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/*
* This program is free software; you can redistribute it and modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the license or (at your
* option) any later version.
*
* Authors: Markus Fick <webmaster@mark-f.de> fir-resampler, technical information
* Chris Moeller <chris@kode54.net> Table/struct file generator
*
*/
#include <math.h>
#include <stdio.h>
/*
------------------------------------------------------------------------------------------------
fir interpolation doc,
(derived from "an engineer's guide to fir digital filters", n.j. loy)
calculate coefficients for ideal lowpass filter (with cutoff = fc in 0..1 (mapped to 0..nyquist))
c[-N..N] = (i==0) ? fc : sin(fc*pi*i)/(pi*i)
then apply selected window to coefficients
c[-N..N] *= w(0..N)
with n in 2*N and w(n) being a window function (see loy)
then calculate gain and scale filter coefs to have unity gain.
------------------------------------------------------------------------------------------------
*/
// quantizer scale of window coefs
#define WFIR_QUANTBITS 14
#define WFIR_QUANTSCALE (1L<<WFIR_QUANTBITS)
#define WFIR_8SHIFT (WFIR_QUANTBITS-8)
#define WFIR_16BITSHIFT (WFIR_QUANTBITS)
// log2(number)-1 of precalculated taps range is [4..12]
#define WFIR_FRACBITS 10
#define WFIR_LUTLEN ((1L<<(WFIR_FRACBITS+1))+1)
// number of samples in window
#define WFIR_LOG2WIDTH 3
#define WFIR_WIDTH (1L<<WFIR_LOG2WIDTH)
#define WFIR_SMPSPERWING ((WFIR_WIDTH-1)>>1)
// cutoff (1.0 == pi/2)
#define WFIR_CUTOFF 0.90f
#define WFIR_CUTOFFBITS 9
#define WFIR_CUTOFFLEN ((1L<<(WFIR_CUTOFFBITS))+1)
// wfir type
#define WFIR_HANN 0
#define WFIR_HAMMING 1
#define WFIR_BLACKMANEXACT 2
#define WFIR_BLACKMAN3T61 3
#define WFIR_BLACKMAN3T67 4
#define WFIR_BLACKMAN4T92 5
#define WFIR_BLACKMAN4T74 6
#define WFIR_KAISER4T 7
#define WFIR_TYPE WFIR_BLACKMANEXACT
// wfir help
#ifndef M_zPI
#define M_zPI 3.1415926535897932384626433832795
#endif
#define M_zEPS 1e-8
#define M_zBESSELEPS 1e-21
class CzWINDOWEDFIR
{ public:
CzWINDOWEDFIR( );
~CzWINDOWEDFIR( );
float coef( int _PCnr, float _POfs, float _PCut, int _PWidth, int _PType ) //float _PPos, float _PFc, int _PLen )
{ double _LWidthM1 = _PWidth-1;
double _LWidthM1Half = 0.5*_LWidthM1;
double _LPosU = ((double)_PCnr - _POfs);
double _LPos = _LPosU-_LWidthM1Half;
double _LPIdl = 2.0*M_zPI/_LWidthM1;
double _LWc,_LSi;
if( fabs(_LPos)<M_zEPS )
{ _LWc = 1.0;
_LSi = _PCut;
}
else
{ switch( _PType )
{ case WFIR_HANN:
_LWc = 0.50 - 0.50 * cos(_LPIdl*_LPosU);
break;
case WFIR_HAMMING:
_LWc = 0.54 - 0.46 * cos(_LPIdl*_LPosU);
break;
case WFIR_BLACKMANEXACT:
_LWc = 0.42 - 0.50 * cos(_LPIdl*_LPosU) + 0.08 * cos(2.0*_LPIdl*_LPosU);
break;
case WFIR_BLACKMAN3T61:
_LWc = 0.44959 - 0.49364 * cos(_LPIdl*_LPosU) + 0.05677 * cos(2.0*_LPIdl*_LPosU);
break;
case WFIR_BLACKMAN3T67:
_LWc = 0.42323 - 0.49755 * cos(_LPIdl*_LPosU) + 0.07922 * cos(2.0*_LPIdl*_LPosU);
break;
case WFIR_BLACKMAN4T92:
_LWc = 0.35875 - 0.48829 * cos(_LPIdl*_LPosU) + 0.14128 * cos(2.0*_LPIdl*_LPosU) - 0.01168 * cos(3.0*_LPIdl*_LPosU);
break;
case WFIR_BLACKMAN4T74:
_LWc = 0.40217 - 0.49703 * cos(_LPIdl*_LPosU) + 0.09392 * cos(2.0*_LPIdl*_LPosU) - 0.00183 * cos(3.0*_LPIdl*_LPosU);
break;
case WFIR_KAISER4T:
_LWc = 0.40243 - 0.49804 * cos(_LPIdl*_LPosU) + 0.09831 * cos(2.0*_LPIdl*_LPosU) - 0.00122 * cos(3.0*_LPIdl*_LPosU);
break;
default:
_LWc = 1.0;
break;
}
_LPos *= M_zPI;
_LSi = sin(_PCut*_LPos)/_LPos;
}
return (float)(_LWc*_LSi);
}
static signed short lut[WFIR_LUTLEN*WFIR_WIDTH];
};
signed short CzWINDOWEDFIR::lut[WFIR_LUTLEN*WFIR_WIDTH];
CzWINDOWEDFIR::CzWINDOWEDFIR()
{ int _LPcl;
float _LPcllen = (float)(1L<<WFIR_FRACBITS); // number of precalculated lines for 0..1 (-1..0)
float _LNorm = 1.0f / (float)(2.0f * _LPcllen);
float _LCut = WFIR_CUTOFF;
float _LScale = (float)WFIR_QUANTSCALE;
float _LGain,_LCoefs[WFIR_WIDTH];
for( _LPcl=0;_LPcl<WFIR_LUTLEN;_LPcl++ )
{
float _LOfs = ((float)_LPcl-_LPcllen)*_LNorm;
int _LCc,_LIdx = _LPcl<<WFIR_LOG2WIDTH;
for( _LCc=0,_LGain=0.0f;_LCc<WFIR_WIDTH;_LCc++ )
{ _LGain += (_LCoefs[_LCc] = coef( _LCc, _LOfs, _LCut, WFIR_WIDTH, WFIR_TYPE ));
}
_LGain = 1.0f/_LGain;
for( _LCc=0;_LCc<WFIR_WIDTH;_LCc++ )
{ float _LCoef = (float)floor( 0.5 + _LScale*_LCoefs[_LCc]*_LGain );
lut[_LIdx+_LCc] = (signed short)( (_LCoef<-_LScale)?-_LScale:((_LCoef>_LScale)?_LScale:_LCoef) );
}
}
}
CzWINDOWEDFIR::~CzWINDOWEDFIR()
{ // nothing todo
}
CzWINDOWEDFIR sfir;
// extern "C" signed short *fir_lut = &CzWINDOWEDFIR::lut[0];
#define lut(a) CzWINDOWEDFIR::lut[a]
int main()
{
FILE *f;
int i;
f = fopen("fir_table.h","w");
fprintf(f,"static __int64 fir_lut[%d] = {\n",WFIR_LUTLEN * 2);
for (i=0;i<(WFIR_LUTLEN*WFIR_WIDTH);i+=WFIR_WIDTH)
{
fprintf(f,"\t0x%.4hx%.4hx%.4hx%.4hx, 0x%.4hx%.4hx%.4hx%.4hx%s",
lut(i+3), lut(i+2), lut(i+1), lut(i),
lut(i+7), lut(i+6), lut(i+5), lut(i+4),
(i<((WFIR_LUTLEN-1)*WFIR_WIDTH)) ? ",\n" : "\n};\n");
}
fclose(f);
return(0);
}
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