opl3.c

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/* Nuked OPL3
 * Copyright (C) 2013-2020 Nuke.YKT
 *
 * This file is part of Nuked OPL3.
 *
 * Nuked OPL3 is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1
 * of the License, or (at your option) any later version.
 *
 * Nuked OPL3 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with Nuked OPL3. If not, see <https://www.gnu.org/licenses/>.
 
 *  Nuked OPL3 emulator.
 *  Thanks:
 *      MAME Development Team(Jarek Burczynski, Tatsuyuki Satoh):
 *          Feedback and Rhythm part calculation information.
 *      forums.submarine.org.uk(carbon14, opl3):
 *          Tremolo and phase generator calculation information.
 *      OPLx decapsulated(Matthew Gambrell, Olli Niemitalo):
 *          OPL2 ROMs.
 *      siliconpr0n.org(John McMaster, digshadow):
 *          YMF262 and VRC VII decaps and die shots.
 *
 * version: 1.8
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "xemu/opl3.h"
 
#define RSM_FRAC    10
 
// Channel types
 
enum {
    ch_2op = 0,
    ch_4op = 1,
    ch_4op2 = 2,
    ch_drum = 3
};
 
// Envelope key types
 
enum {
    egk_norm = 0x01,
    egk_drum = 0x02
};
 
 
//
// logsin table
//
 
static const uint16_t logsinrom[256] = {
    0x859, 0x6c3, 0x607, 0x58b, 0x52e, 0x4e4, 0x4a6, 0x471,
    0x443, 0x41a, 0x3f5, 0x3d3, 0x3b5, 0x398, 0x37e, 0x365,
    0x34e, 0x339, 0x324, 0x311, 0x2ff, 0x2ed, 0x2dc, 0x2cd,
    0x2bd, 0x2af, 0x2a0, 0x293, 0x286, 0x279, 0x26d, 0x261,
    0x256, 0x24b, 0x240, 0x236, 0x22c, 0x222, 0x218, 0x20f,
    0x206, 0x1fd, 0x1f5, 0x1ec, 0x1e4, 0x1dc, 0x1d4, 0x1cd,
    0x1c5, 0x1be, 0x1b7, 0x1b0, 0x1a9, 0x1a2, 0x19b, 0x195,
    0x18f, 0x188, 0x182, 0x17c, 0x177, 0x171, 0x16b, 0x166,
    0x160, 0x15b, 0x155, 0x150, 0x14b, 0x146, 0x141, 0x13c,
    0x137, 0x133, 0x12e, 0x129, 0x125, 0x121, 0x11c, 0x118,
    0x114, 0x10f, 0x10b, 0x107, 0x103, 0x0ff, 0x0fb, 0x0f8,
    0x0f4, 0x0f0, 0x0ec, 0x0e9, 0x0e5, 0x0e2, 0x0de, 0x0db,
    0x0d7, 0x0d4, 0x0d1, 0x0cd, 0x0ca, 0x0c7, 0x0c4, 0x0c1,
    0x0be, 0x0bb, 0x0b8, 0x0b5, 0x0b2, 0x0af, 0x0ac, 0x0a9,
    0x0a7, 0x0a4, 0x0a1, 0x09f, 0x09c, 0x099, 0x097, 0x094,
    0x092, 0x08f, 0x08d, 0x08a, 0x088, 0x086, 0x083, 0x081,
    0x07f, 0x07d, 0x07a, 0x078, 0x076, 0x074, 0x072, 0x070,
    0x06e, 0x06c, 0x06a, 0x068, 0x066, 0x064, 0x062, 0x060,
    0x05e, 0x05c, 0x05b, 0x059, 0x057, 0x055, 0x053, 0x052,
    0x050, 0x04e, 0x04d, 0x04b, 0x04a, 0x048, 0x046, 0x045,
    0x043, 0x042, 0x040, 0x03f, 0x03e, 0x03c, 0x03b, 0x039,
    0x038, 0x037, 0x035, 0x034, 0x033, 0x031, 0x030, 0x02f,
    0x02e, 0x02d, 0x02b, 0x02a, 0x029, 0x028, 0x027, 0x026,
    0x025, 0x024, 0x023, 0x022, 0x021, 0x020, 0x01f, 0x01e,
    0x01d, 0x01c, 0x01b, 0x01a, 0x019, 0x018, 0x017, 0x017,
    0x016, 0x015, 0x014, 0x014, 0x013, 0x012, 0x011, 0x011,
    0x010, 0x00f, 0x00f, 0x00e, 0x00d, 0x00d, 0x00c, 0x00c,
    0x00b, 0x00a, 0x00a, 0x009, 0x009, 0x008, 0x008, 0x007,
    0x007, 0x007, 0x006, 0x006, 0x005, 0x005, 0x005, 0x004,
    0x004, 0x004, 0x003, 0x003, 0x003, 0x002, 0x002, 0x002,
    0x002, 0x001, 0x001, 0x001, 0x001, 0x001, 0x001, 0x001,
    0x000, 0x000, 0x000, 0x000, 0x000, 0x000, 0x000, 0x000
};
 
//
// exp table
//
 
static const uint16_t exprom[256] = {
    0x7fa, 0x7f5, 0x7ef, 0x7ea, 0x7e4, 0x7df, 0x7da, 0x7d4,
    0x7cf, 0x7c9, 0x7c4, 0x7bf, 0x7b9, 0x7b4, 0x7ae, 0x7a9,
    0x7a4, 0x79f, 0x799, 0x794, 0x78f, 0x78a, 0x784, 0x77f,
    0x77a, 0x775, 0x770, 0x76a, 0x765, 0x760, 0x75b, 0x756,
    0x751, 0x74c, 0x747, 0x742, 0x73d, 0x738, 0x733, 0x72e,
    0x729, 0x724, 0x71f, 0x71a, 0x715, 0x710, 0x70b, 0x706,
    0x702, 0x6fd, 0x6f8, 0x6f3, 0x6ee, 0x6e9, 0x6e5, 0x6e0,
    0x6db, 0x6d6, 0x6d2, 0x6cd, 0x6c8, 0x6c4, 0x6bf, 0x6ba,
    0x6b5, 0x6b1, 0x6ac, 0x6a8, 0x6a3, 0x69e, 0x69a, 0x695,
    0x691, 0x68c, 0x688, 0x683, 0x67f, 0x67a, 0x676, 0x671,
    0x66d, 0x668, 0x664, 0x65f, 0x65b, 0x657, 0x652, 0x64e,
    0x649, 0x645, 0x641, 0x63c, 0x638, 0x634, 0x630, 0x62b,
    0x627, 0x623, 0x61e, 0x61a, 0x616, 0x612, 0x60e, 0x609,
    0x605, 0x601, 0x5fd, 0x5f9, 0x5f5, 0x5f0, 0x5ec, 0x5e8,
    0x5e4, 0x5e0, 0x5dc, 0x5d8, 0x5d4, 0x5d0, 0x5cc, 0x5c8,
    0x5c4, 0x5c0, 0x5bc, 0x5b8, 0x5b4, 0x5b0, 0x5ac, 0x5a8,
    0x5a4, 0x5a0, 0x59c, 0x599, 0x595, 0x591, 0x58d, 0x589,
    0x585, 0x581, 0x57e, 0x57a, 0x576, 0x572, 0x56f, 0x56b,
    0x567, 0x563, 0x560, 0x55c, 0x558, 0x554, 0x551, 0x54d,
    0x549, 0x546, 0x542, 0x53e, 0x53b, 0x537, 0x534, 0x530,
    0x52c, 0x529, 0x525, 0x522, 0x51e, 0x51b, 0x517, 0x514,
    0x510, 0x50c, 0x509, 0x506, 0x502, 0x4ff, 0x4fb, 0x4f8,
    0x4f4, 0x4f1, 0x4ed, 0x4ea, 0x4e7, 0x4e3, 0x4e0, 0x4dc,
    0x4d9, 0x4d6, 0x4d2, 0x4cf, 0x4cc, 0x4c8, 0x4c5, 0x4c2,
    0x4be, 0x4bb, 0x4b8, 0x4b5, 0x4b1, 0x4ae, 0x4ab, 0x4a8,
    0x4a4, 0x4a1, 0x49e, 0x49b, 0x498, 0x494, 0x491, 0x48e,
    0x48b, 0x488, 0x485, 0x482, 0x47e, 0x47b, 0x478, 0x475,
    0x472, 0x46f, 0x46c, 0x469, 0x466, 0x463, 0x460, 0x45d,
    0x45a, 0x457, 0x454, 0x451, 0x44e, 0x44b, 0x448, 0x445,
    0x442, 0x43f, 0x43c, 0x439, 0x436, 0x433, 0x430, 0x42d,
    0x42a, 0x428, 0x425, 0x422, 0x41f, 0x41c, 0x419, 0x416,
    0x414, 0x411, 0x40e, 0x40b, 0x408, 0x406, 0x403, 0x400
};
 
//
// freq mult table multiplied by 2
//
// 1/2, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 12, 12, 15, 15
//
 
static const uint8_t mt[16] = {
    1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 20, 24, 24, 30, 30
};
 
//
// ksl table
//
 
static const uint8_t kslrom[16] = {
    0, 32, 40, 45, 48, 51, 53, 55, 56, 58, 59, 60, 61, 62, 63, 64
};
 
static const uint8_t kslshift[4] = {
    8, 1, 2, 0
};
 
//
// envelope generator constants
//
 
static const uint8_t eg_incstep[4][4] = {
    { 0, 0, 0, 0 },
    { 1, 0, 0, 0 },
    { 1, 0, 1, 0 },
    { 1, 1, 1, 0 }
};
 
//
// address decoding
//
 
static const int8_t ad_slot[0x20] = {
    0, 1, 2, 3, 4, 5, -1, -1, 6, 7, 8, 9, 10, 11, -1, -1,
    12, 13, 14, 15, 16, 17, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
};
 
static const uint8_t ch_slot[18] = {
    0, 1, 2, 6, 7, 8, 12, 13, 14, 18, 19, 20, 24, 25, 26, 30, 31, 32
};
 
//
// Envelope generator
//
 
typedef int16_t(*envelope_sinfunc)(uint16_t phase, uint16_t envelope);
typedef void(*envelope_genfunc)(opl3_slot *slott);
 
static int16_t OPL3_EnvelopeCalcExp(uint32_t level)
{
    if (level > 0x1fff)
    {
        level = 0x1fff;
    }
    return (exprom[level & 0xff] << 1) >> (level >> 8);
}
 
static int16_t OPL3_EnvelopeCalcSin0(uint16_t phase, uint16_t envelope)
{
    uint16_t out = 0;
    uint16_t neg = 0;
    phase &= 0x3ff;
    if (phase & 0x200)
    {
        neg = 0xffff;
    }
    if (phase & 0x100)
    {
        out = logsinrom[(phase & 0xff) ^ 0xff];
    }
    else
    {
        out = logsinrom[phase & 0xff];
    }
    return OPL3_EnvelopeCalcExp(out + (envelope << 3)) ^ neg;
}
 
static int16_t OPL3_EnvelopeCalcSin1(uint16_t phase, uint16_t envelope)
{
    uint16_t out = 0;
    phase &= 0x3ff;
    if (phase & 0x200)
    {
        out = 0x1000;
    }
    else if (phase & 0x100)
    {
        out = logsinrom[(phase & 0xff) ^ 0xff];
    }
    else
    {
        out = logsinrom[phase & 0xff];
    }
    return OPL3_EnvelopeCalcExp(out + (envelope << 3));
}
 
static int16_t OPL3_EnvelopeCalcSin2(uint16_t phase, uint16_t envelope)
{
    uint16_t out = 0;
    phase &= 0x3ff;
    if (phase & 0x100)
    {
        out = logsinrom[(phase & 0xff) ^ 0xff];
    }
    else
    {
        out = logsinrom[phase & 0xff];
    }
    return OPL3_EnvelopeCalcExp(out + (envelope << 3));
}
 
static int16_t OPL3_EnvelopeCalcSin3(uint16_t phase, uint16_t envelope)
{
    uint16_t out = 0;
    phase &= 0x3ff;
    if (phase & 0x100)
    {
        out = 0x1000;
    }
    else
    {
        out = logsinrom[phase & 0xff];
    }
    return OPL3_EnvelopeCalcExp(out + (envelope << 3));
}
 
static int16_t OPL3_EnvelopeCalcSin4(uint16_t phase, uint16_t envelope)
{
    uint16_t out = 0;
    uint16_t neg = 0;
    phase &= 0x3ff;
    if ((phase & 0x300) == 0x100)
    {
        neg = 0xffff;
    }
    if (phase & 0x200)
    {
        out = 0x1000;
    }
    else if (phase & 0x80)
    {
        out = logsinrom[((phase ^ 0xff) << 1) & 0xff];
    }
    else
    {
        out = logsinrom[(phase << 1) & 0xff];
    }
    return OPL3_EnvelopeCalcExp(out + (envelope << 3)) ^ neg;
}
 
static int16_t OPL3_EnvelopeCalcSin5(uint16_t phase, uint16_t envelope)
{
    uint16_t out = 0;
    phase &= 0x3ff;
    if (phase & 0x200)
    {
        out = 0x1000;
    }
    else if (phase & 0x80)
    {
        out = logsinrom[((phase ^ 0xff) << 1) & 0xff];
    }
    else
    {
        out = logsinrom[(phase << 1) & 0xff];
    }
    return OPL3_EnvelopeCalcExp(out + (envelope << 3));
}
 
static int16_t OPL3_EnvelopeCalcSin6(uint16_t phase, uint16_t envelope)
{
    uint16_t neg = 0;
    phase &= 0x3ff;
    if (phase & 0x200)
    {
        neg = 0xffff;
    }
    return OPL3_EnvelopeCalcExp(envelope << 3) ^ neg;
}
 
static int16_t OPL3_EnvelopeCalcSin7(uint16_t phase, uint16_t envelope)
{
    uint16_t out = 0;
    uint16_t neg = 0;
    phase &= 0x3ff;
    if (phase & 0x200)
    {
        neg = 0xffff;
        phase = (phase & 0x1ff) ^ 0x1ff;
    }
    out = phase << 3;
    return OPL3_EnvelopeCalcExp(out + (envelope << 3)) ^ neg;
}
 
static const envelope_sinfunc envelope_sin[8] = {
    OPL3_EnvelopeCalcSin0,
    OPL3_EnvelopeCalcSin1,
    OPL3_EnvelopeCalcSin2,
    OPL3_EnvelopeCalcSin3,
    OPL3_EnvelopeCalcSin4,
    OPL3_EnvelopeCalcSin5,
    OPL3_EnvelopeCalcSin6,
    OPL3_EnvelopeCalcSin7
};
 
enum envelope_gen_num
{
    envelope_gen_num_attack = 0,
    envelope_gen_num_decay = 1,
    envelope_gen_num_sustain = 2,
    envelope_gen_num_release = 3
};
 
static void OPL3_EnvelopeUpdateKSL(opl3_slot *slot)
{
    int16_t ksl = (kslrom[slot->channel->f_num >> 6] << 2)
               - ((0x08 - slot->channel->block) << 5);
    if (ksl < 0)
    {
        ksl = 0;
    }
    slot->eg_ksl = (uint8_t)ksl;
}
 
static void OPL3_EnvelopeCalc(opl3_slot *slot)
{
    uint8_t nonzero;
    uint8_t rate;
    uint8_t rate_hi;
    uint8_t rate_lo;
    uint8_t reg_rate = 0;
    uint8_t ks;
    uint8_t eg_shift, shift;
    uint16_t eg_rout;
    int16_t eg_inc;
    uint8_t eg_off;
    uint8_t reset = 0;
    slot->eg_out = slot->eg_rout + (slot->reg_tl << 2)
                 + (slot->eg_ksl >> kslshift[slot->reg_ksl]) + *slot->trem;
    if (slot->key && slot->eg_gen == envelope_gen_num_release)
    {
        reset = 1;
        reg_rate = slot->reg_ar;
    }
    else
    {
        switch (slot->eg_gen)
        {
        case envelope_gen_num_attack:
            reg_rate = slot->reg_ar;
            break;
        case envelope_gen_num_decay:
            reg_rate = slot->reg_dr;
            break;
        case envelope_gen_num_sustain:
            if (!slot->reg_type)
            {
                reg_rate = slot->reg_rr;
            }
            break;
        case envelope_gen_num_release:
            reg_rate = slot->reg_rr;
            break;
        }
    }
    slot->pg_reset = reset;
    ks = slot->channel->ksv >> ((slot->reg_ksr ^ 1) << 1);
    nonzero = (reg_rate != 0);
    rate = ks + (reg_rate << 2);
    rate_hi = rate >> 2;
    rate_lo = rate & 0x03;
    if (rate_hi & 0x10)
    {
        rate_hi = 0x0f;
    }
    eg_shift = rate_hi + slot->chip->eg_add;
    shift = 0;
    if (nonzero)
    {
        if (rate_hi < 12)
        {
            if (slot->chip->eg_state)
            {
                switch (eg_shift)
                {
                case 12:
                    shift = 1;
                    break;
                case 13:
                    shift = (rate_lo >> 1) & 0x01;
                    break;
                case 14:
                    shift = rate_lo & 0x01;
                    break;
                default:
                    break;
                }
            }
        }
        else
        {
            shift = (rate_hi & 0x03) + eg_incstep[rate_lo][slot->chip->timer & 0x03];
            if (shift & 0x04)
            {
                shift = 0x03;
            }
            if (!shift)
            {
                shift = slot->chip->eg_state;
            }
        }
    }
    eg_rout = slot->eg_rout;
    eg_inc = 0;
    eg_off = 0;
    // Instant attack
    if (reset && rate_hi == 0x0f)
    {
        eg_rout = 0x00;
    }
    // Envelope off
    if ((slot->eg_rout & 0x1f8) == 0x1f8)
    {
        eg_off = 1;
    }
    if (slot->eg_gen != envelope_gen_num_attack && !reset && eg_off)
    {
        eg_rout = 0x1ff;
    }
    switch (slot->eg_gen)
    {
    case envelope_gen_num_attack:
        if (!slot->eg_rout)
        {
            slot->eg_gen = envelope_gen_num_decay;
        }
        else if (slot->key && shift > 0 && rate_hi != 0x0f)
        {
            eg_inc = ~slot->eg_rout >> (4 - shift);
        }
        break;
    case envelope_gen_num_decay:
        if ((slot->eg_rout >> 4) == slot->reg_sl)
        {
            slot->eg_gen = envelope_gen_num_sustain;
        }
        else if (!eg_off && !reset && shift > 0)
        {
            eg_inc = 1 << (shift - 1);
        }
        break;
    case envelope_gen_num_sustain:
    case envelope_gen_num_release:
        if (!eg_off && !reset && shift > 0)
        {
            eg_inc = 1 << (shift - 1);
        }
        break;
    }
    slot->eg_rout = (eg_rout + eg_inc) & 0x1ff;
    // Key off
    if (reset)
    {
        slot->eg_gen = envelope_gen_num_attack;
    }
    if (!slot->key)
    {
        slot->eg_gen = envelope_gen_num_release;
    }
}
 
static void OPL3_EnvelopeKeyOn(opl3_slot *slot, uint8_t type)
{
    slot->key |= type;
}
 
static void OPL3_EnvelopeKeyOff(opl3_slot *slot, uint8_t type)
{
    slot->key &= ~type;
}
 
//
// Phase Generator
//
 
static void OPL3_PhaseGenerate(opl3_slot *slot)
{
    opl3_chip *chip;
    uint16_t f_num;
    uint32_t basefreq;
    uint8_t rm_xor, n_bit;
    uint32_t noise;
    uint16_t phase;
 
    chip = slot->chip;
    f_num = slot->channel->f_num;
    if (slot->reg_vib)
    {
        int8_t range;
        uint8_t vibpos;
 
        range = (f_num >> 7) & 7;
        vibpos = slot->chip->vibpos;
 
        if (!(vibpos & 3))
        {
            range = 0;
        }
        else if (vibpos & 1)
        {
            range >>= 1;
        }
        range >>= slot->chip->vibshift;
 
        if (vibpos & 4)
        {
            range = -range;
        }
        f_num += range;
    }
    basefreq = (f_num << slot->channel->block) >> 1;
    phase = (uint16_t)(slot->pg_phase >> 9);
    if (slot->pg_reset)
    {
        slot->pg_phase = 0;
    }
    slot->pg_phase += (basefreq * mt[slot->reg_mult]) >> 1;
    // Rhythm mode
    noise = chip->noise;
    slot->pg_phase_out = phase;
    if (slot->slot_num == 13) // hh
    {
        chip->rm_hh_bit2 = (phase >> 2) & 1;
        chip->rm_hh_bit3 = (phase >> 3) & 1;
        chip->rm_hh_bit7 = (phase >> 7) & 1;
        chip->rm_hh_bit8 = (phase >> 8) & 1;
    }
    if (slot->slot_num == 17 && (chip->rhy & 0x20)) // tc
    {
        chip->rm_tc_bit3 = (phase >> 3) & 1;
        chip->rm_tc_bit5 = (phase >> 5) & 1;
    }
    if (chip->rhy & 0x20)
    {
        rm_xor = (chip->rm_hh_bit2 ^ chip->rm_hh_bit7)
               | (chip->rm_hh_bit3 ^ chip->rm_tc_bit5)
               | (chip->rm_tc_bit3 ^ chip->rm_tc_bit5);
        switch (slot->slot_num)
        {
        case 13: // hh
            slot->pg_phase_out = rm_xor << 9;
            if (rm_xor ^ (noise & 1))
            {
                slot->pg_phase_out |= 0xd0;
            }
            else
            {
                slot->pg_phase_out |= 0x34;
            }
            break;
        case 16: // sd
            slot->pg_phase_out = (chip->rm_hh_bit8 << 9)
                               | ((chip->rm_hh_bit8 ^ (noise & 1)) << 8);
            break;
        case 17: // tc
            slot->pg_phase_out = (rm_xor << 9) | 0x80;
            break;
        default:
            break;
        }
    }
    n_bit = ((noise >> 14) ^ noise) & 0x01;
    chip->noise = (noise >> 1) | (n_bit << 22);
}
 
//
// Slot
//
 
static void OPL3_SlotWrite20(opl3_slot *slot, uint8_t data)
{
    if ((data >> 7) & 0x01)
    {
        slot->trem = &slot->chip->tremolo;
    }
    else
    {
        slot->trem = (uint8_t*)&slot->chip->zeromod;
    }
    slot->reg_vib = (data >> 6) & 0x01;
    slot->reg_type = (data >> 5) & 0x01;
    slot->reg_ksr = (data >> 4) & 0x01;
    slot->reg_mult = data & 0x0f;
}
 
static void OPL3_SlotWrite40(opl3_slot *slot, uint8_t data)
{
    slot->reg_ksl = (data >> 6) & 0x03;
    slot->reg_tl = data & 0x3f;
    OPL3_EnvelopeUpdateKSL(slot);
}
 
static void OPL3_SlotWrite60(opl3_slot *slot, uint8_t data)
{
    slot->reg_ar = (data >> 4) & 0x0f;
    slot->reg_dr = data & 0x0f;
}
 
static void OPL3_SlotWrite80(opl3_slot *slot, uint8_t data)
{
    slot->reg_sl = (data >> 4) & 0x0f;
    if (slot->reg_sl == 0x0f)
    {
        slot->reg_sl = 0x1f;
    }
    slot->reg_rr = data & 0x0f;
}
 
static void OPL3_SlotWriteE0(opl3_slot *slot, uint8_t data)
{
    slot->reg_wf = data & 0x07;
    if (slot->chip->newm == 0x00)
    {
        slot->reg_wf &= 0x03;
    }
}
 
static void OPL3_SlotGenerate(opl3_slot *slot)
{
    slot->out = envelope_sin[slot->reg_wf](slot->pg_phase_out + *slot->mod, slot->eg_out);
}
 
static void OPL3_SlotCalcFB(opl3_slot *slot)
{
    if (slot->channel->fb != 0x00)
    {
        slot->fbmod = (slot->prout + slot->out) >> (0x09 - slot->channel->fb);
    }
    else
    {
        slot->fbmod = 0;
    }
    slot->prout = slot->out;
}
 
//
// Channel
//
 
static void OPL3_ChannelSetupAlg(opl3_channel *channel);
 
static void OPL3_ChannelUpdateRhythm(opl3_chip *chip, uint8_t data)
{
    opl3_channel *channel6;
    opl3_channel *channel7;
    opl3_channel *channel8;
    uint8_t chnum;
 
    chip->rhy = data & 0x3f;
    if (chip->rhy & 0x20)
    {
        channel6 = &chip->channel[6];
        channel7 = &chip->channel[7];
        channel8 = &chip->channel[8];
        channel6->out[0] = &channel6->slots[1]->out;
        channel6->out[1] = &channel6->slots[1]->out;
        channel6->out[2] = &chip->zeromod;
        channel6->out[3] = &chip->zeromod;
        channel7->out[0] = &channel7->slots[0]->out;
        channel7->out[1] = &channel7->slots[0]->out;
        channel7->out[2] = &channel7->slots[1]->out;
        channel7->out[3] = &channel7->slots[1]->out;
        channel8->out[0] = &channel8->slots[0]->out;
        channel8->out[1] = &channel8->slots[0]->out;
        channel8->out[2] = &channel8->slots[1]->out;
        channel8->out[3] = &channel8->slots[1]->out;
        for (chnum = 6; chnum < 9; chnum++)
        {
            chip->channel[chnum].chtype = ch_drum;
        }
        OPL3_ChannelSetupAlg(channel6);
        OPL3_ChannelSetupAlg(channel7);
        OPL3_ChannelSetupAlg(channel8);
        //hh
        if (chip->rhy & 0x01)
        {
            OPL3_EnvelopeKeyOn(channel7->slots[0], egk_drum);
        }
        else
        {
            OPL3_EnvelopeKeyOff(channel7->slots[0], egk_drum);
        }
        //tc
        if (chip->rhy & 0x02)
        {
            OPL3_EnvelopeKeyOn(channel8->slots[1], egk_drum);
        }
        else
        {
            OPL3_EnvelopeKeyOff(channel8->slots[1], egk_drum);
        }
        //tom
        if (chip->rhy & 0x04)
        {
            OPL3_EnvelopeKeyOn(channel8->slots[0], egk_drum);
        }
        else
        {
            OPL3_EnvelopeKeyOff(channel8->slots[0], egk_drum);
        }
        //sd
        if (chip->rhy & 0x08)
        {
            OPL3_EnvelopeKeyOn(channel7->slots[1], egk_drum);
        }
        else
        {
            OPL3_EnvelopeKeyOff(channel7->slots[1], egk_drum);
        }
        //bd
        if (chip->rhy & 0x10)
        {
            OPL3_EnvelopeKeyOn(channel6->slots[0], egk_drum);
            OPL3_EnvelopeKeyOn(channel6->slots[1], egk_drum);
        }
        else
        {
            OPL3_EnvelopeKeyOff(channel6->slots[0], egk_drum);
            OPL3_EnvelopeKeyOff(channel6->slots[1], egk_drum);
        }
    }
    else
    {
        for (chnum = 6; chnum < 9; chnum++)
        {
            chip->channel[chnum].chtype = ch_2op;
            OPL3_ChannelSetupAlg(&chip->channel[chnum]);
            OPL3_EnvelopeKeyOff(chip->channel[chnum].slots[0], egk_drum);
            OPL3_EnvelopeKeyOff(chip->channel[chnum].slots[1], egk_drum);
        }
    }
}
 
static void OPL3_ChannelWriteA0(opl3_channel *channel, uint8_t data)
{
    if (channel->chip->newm && channel->chtype == ch_4op2)
    {
        return;
    }
    channel->f_num = (channel->f_num & 0x300) | data;
    channel->ksv = (channel->block << 1)
                 | ((channel->f_num >> (0x09 - channel->chip->nts)) & 0x01);
    OPL3_EnvelopeUpdateKSL(channel->slots[0]);
    OPL3_EnvelopeUpdateKSL(channel->slots[1]);
    if (channel->chip->newm && channel->chtype == ch_4op)
    {
        channel->pair->f_num = channel->f_num;
        channel->pair->ksv = channel->ksv;
        OPL3_EnvelopeUpdateKSL(channel->pair->slots[0]);
        OPL3_EnvelopeUpdateKSL(channel->pair->slots[1]);
    }
}
 
static void OPL3_ChannelWriteB0(opl3_channel *channel, uint8_t data)
{
    if (channel->chip->newm && channel->chtype == ch_4op2)
    {
        return;
    }
    channel->f_num = (channel->f_num & 0xff) | ((data & 0x03) << 8);
    channel->block = (data >> 2) & 0x07;
    channel->ksv = (channel->block << 1)
                 | ((channel->f_num >> (0x09 - channel->chip->nts)) & 0x01);
    OPL3_EnvelopeUpdateKSL(channel->slots[0]);
    OPL3_EnvelopeUpdateKSL(channel->slots[1]);
    if (channel->chip->newm && channel->chtype == ch_4op)
    {
        channel->pair->f_num = channel->f_num;
        channel->pair->block = channel->block;
        channel->pair->ksv = channel->ksv;
        OPL3_EnvelopeUpdateKSL(channel->pair->slots[0]);
        OPL3_EnvelopeUpdateKSL(channel->pair->slots[1]);
    }
}
 
static void OPL3_ChannelSetupAlg(opl3_channel *channel)
{
    if (channel->chtype == ch_drum)
    {
        if (channel->ch_num == 7 || channel->ch_num == 8)
        {
            channel->slots[0]->mod = &channel->chip->zeromod;
            channel->slots[1]->mod = &channel->chip->zeromod;
            return;
        }
        switch (channel->alg & 0x01)
        {
        case 0x00:
            channel->slots[0]->mod = &channel->slots[0]->fbmod;
            channel->slots[1]->mod = &channel->slots[0]->out;
            break;
        case 0x01:
            channel->slots[0]->mod = &channel->slots[0]->fbmod;
            channel->slots[1]->mod = &channel->chip->zeromod;
            break;
        }
        return;
    }
    if (channel->alg & 0x08)
    {
        return;
    }
    if (channel->alg & 0x04)
    {
        channel->pair->out[0] = &channel->chip->zeromod;
        channel->pair->out[1] = &channel->chip->zeromod;
        channel->pair->out[2] = &channel->chip->zeromod;
        channel->pair->out[3] = &channel->chip->zeromod;
        switch (channel->alg & 0x03)
        {
        case 0x00:
            channel->pair->slots[0]->mod = &channel->pair->slots[0]->fbmod;
            channel->pair->slots[1]->mod = &channel->pair->slots[0]->out;
            channel->slots[0]->mod = &channel->pair->slots[1]->out;
            channel->slots[1]->mod = &channel->slots[0]->out;
            channel->out[0] = &channel->slots[1]->out;
            channel->out[1] = &channel->chip->zeromod;
            channel->out[2] = &channel->chip->zeromod;
            channel->out[3] = &channel->chip->zeromod;
            break;
        case 0x01:
            channel->pair->slots[0]->mod = &channel->pair->slots[0]->fbmod;
            channel->pair->slots[1]->mod = &channel->pair->slots[0]->out;
            channel->slots[0]->mod = &channel->chip->zeromod;
            channel->slots[1]->mod = &channel->slots[0]->out;
            channel->out[0] = &channel->pair->slots[1]->out;
            channel->out[1] = &channel->slots[1]->out;
            channel->out[2] = &channel->chip->zeromod;
            channel->out[3] = &channel->chip->zeromod;
            break;
        case 0x02:
            channel->pair->slots[0]->mod = &channel->pair->slots[0]->fbmod;
            channel->pair->slots[1]->mod = &channel->chip->zeromod;
            channel->slots[0]->mod = &channel->pair->slots[1]->out;
            channel->slots[1]->mod = &channel->slots[0]->out;
            channel->out[0] = &channel->pair->slots[0]->out;
            channel->out[1] = &channel->slots[1]->out;
            channel->out[2] = &channel->chip->zeromod;
            channel->out[3] = &channel->chip->zeromod;
            break;
        case 0x03:
            channel->pair->slots[0]->mod = &channel->pair->slots[0]->fbmod;
            channel->pair->slots[1]->mod = &channel->chip->zeromod;
            channel->slots[0]->mod = &channel->pair->slots[1]->out;
            channel->slots[1]->mod = &channel->chip->zeromod;
            channel->out[0] = &channel->pair->slots[0]->out;
            channel->out[1] = &channel->slots[0]->out;
            channel->out[2] = &channel->slots[1]->out;
            channel->out[3] = &channel->chip->zeromod;
            break;
        }
    }
    else
    {
        switch (channel->alg & 0x01)
        {
        case 0x00:
            channel->slots[0]->mod = &channel->slots[0]->fbmod;
            channel->slots[1]->mod = &channel->slots[0]->out;
            channel->out[0] = &channel->slots[1]->out;
            channel->out[1] = &channel->chip->zeromod;
            channel->out[2] = &channel->chip->zeromod;
            channel->out[3] = &channel->chip->zeromod;
            break;
        case 0x01:
            channel->slots[0]->mod = &channel->slots[0]->fbmod;
            channel->slots[1]->mod = &channel->chip->zeromod;
            channel->out[0] = &channel->slots[0]->out;
            channel->out[1] = &channel->slots[1]->out;
            channel->out[2] = &channel->chip->zeromod;
            channel->out[3] = &channel->chip->zeromod;
            break;
        }
    }
}
 
static void OPL3_ChannelWriteC0(opl3_channel *channel, uint8_t data)
{
    channel->fb = (data & 0x0e) >> 1;
    channel->con = data & 0x01;
    channel->alg = channel->con;
    if (channel->chip->newm)
    {
        if (channel->chtype == ch_4op)
        {
            channel->pair->alg = 0x04 | (channel->con << 1) | (channel->pair->con);
            channel->alg = 0x08;
            OPL3_ChannelSetupAlg(channel->pair);
        }
        else if (channel->chtype == ch_4op2)
        {
            channel->alg = 0x04 | (channel->pair->con << 1) | (channel->con);
            channel->pair->alg = 0x08;
            OPL3_ChannelSetupAlg(channel);
        }
        else
        {
            OPL3_ChannelSetupAlg(channel);
        }
    }
    else
    {
        OPL3_ChannelSetupAlg(channel);
    }
    if (channel->chip->newm)
    {
        channel->cha = ((data >> 4) & 0x01) ? ~0 : 0;
        channel->chb = ((data >> 5) & 0x01) ? ~0 : 0;
    }
    else
    {
        channel->cha = channel->chb = (uint16_t)~0;
    }
}
 
static void OPL3_ChannelKeyOn(opl3_channel *channel)
{
    if (channel->chip->newm)
    {
        if (channel->chtype == ch_4op)
        {
            OPL3_EnvelopeKeyOn(channel->slots[0], egk_norm);
            OPL3_EnvelopeKeyOn(channel->slots[1], egk_norm);
            OPL3_EnvelopeKeyOn(channel->pair->slots[0], egk_norm);
            OPL3_EnvelopeKeyOn(channel->pair->slots[1], egk_norm);
        }
        else if (channel->chtype == ch_2op || channel->chtype == ch_drum)
        {
            OPL3_EnvelopeKeyOn(channel->slots[0], egk_norm);
            OPL3_EnvelopeKeyOn(channel->slots[1], egk_norm);
        }
    }
    else
    {
        OPL3_EnvelopeKeyOn(channel->slots[0], egk_norm);
        OPL3_EnvelopeKeyOn(channel->slots[1], egk_norm);
    }
}
 
static void OPL3_ChannelKeyOff(opl3_channel *channel)
{
    if (channel->chip->newm)
    {
        if (channel->chtype == ch_4op)
        {
            OPL3_EnvelopeKeyOff(channel->slots[0], egk_norm);
            OPL3_EnvelopeKeyOff(channel->slots[1], egk_norm);
            OPL3_EnvelopeKeyOff(channel->pair->slots[0], egk_norm);
            OPL3_EnvelopeKeyOff(channel->pair->slots[1], egk_norm);
        }
        else if (channel->chtype == ch_2op || channel->chtype == ch_drum)
        {
            OPL3_EnvelopeKeyOff(channel->slots[0], egk_norm);
            OPL3_EnvelopeKeyOff(channel->slots[1], egk_norm);
        }
    }
    else
    {
        OPL3_EnvelopeKeyOff(channel->slots[0], egk_norm);
        OPL3_EnvelopeKeyOff(channel->slots[1], egk_norm);
    }
}
 
static void OPL3_ChannelSet4Op(opl3_chip *chip, uint8_t data)
{
    uint8_t bit;
    uint8_t chnum;
    for (bit = 0; bit < 6; bit++)
    {
        chnum = bit;
        if (bit >= 3)
        {
            chnum += 9 - 3;
        }
        if ((data >> bit) & 0x01)
        {
            chip->channel[chnum].chtype = ch_4op;
            chip->channel[chnum + 3].chtype = ch_4op2;
        }
        else
        {
            chip->channel[chnum].chtype = ch_2op;
            chip->channel[chnum + 3].chtype = ch_2op;
        }
    }
}
 
static int16_t OPL3_ClipSample(int32_t sample)
{
    if (sample > 32767)
    {
        sample = 32767;
    }
    else if (sample < -32768)
    {
        sample = -32768;
    }
    return (int16_t)sample;
}
 
void OPL3_Generate(opl3_chip *chip, int16_t *buf)
{
    uint8_t ii;
    uint8_t jj;
    int16_t accm;
    uint8_t shift = 0;
 
    buf[1] = OPL3_ClipSample(chip->mixbuff[1]);
 
    for (ii = 0; ii < 15; ii++)
    {
        OPL3_SlotCalcFB(&chip->slot[ii]);
        OPL3_EnvelopeCalc(&chip->slot[ii]);
        OPL3_PhaseGenerate(&chip->slot[ii]);
        OPL3_SlotGenerate(&chip->slot[ii]);
    }
 
    chip->mixbuff[0] = 0;
    for (ii = 0; ii < 18; ii++)
    {
        accm = 0;
        for (jj = 0; jj < 4; jj++)
        {
            accm += *chip->channel[ii].out[jj];
        }
        chip->mixbuff[0] += (int16_t)(accm & chip->channel[ii].cha);
    }
 
    for (ii = 15; ii < 18; ii++)
    {
        OPL3_SlotCalcFB(&chip->slot[ii]);
        OPL3_EnvelopeCalc(&chip->slot[ii]);
        OPL3_PhaseGenerate(&chip->slot[ii]);
        OPL3_SlotGenerate(&chip->slot[ii]);
    }
 
    buf[0] = OPL3_ClipSample(chip->mixbuff[0]);
 
    for (ii = 18; ii < 33; ii++)
    {
        OPL3_SlotCalcFB(&chip->slot[ii]);
        OPL3_EnvelopeCalc(&chip->slot[ii]);
        OPL3_PhaseGenerate(&chip->slot[ii]);
        OPL3_SlotGenerate(&chip->slot[ii]);
    }
 
    chip->mixbuff[1] = 0;
    for (ii = 0; ii < 18; ii++)
    {
        accm = 0;
        for (jj = 0; jj < 4; jj++)
        {
            accm += *chip->channel[ii].out[jj];
        }
        chip->mixbuff[1] += (int16_t)(accm & chip->channel[ii].chb);
    }
 
    for (ii = 33; ii < 36; ii++)
    {
        OPL3_SlotCalcFB(&chip->slot[ii]);
        OPL3_EnvelopeCalc(&chip->slot[ii]);
        OPL3_PhaseGenerate(&chip->slot[ii]);
        OPL3_SlotGenerate(&chip->slot[ii]);
    }
 
    if ((chip->timer & 0x3f) == 0x3f)
    {
        chip->tremolopos = (chip->tremolopos + 1) % 210;
    }
    if (chip->tremolopos < 105)
    {
        chip->tremolo = chip->tremolopos >> chip->tremoloshift;
    }
    else
    {
        chip->tremolo = (210 - chip->tremolopos) >> chip->tremoloshift;
    }
 
    if ((chip->timer & 0x3ff) == 0x3ff)
    {
        chip->vibpos = (chip->vibpos + 1) & 7;
    }
 
    chip->timer++;
 
    chip->eg_add = 0;
    if (chip->eg_timer)
    {
        while (shift < 36 && ((chip->eg_timer >> shift) & 1) == 0)
        {
            shift++;
        }
        if (shift > 12)
        {
            chip->eg_add = 0;
        }
        else
        {
            chip->eg_add = shift + 1;
        }
    }
 
    if (chip->eg_timerrem || chip->eg_state)
    {
        if (chip->eg_timer == 0xfffffffff)
        {
            chip->eg_timer = 0;
            chip->eg_timerrem = 1;
        }
        else
        {
            chip->eg_timer++;
            chip->eg_timerrem = 0;
        }
    }
 
    chip->eg_state ^= 1;
 
    while (chip->writebuf[chip->writebuf_cur].time <= chip->writebuf_samplecnt)
    {
        if (!(chip->writebuf[chip->writebuf_cur].reg & 0x200))
        {
            break;
        }
        chip->writebuf[chip->writebuf_cur].reg &= 0x1ff;
        OPL3_WriteReg(chip, chip->writebuf[chip->writebuf_cur].reg,
                      chip->writebuf[chip->writebuf_cur].data);
        chip->writebuf_cur = (chip->writebuf_cur + 1) % OPL_WRITEBUF_SIZE;
    }
    chip->writebuf_samplecnt++;
}
 
void OPL3_GenerateResampled(opl3_chip *chip, int16_t *buf1, int16_t *buf2)
{
    while (chip->samplecnt >= chip->rateratio)
    {
        chip->oldsamples[0] = chip->samples[0];
        chip->oldsamples[1] = chip->samples[1];
        OPL3_Generate(chip, chip->samples);
        chip->samplecnt -= chip->rateratio;
    }
    buf1[0] = (int16_t)((chip->oldsamples[0] * (chip->rateratio - chip->samplecnt)
                     + chip->samples[0] * chip->samplecnt) / chip->rateratio);
    buf2[0] = (int16_t)((chip->oldsamples[1] * (chip->rateratio - chip->samplecnt)
                     + chip->samples[1] * chip->samplecnt) / chip->rateratio);
    chip->samplecnt += 1 << RSM_FRAC;
}
 
void OPL3_Reset(opl3_chip *chip, uint32_t samplerate)
{
    uint8_t slotnum;
    uint8_t channum;
 
    memset(chip, 0, sizeof(opl3_chip));
    for (slotnum = 0; slotnum < 36; slotnum++)
    {
        chip->slot[slotnum].chip = chip;
        chip->slot[slotnum].mod = &chip->zeromod;
        chip->slot[slotnum].eg_rout = 0x1ff;
        chip->slot[slotnum].eg_out = 0x1ff;
        chip->slot[slotnum].eg_gen = envelope_gen_num_release;
        chip->slot[slotnum].trem = (uint8_t*)&chip->zeromod;
        chip->slot[slotnum].slot_num = slotnum;
    }
    for (channum = 0; channum < 18; channum++)
    {
        chip->channel[channum].slots[0] = &chip->slot[ch_slot[channum]];
        chip->channel[channum].slots[1] = &chip->slot[ch_slot[channum] + 3];
        chip->slot[ch_slot[channum]].channel = &chip->channel[channum];
        chip->slot[ch_slot[channum] + 3].channel = &chip->channel[channum];
        if ((channum % 9) < 3)
        {
            chip->channel[channum].pair = &chip->channel[channum + 3];
        }
        else if ((channum % 9) < 6)
        {
            chip->channel[channum].pair = &chip->channel[channum - 3];
        }
        chip->channel[channum].chip = chip;
        chip->channel[channum].out[0] = &chip->zeromod;
        chip->channel[channum].out[1] = &chip->zeromod;
        chip->channel[channum].out[2] = &chip->zeromod;
        chip->channel[channum].out[3] = &chip->zeromod;
        chip->channel[channum].chtype = ch_2op;
        chip->channel[channum].cha = 0xffff;
        chip->channel[channum].chb = 0xffff;
        chip->channel[channum].ch_num = channum;
        OPL3_ChannelSetupAlg(&chip->channel[channum]);
    }
    chip->noise = 1;
    chip->rateratio = (samplerate << RSM_FRAC) / 49716;
    chip->tremoloshift = 4;
    chip->vibshift = 1;
}
 
void OPL3_WriteReg(opl3_chip *chip, uint16_t reg, uint8_t v)
{
    uint8_t high = (reg >> 8) & 0x01;
    uint8_t regm = reg & 0xff;
    switch (regm & 0xf0)
    {
    case 0x00:
        if (high)
        {
            switch (regm & 0x0f)
            {
            case 0x04:
                OPL3_ChannelSet4Op(chip, v);
                break;
            case 0x05:
                chip->newm = v & 0x01;
                break;
            }
        }
        else
        {
            switch (regm & 0x0f)
            {
            case 0x08:
                chip->nts = (v >> 6) & 0x01;
                break;
            }
        }
        break;
    case 0x20:
    case 0x30:
        if (ad_slot[regm & 0x1f] >= 0)
        {
            OPL3_SlotWrite20(&chip->slot[18 * high + ad_slot[regm & 0x1f]], v);
        }
        break;
    case 0x40:
    case 0x50:
        if (ad_slot[regm & 0x1f] >= 0)
        {
            OPL3_SlotWrite40(&chip->slot[18 * high + ad_slot[regm & 0x1f]], v);
        }
        break;
    case 0x60:
    case 0x70:
        if (ad_slot[regm & 0x1f] >= 0)
        {
            OPL3_SlotWrite60(&chip->slot[18 * high + ad_slot[regm & 0x1f]], v);
        }
        break;
    case 0x80:
    case 0x90:
        if (ad_slot[regm & 0x1f] >= 0)
        {
            OPL3_SlotWrite80(&chip->slot[18 * high + ad_slot[regm & 0x1f]], v);
        }
        break;
    case 0xe0:
    case 0xf0:
        if (ad_slot[regm & 0x1f] >= 0)
        {
            OPL3_SlotWriteE0(&chip->slot[18 * high + ad_slot[regm & 0x1f]], v);
        }
        break;
    case 0xa0:
        if ((regm & 0x0f) < 9)
        {
            OPL3_ChannelWriteA0(&chip->channel[9 * high + (regm & 0x0f)], v);
        }
        break;
    case 0xb0:
        if (regm == 0xbd && !high)
        {
            chip->tremoloshift = (((v >> 7) ^ 1) << 1) + 2;
            chip->vibshift = ((v >> 6) & 0x01) ^ 1;
            OPL3_ChannelUpdateRhythm(chip, v);
        }
        else if ((regm & 0x0f) < 9)
        {
            OPL3_ChannelWriteB0(&chip->channel[9 * high + (regm & 0x0f)], v);
            if (v & 0x20)
            {
                OPL3_ChannelKeyOn(&chip->channel[9 * high + (regm & 0x0f)]);
            }
            else
            {
                OPL3_ChannelKeyOff(&chip->channel[9 * high + (regm & 0x0f)]);
            }
        }
        break;
    case 0xc0:
        if ((regm & 0x0f) < 9)
        {
            OPL3_ChannelWriteC0(&chip->channel[9 * high + (regm & 0x0f)], v);
        }
        break;
    }
}
 
void OPL3_WriteRegBuffered(opl3_chip *chip, uint16_t reg, uint8_t v)
{
    uint64_t time1, time2;
 
    if (chip->writebuf[chip->writebuf_last].reg & 0x200)
    {
        OPL3_WriteReg(chip, chip->writebuf[chip->writebuf_last].reg & 0x1ff,
                      chip->writebuf[chip->writebuf_last].data);
 
        chip->writebuf_cur = (chip->writebuf_last + 1) % OPL_WRITEBUF_SIZE;
        chip->writebuf_samplecnt = chip->writebuf[chip->writebuf_last].time;
    }
 
    chip->writebuf[chip->writebuf_last].reg = reg | 0x200;
    chip->writebuf[chip->writebuf_last].data = v;
    time1 = chip->writebuf_lasttime + OPL_WRITEBUF_DELAY;
    time2 = chip->writebuf_samplecnt;
 
    if (time1 < time2)
    {
        time1 = time2;
    }
 
    chip->writebuf[chip->writebuf_last].time = time1;
    chip->writebuf_lasttime = time1;
    chip->writebuf_last = (chip->writebuf_last + 1) % OPL_WRITEBUF_SIZE;
}
 
void OPL3_GenerateStream(opl3_chip *chip, int16_t *sndptr1, int16_t *sndptr2, uint32_t numsamples, const uint32_t increment1, const uint32_t increment2 )
{
    /* Comment from LGB:
       Originally Nuked-OPL3 generated interleaved stereo stream (see the "original code was" part above).
       I modified this to have two buffer pointers passed, and also too increment values.
       This way, the interleaved scheme can be still 'simulated' but also, separate buffers can be used,
       what is my intent for Xemu.
    */
    while (numsamples--) {
        OPL3_GenerateResampled(chip, sndptr1, sndptr2);
        sndptr1 += increment1;
        sndptr2 += increment2;
    }
    /* // Original code was:
    uint32_t i;
 
    for(i = 0; i < numsamples; i++)
    {
        OPL3_GenerateResampled(chip, sndptr);
        sndptr += 2;
    }
    */
}