84 lines
2.0 KiB
C++
84 lines
2.0 KiB
C++
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
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#include "Spc_Filter.h"
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#include <string.h>
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/* Copyright (C) 2007 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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void SPC_Filter::clear() { memset( ch, 0, sizeof ch ); }
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SPC_Filter::SPC_Filter()
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{
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enabled = true;
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gain = gain_unit;
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bass = bass_norm;
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clear();
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}
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void SPC_Filter::run( short* io, int count )
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{
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require( (count & 1) == 0 ); // must be even
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int const gain = this->gain;
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if ( enabled )
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{
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int const bass = this->bass;
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chan_t* c = &ch [2];
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do
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{
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// cache in registers
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int sum = (--c)->sum;
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int pp1 = c->pp1;
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int p1 = c->p1;
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for ( int i = 0; i < count; i += 2 )
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{
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// Low-pass filter (two point FIR with coeffs 0.25, 0.75)
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int f = io [i] + p1;
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p1 = io [i] * 3;
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// High-pass filter ("leaky integrator")
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int delta = f - pp1;
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pp1 = f;
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int s = sum >> (gain_bits + 2);
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sum += (delta * gain) - (sum >> bass);
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// Clamp to 16 bits
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if ( (short) s != s )
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s = (s >> 31) ^ 0x7FFF;
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io [i] = (short) s;
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}
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c->p1 = p1;
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c->pp1 = pp1;
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c->sum = sum;
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++io;
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}
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while ( c != ch );
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}
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else if ( gain != gain_unit )
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{
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short* const end = io + count;
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while ( io < end )
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{
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int s = (*io * gain) >> gain_bits;
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if ( (short) s != s )
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s = (s >> 31) ^ 0x7FFF;
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*io++ = (short) s;
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}
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}
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}
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