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Spc_Filter.cpp
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Spc_Filter.cpp
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// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
#include "Spc_Filter.h"
#include <string.h>
/* Copyright (C) 2007 Shay Green. This module 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
module 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 module; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
#include "blargg_source.h"
void SPC_Filter::clear() { memset( ch, 0, sizeof ch ); }
SPC_Filter::SPC_Filter()
{
enabled = true;
gain = gain_unit;
bass = bass_norm;
clear();
}
void SPC_Filter::run( short* io, int count )
{
require( (count & 1) == 0 ); // must be even
int const gain = this->gain;
if ( enabled )
{
int const bass = this->bass;
chan_t* c = &ch [2];
do
{
// cache in registers
int sum = (--c)->sum;
int pp1 = c->pp1;
int p1 = c->p1;
for ( int i = 0; i < count; i += 2 )
{
// Low-pass filter (two point FIR with coeffs 0.25, 0.75)
int f = io [i] + p1;
p1 = io [i] * 3;
// High-pass filter ("leaky integrator")
int delta = f - pp1;
pp1 = f;
int s = sum >> (gain_bits + 2);
sum += (delta * gain) - (sum >> bass);
// Clamp to 16 bits
if ( (short) s != s )
s = (s >> 31) ^ 0x7FFF;
io [i] = (short) s;
}
c->p1 = p1;
c->pp1 = pp1;
c->sum = sum;
++io;
}
while ( c != ch );
}
else if ( gain != gain_unit )
{
short* const end = io + count;
while ( io < end )
{
int s = (*io * gain) >> gain_bits;
if ( (short) s != s )
s = (s >> 31) ^ 0x7FFF;
*io++ = (short) s;
}
}
}

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Spc_Filter.cpp (2 KB)

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