src/mt32/Tables.cpp

/* Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009 Dean Beeler, Jerome Fisher
 * Copyright (C) 2011, 2012, 2013 Dean Beeler, Jerome Fisher, Sergey V. Mikayev
 *
 *  This program 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.
 *
 *  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 Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <cmath>
#include <cstdlib>
#include <cstring>

#include "mt32emu.h"
#include "mmath.h"

namespace MT32Emu {

const Tables &Tables::getInstance() {
        static const Tables instance;
        return instance;
}

Tables::Tables() {
        int lf;
        for (lf = 0; lf <= 100; lf++) {
                // CONFIRMED:KG: This matches a ROM table found by Mok
                float fVal = (2.0f - LOG10F((float)lf + 1.0f)) * 128.0f;
                int val = (int)(fVal + 1.0);
                if (val > 255) {
                        val = 255;
                }
                levelToAmpSubtraction[lf] = (Bit8u)val;
        }

        envLogarithmicTime[0] = 64;
        for (lf = 1; lf <= 255; lf++) {
                // CONFIRMED:KG: This matches a ROM table found by Mok
                envLogarithmicTime[lf] = (Bit8u)ceil(64.0f + LOG2F((float)lf) * 8.0f);
        }

#ifdef EMULATE_LAPC_I // Dummy #ifdef - we'll have runtime emulation mode selection in future.
        // CONFIRMED: Based on a table found by Mok in the LAPC-I control ROM
        // Note that this matches the MT-32 table, but with the values clamped to a maximum of 8.
        memset(masterVolToAmpSubtraction, 8, 71);
        memset(masterVolToAmpSubtraction + 71, 7, 3);
        memset(masterVolToAmpSubtraction + 74, 6, 4);
        memset(masterVolToAmpSubtraction + 78, 5, 3);
        memset(masterVolToAmpSubtraction + 81, 4, 4);
        memset(masterVolToAmpSubtraction + 85, 3, 3);
        memset(masterVolToAmpSubtraction + 88, 2, 4);
        memset(masterVolToAmpSubtraction + 92, 1, 4);
        memset(masterVolToAmpSubtraction + 96, 0, 5);
#else
        // CONFIRMED: Based on a table found by Mok in the MT-32 control ROM
        masterVolToAmpSubtraction[0] = 255;
        for (int masterVol = 1; masterVol <= 100; masterVol++) {
        masterVolToAmpSubtraction[masterVol] = (Bit8u)(106.31 - 16.0 * LOG2F((float)masterVol));
        }
#endif

        for (int i = 0; i <= 100; i++) {
                pulseWidth100To255[i] = (Bit8u)(i * 255 / 100.0f + 0.5f);
                //synth->printDebug("%d: %d", i, pulseWidth100To255[i]);
        }

        // The LA32 chip contains an exponent table inside. The table contains 12-bit integer values.
        // The actual table size is 512 rows. The 9 higher bits of the fractional part of the argument are used as a lookup address.
        // To improve the precision of computations, the lower bits are supposed to be used for interpolation as the LA32 chip also
        // contains another 512-row table with inverted differences between the main table values.
        for (int i = 0; i < 512; i++) {
                exp9[i] = Bit16u(8191.5f - EXP2F(13.0f + ~i / 512.0f));
        }

        // There is a logarithmic sine table inside the LA32 chip. The table contains 13-bit integer values.
        for (int i = 1; i < 512; i++) {
                logsin9[i] = Bit16u(0.5f - LOG2F(sin((i + 0.5f) / 1024.0f * FLOAT_PI)) * 1024.0f);
        }

        // The very first value is clamped to the maximum possible 13-bit integer
        logsin9[0] = 8191;

        // found from sample analysis
        static const Bit8u resAmpDecayFactorTable[] = {31, 16, 12, 8, 5, 3, 2, 1};
        resAmpDecayFactor = resAmpDecayFactorTable;
}

}