
 
    constexpr void setDamp(float val) {
        damp1_ = val * std::numeric_limits<int32_t>::max();
        damp2_ = std::numeric_limits<int32_t>::max() - damp1_;
    }
 
    [[nodiscard]] constexpr float getDamp() const { return damp1_ / std::numeric_limits<int32_t>::max(); }
 
    constexpr void setFeedback(int32_t val) { feedback_ = val; }
 
    [[nodiscard]] constexpr int32_t getFeedback() const { return feedback_; }
 
    // Big to inline - but crucial for speed
    inline int32_t process(int32_t input) {
        int32_t output = buffer_[bufidx_];
 
        filterstore_ = (multiply_32x32_rshift32_rounded(output, damp2_) + //<
                        multiply_32x32_rshift32_rounded(filterstore_, damp1_))
                       << 1;
 
        buffer_[bufidx_] = input + (multiply_32x32_rshift32_rounded(filterstore_, feedback_) << 1);
 
        if (++bufidx_ >= buffer_.size()) {
            bufidx_ = 0;
        }
 
        return output;
    }
 
private:
    int32_t feedback_;
    int32_t filterstore_{0};
    int32_t damp1_;
    int32_t damp2_;
    std::span<int32_t> buffer_;
    int32_t bufidx_{0};
};
} // namespace freeverb
// ends