rlm@0: // snes_spc 0.9.0. http://www.slack.net/~ant/
rlm@0: 
rlm@0: #include "SPC_Filter.h"
rlm@0: 
rlm@0: #include <string.h>
rlm@0: 
rlm@0: /* Copyright (C) 2007 Shay Green. This module is free software; you
rlm@0: can redistribute it and/or modify it under the terms of the GNU Lesser
rlm@0: General Public License as published by the Free Software Foundation; either
rlm@0: version 2.1 of the License, or (at your option) any later version. This
rlm@0: module is distributed in the hope that it will be useful, but WITHOUT ANY
rlm@0: WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
rlm@0: FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
rlm@0: details. You should have received a copy of the GNU Lesser General Public
rlm@0: License along with this module; if not, write to the Free Software Foundation,
rlm@0: Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
rlm@0: 
rlm@0: #include "blargg_source.h"
rlm@0: 
rlm@0: void SPC_Filter::clear() { memset( ch, 0, sizeof ch ); }
rlm@0: 
rlm@0: SPC_Filter::SPC_Filter()
rlm@0: {
rlm@0: 	gain = gain_unit;
rlm@0: 	bass = bass_norm;
rlm@0: 	clear();
rlm@0: }
rlm@0: 
rlm@0: void SPC_Filter::run( short* io, int count )
rlm@0: {
rlm@0: 	require( (count & 1) == 0 ); // must be even
rlm@0: 	
rlm@0: 	int const gain = this->gain;
rlm@0: 	int const bass = this->bass;
rlm@0: 	chan_t* c = &ch [2];
rlm@0: 	do
rlm@0: 	{
rlm@0: 		// cache in registers
rlm@0: 		int sum = (--c)->sum;
rlm@0: 		int pp1 = c->pp1;
rlm@0: 		int p1  = c->p1;
rlm@0: 		
rlm@0: 		for ( int i = 0; i < count; i += 2 )
rlm@0: 		{
rlm@0: 			// Low-pass filter (two point FIR with coeffs 0.25, 0.75)
rlm@0: 			int f = io [i] + p1;
rlm@0: 			p1 = io [i] * 3;
rlm@0: 			
rlm@0: 			// High-pass filter ("leaky integrator")
rlm@0: 			int delta = f - pp1;
rlm@0: 			pp1 = f;
rlm@0: 			int s = sum >> (gain_bits + 2);
rlm@0: 			sum += (delta * gain) - (sum >> bass);
rlm@0: 			
rlm@0: 			// Clamp to 16 bits
rlm@0: 			if ( (short) s != s )
rlm@0: 				s = (s >> 31) ^ 0x7FFF;
rlm@0: 			
rlm@0: 			io [i] = (short) s;
rlm@0: 		}
rlm@0: 		
rlm@0: 		c->p1  = p1;
rlm@0: 		c->pp1 = pp1;
rlm@0: 		c->sum = sum;
rlm@0: 		++io;
rlm@0: 	}
rlm@0: 	while ( c != ch );
rlm@0: }