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718112a8fe
Currently none of these is being used, but eventually they will, once more code gets ported over. So it's better to have them right away and avoid editing the project file too much, only to revert that later.
97 lines
2.8 KiB
C++
97 lines
2.8 KiB
C++
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
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#include "Kss_Scc_Apu.h"
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/* Copyright (C) 2006 Shay Green. This module is free software; you
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can redistribute it and/or modify it under the terms of the GNU Lesser
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General Public License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version. This
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module is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
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details. You should have received a copy of the GNU Lesser General Public
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License along with this module; if not, write to the Free Software Foundation,
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Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
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#include "blargg_source.h"
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// Tones above this frequency are treated as disabled tone at half volume.
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// Power of two is more efficient (avoids division).
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unsigned const inaudible_freq = 16384;
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int const wave_size = 0x20;
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void Scc_Apu::run_until( blip_time_t end_time )
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{
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for ( int index = 0; index < osc_count; index++ )
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{
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osc_t& osc = oscs [index];
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Blip_Buffer* const output = osc.output;
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if ( !output )
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continue;
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output->set_modified();
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blip_time_t period = (regs [0x80 + index * 2 + 1] & 0x0F) * 0x100 +
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regs [0x80 + index * 2] + 1;
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int volume = 0;
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if ( regs [0x8F] & (1 << index) )
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{
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blip_time_t inaudible_period = (blargg_ulong) (output->clock_rate() +
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inaudible_freq * 32) / (inaudible_freq * 16);
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if ( period > inaudible_period )
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volume = (regs [0x8A + index] & 0x0F) * (amp_range / 256 / 15);
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}
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int8_t const* wave = (int8_t*) regs + index * wave_size;
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if ( index == osc_count - 1 )
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wave -= wave_size; // last two oscs share wave
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{
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int amp = wave [osc.phase] * volume;
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int delta = amp - osc.last_amp;
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if ( delta )
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{
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osc.last_amp = amp;
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synth.offset( last_time, delta, output );
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}
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}
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blip_time_t time = last_time + osc.delay;
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if ( time < end_time )
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{
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if ( !volume )
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{
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// maintain phase
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blargg_long count = (end_time - time + period - 1) / period;
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osc.phase = (osc.phase + count) & (wave_size - 1);
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time += count * period;
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}
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else
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{
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int phase = osc.phase;
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int last_wave = wave [phase];
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phase = (phase + 1) & (wave_size - 1); // pre-advance for optimal inner loop
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do
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{
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int amp = wave [phase];
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phase = (phase + 1) & (wave_size - 1);
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int delta = amp - last_wave;
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if ( delta )
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{
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last_wave = amp;
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synth.offset( time, delta * volume, output );
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}
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time += period;
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}
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while ( time < end_time );
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osc.phase = phase = (phase - 1) & (wave_size - 1); // undo pre-advance
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osc.last_amp = wave [phase] * volume;
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}
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}
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osc.delay = time - end_time;
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}
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last_time = end_time;
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}
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