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