filt_tables.h

/*
 * This file is part of libsidplayfp, a SID player engine.
 *
 *  Copyright (C) 2025-2026 Leandro Nini
 *
 *  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
 */
 
 
// Based on cRSID lightweight RealSID by Hermit (Mihaly Horvath)
 
#include <array>
#include <cstddef>
 
constexpr int ResLength = 0x10;
using res_array_t = std::array<unsigned short, ResLength>;
 
#if __cplusplus > 202302L // std::exp2 is constexpr since c++26
#  include <cmath>
 
    constexpr int CRSID_FILTERTABLE_RESOLUTION = 12;
    constexpr int Magnitude = (1 << CRSID_FILTERTABLE_RESOLUTION);
 
    //8580 Resonance-DAC (1/Q) curve
    constexpr auto createRes8580()
    {
        res_array_t arr {};
 
        for (int i=0; i<ResLength; i++)
        {
            arr[i] = (std::exp2((4 - i) / 8.0)) * Magnitude;
        }
 
        return arr;
    }
 
    //6581 Resonance-DAC (1/Q) curve
    constexpr auto createRes6581()
    {
        res_array_t arr {};
 
        for (int i=0; i<ResLength; i++)
        {
            arr[i] = (i>5 ? 8.0 / i : 1.41) * Magnitude;
        }
 
        return arr;
    }
 
    static constexpr auto Resonances8580 = createRes8580();
    static constexpr auto Resonances6581 = createRes6581();
#else
 
    // 8580 Resonance-DAC (1/Q) curve: Magnitude:$1000
    static const res_array_t Resonances8580 =
    {
        //  0     1      2      3      4      5      6      7      8      9      A      B      C      D      E      F
        0x16A0,0x14BF,0x1306,0x1172,0x1000,0x0EAC,0x0D74,0x0C56,0x0B50,0x0A5F,0x0983,0x08B9,0x0800,0x0756,0x06BA,0x062B,
        //0xFF,  0xFE,  0xFC,  0xF8,  0xF0,  0xE8,  0xD5,  0xC5,  0xB3,  0xA4,  0x97,  0x8A,  0x80,  0x77,  0x6E,  0x66 <- calculated then refined manually to sound best
    };
 
    // 6581 Resonance-DAC (1/Q) curve: Magnitude:$1000
    static const res_array_t Resonances6581 =
    {
        //  0     1      2      3      4      5      6      7      8      9      A      B      C      D      E      F
        0x168F,0x168F,0x168F,0x168F,0x168F,0x168F,0x1555,0x1249,0x1000,0x0E38,0x0CCC,0x0BA2,0x0AAA,0x09D8,0x0924,0x0888,
        //0xFF,  0xFE,  0xFD,  0xFC,  0xFB,  0xF9,  0xF6,  0xF2,  0xEC,  0xE4,  0xCD,  0xBA,  0xAB,  0x9E,  0x92,  0x86 <- calculated then refined manually to sound best
    };
 
#endif