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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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