Mercurial > spc_convert

     1 // snes_spc 0.9.0. http://www.slack.net/~ant/

     2 

     3 #include "SPC_Filter.h"

     4 

     5 #include <string.h>

     6 

     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 */

    17 

    18 #include "blargg_source.h"

    19 

    20 void SPC_Filter::clear() { memset( ch, 0, sizeof ch ); }

    21 

    22 SPC_Filter::SPC_Filter()

    23 {

    24 	gain = gain_unit;

    25 	bass = bass_norm;

    26 	clear();

    27 }

    28 

    29 void SPC_Filter::run( short* io, int count )

    30 {

    31 	require( (count & 1) == 0 ); // must be even

    32 	

    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;

    42 		

    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;

    48 			

    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);

    54 			

    55 			// Clamp to 16 bits

    56 			if ( (short) s != s )

    57 				s = (s >> 31) ^ 0x7FFF;

    58 			

    59 			io [i] = (short) s;

    60 		}

    61 		

    62 		c->p1  = p1;

    63 		c->pp1 = pp1;

    64 		c->sum = sum;

    65 		++io;

    66 	}

    67 	while ( c != ch );

    68 }
author	Robert McIntyre <rlm@mit.edu>
date	Fri, 21 Oct 2011 05:53:11 -0700
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