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)
{
    const int32_t Vi = input << 11;
    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