snd_flt.cpp
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/*
* This source code is public domain.
*
* Authors: Olivier Lapicque <olivierl@jps.net>
*/
#include "stdafx.h"
#include "sndfile.h"
// AWE32: cutoff = reg[0-255] * 31.25 + 100 -> [100Hz-8060Hz]
// EMU10K1 docs: cutoff = reg[0-127]*62+100
#define FILTER_PRECISION 8192
#ifndef NO_FILTER
#ifdef MSC_VER
#define _ASM_MATH
#endif
#ifdef _ASM_MATH
// pow(a,b) returns a^^b -> 2^^(b.log2(a))
static float pow(float a, float b)
{
long tmpint;
float result;
_asm {
fld b // Load b
fld a // Load a
fyl2x // ST(0) = b.log2(a)
fist tmpint // Store integer exponent
fisub tmpint // ST(0) = -1 <= (b*log2(a)) <= 1
f2xm1 // ST(0) = 2^(x)-1
fild tmpint // load integer exponent
fld1 // Load 1
fscale // ST(0) = 2^ST(1)
fstp ST(1) // Remove the integer from the stack
fmul ST(1), ST(0) // multiply with fractional part
faddp ST(1), ST(0) // add integer_part
fstp result // Store the result
}
return result;
}
#else
#include <math.h>
#endif // _ASM_MATH
DWORD CSoundFile::CutOffToFrequency(UINT nCutOff, int flt_modifier) const
//-----------------------------------------------------------------------
{
float Fc;
if (m_dwSongFlags & SONG_EXFILTERRANGE)
Fc = 110.0f * pow(2.0f, 0.25f + ((float)(nCutOff*(flt_modifier+256)))/(21.0f*512.0f));
else
Fc = 110.0f * pow(2.0f, 0.25f + ((float)(nCutOff*(flt_modifier+256)))/(24.0f*512.0f));
LONG freq = (LONG)Fc;
if (freq < 120) return 120;
if (freq > 10000) return 10000;
if (freq*2 > (LONG)gdwMixingFreq) freq = gdwMixingFreq>>1;
return (DWORD)freq;
}
// Simple 2-poles resonant filter
void CSoundFile::SetupChannelFilter(MODCHANNEL *pChn, BOOL bReset, int flt_modifier) const
//----------------------------------------------------------------------------------------
{
float fc = (float)CutOffToFrequency(pChn->nCutOff, flt_modifier);
float fs = (float)gdwMixingFreq;
float fg, fb0, fb1;
fc *= (float)(2.0*3.14159265358/fs);
float dmpfac = pow(10.0f, -((24.0f / 128.0f)*(float)pChn->nResonance) / 20.0f);
float d = (1.0f-2.0f*dmpfac)* fc;
if (d>2.0) d = 2.0;
d = (2.0f*dmpfac - d)/fc;
float e = pow(1.0f/fc,2.0f);
fg=1/(1+d+e);
fb0=(d+e+e)/(1+d+e);
fb1=-e/(1+d+e);
pChn->nFilter_A0 = (int)(fg * FILTER_PRECISION);
pChn->nFilter_B0 = (int)(fb0 * FILTER_PRECISION);
pChn->nFilter_B1 = (int)(fb1 * FILTER_PRECISION);
if (bReset)
{
pChn->nFilter_Y1 = pChn->nFilter_Y2 = 0;
pChn->nFilter_Y3 = pChn->nFilter_Y4 = 0;
}
pChn->dwFlags |= CHN_FILTER;
}
#endif // NO_FILTER