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1 // snes_spc 0.9.0. http://www.slack.net/~ant/
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2
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3 #include "SPC_Filter.h"
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4
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5 #include <string.h>
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6
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7 /* Copyright (C) 2007 Shay Green. This module is free software; you
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8 can redistribute it and/or modify it under the terms of the GNU Lesser
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9 General Public License as published by the Free Software Foundation; either
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10 version 2.1 of the License, or (at your option) any later version. This
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11 module is distributed in the hope that it will be useful, but WITHOUT ANY
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12 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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13 FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
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14 details. You should have received a copy of the GNU Lesser General Public
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15 License along with this module; if not, write to the Free Software Foundation,
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16 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
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17
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18 #include "blargg_source.h"
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19
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20 void SPC_Filter::clear() { memset( ch, 0, sizeof ch ); }
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21
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22 SPC_Filter::SPC_Filter()
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23 {
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24 gain = gain_unit;
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25 bass = bass_norm;
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26 clear();
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27 }
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28
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29 void SPC_Filter::run( short* io, int count )
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30 {
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31 require( (count & 1) == 0 ); // must be even
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32
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33 int const gain = this->gain;
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34 int const bass = this->bass;
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35 chan_t* c = &ch [2];
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36 do
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37 {
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38 // cache in registers
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39 int sum = (--c)->sum;
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40 int pp1 = c->pp1;
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41 int p1 = c->p1;
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42
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43 for ( int i = 0; i < count; i += 2 )
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44 {
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45 // Low-pass filter (two point FIR with coeffs 0.25, 0.75)
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46 int f = io [i] + p1;
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47 p1 = io [i] * 3;
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48
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49 // High-pass filter ("leaky integrator")
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50 int delta = f - pp1;
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51 pp1 = f;
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52 int s = sum >> (gain_bits + 2);
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53 sum += (delta * gain) - (sum >> bass);
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54
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55 // Clamp to 16 bits
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56 if ( (short) s != s )
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57 s = (s >> 31) ^ 0x7FFF;
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58
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59 io [i] = (short) s;
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60 }
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61
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62 c->p1 = p1;
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63 c->pp1 = pp1;
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64 c->sum = sum;
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65 ++io;
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66 }
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67 while ( c != ch );
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68 }
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