view snes_spc/SPC_Filter.cpp @ 2:c3248c71ae74

begin convert program
author Robert McIntyre <rlm@mit.edu>
date Fri, 21 Oct 2011 06:21:33 -0700
parents e38dacceb958
children
line wrap: on
line source
1 // snes_spc 0.9.0. http://www.slack.net/~ant/
3 #include "SPC_Filter.h"
5 #include <string.h>
7 /* Copyright (C) 2007 Shay Green. This module is free software; you
8 can redistribute it and/or modify it under the terms of the GNU Lesser
9 General Public License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version. This
11 module is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
13 FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
14 details. You should have received a copy of the GNU Lesser General Public
15 License along with this module; if not, write to the Free Software Foundation,
16 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
18 #include "blargg_source.h"
20 void SPC_Filter::clear() { memset( ch, 0, sizeof ch ); }
22 SPC_Filter::SPC_Filter()
23 {
24 gain = gain_unit;
25 bass = bass_norm;
26 clear();
27 }
29 void SPC_Filter::run( short* io, int count )
30 {
31 require( (count & 1) == 0 ); // must be even
33 int const gain = this->gain;
34 int const bass = this->bass;
35 chan_t* c = &ch [2];
36 do
37 {
38 // cache in registers
39 int sum = (--c)->sum;
40 int pp1 = c->pp1;
41 int p1 = c->p1;
43 for ( int i = 0; i < count; i += 2 )
44 {
45 // Low-pass filter (two point FIR with coeffs 0.25, 0.75)
46 int f = io [i] + p1;
47 p1 = io [i] * 3;
49 // High-pass filter ("leaky integrator")
50 int delta = f - pp1;
51 pp1 = f;
52 int s = sum >> (gain_bits + 2);
53 sum += (delta * gain) - (sum >> bass);
55 // Clamp to 16 bits
56 if ( (short) s != s )
57 s = (s >> 31) ^ 0x7FFF;
59 io [i] = (short) s;
60 }
62 c->p1 = p1;
63 c->pp1 = pp1;
64 c->sum = sum;
65 ++io;
66 }
67 while ( c != ch );
68 }