ExternalFilter.h

/*
 * This file is part of libsidplayfp, a SID player engine.
 *
 * Copyright 2011-2025 Leandro Nini <drfiemost@users.sourceforge.net>
 * Copyright 2007-2010 Antti Lankila
 * Copyright 2004 Dag Lem <resid@nimrod.no>
 *
 * 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 2 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

#ifndef EXTERNALFILTER_H
#define EXTERNALFILTER_H

#include "siddefs-fp.h"

#include <cstdint>

namespace reSIDfp
{

class ExternalFilter
{
    friend class State;

private:
    int32_t Vlp;

    int32_t Vhp;

    int32_t w0lp_1_s7 = 0;

    int32_t w0hp_1_s17 = 0;

    double m_frequency;

    double m_ext_res = 10e3;

private:
    void recalcParams();

public:
    int32_t clock(int32_t input);

    ExternalFilter();

    void setClockFrequency(double frequency);

    void setExtResistance(double res);

    void reset();
};

} // namespace reSIDfp

#if RESIDFP_INLINING || defined(EXTERNALFILTER_CPP)

namespace reSIDfp
{

RESIDFP_INLINE
int32_t ExternalFilter::clock(int32_t input)
{
#if __cplusplus >= 202002L
    const int32_t Vi = input << 11;
#else
    // Left shift of negative values is undefined
    const int32_t Vi = input * (1 << 11);
#endif
    const int32_t dVlp = (w0lp_1_s7 * (Vi - Vlp)) >> 7;
    const int32_t dVhp = (w0hp_1_s17 * (Vlp - Vhp)) >> 17;
    Vlp += dVlp;
    Vhp += dVhp;
    return (Vlp - Vhp) >> 11;
}

} // namespace reSIDfp

#endif

#endif