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/*
* WindowedFIR.h
* -------------
* Purpose: FIR resampling code
* Notes : (currently none)
* Authors: OpenMPT Devs
* ModPlug-XMMS Devs
* The OpenMPT source code is released under the BSD license. Read LICENSE for more details.
*/
#pragma once
#include "BuildSettings.h"
#include "Mixer.h"
OPENMPT_NAMESPACE_BEGIN
/*
------------------------------------------------------------------------------------------------
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.
------------------------------------------------------------------------------------------------
*/
#ifdef MPT_INTMIXER
// quantizer scale of window coefs - only required for integer mixing
#define WFIR_QUANTBITS 15
#define WFIR_QUANTSCALE double(1L<<WFIR_QUANTBITS)
#define WFIR_8SHIFT (WFIR_QUANTBITS-8)
#define WFIR_16BITSHIFT (WFIR_QUANTBITS)
typedef int16 WFIR_TYPE;
#else
typedef mixsample_t WFIR_TYPE;
#endif // INTMIXER
// log2(number)-1 of precalculated taps range is [4..12]
#define WFIR_FRACBITS 12 //10
#define WFIR_LUTLEN ((1L<<(WFIR_FRACBITS+1))+1)
// number of samples in window
#define WFIR_LOG2WIDTH 3
#define WFIR_WIDTH (1L<<WFIR_LOG2WIDTH)
// cutoff (1.0 == pi/2)
// wfir type
enum WFIRType
{
WFIR_HANN = 0, // Hann
WFIR_HAMMING = 1, // Hamming
WFIR_BLACKMANEXACT = 2, // Blackman Exact
WFIR_BLACKMAN3T61 = 3, // Blackman 3-Tap 61
WFIR_BLACKMAN3T67 = 4, // Blackman 3-Tap 67
WFIR_BLACKMAN4T92 = 5, // Blackman-Harris
WFIR_BLACKMAN4T74 = 6, // Blackman 4-Tap 74
WFIR_KAISER4T = 7, // Kaiser a=7.5
};
// wfir help
#define M_zPI 3.1415926535897932384626433832795
#define M_zEPS 1e-8
// fir interpolation
#define WFIR_FRACSHIFT (16-(WFIR_FRACBITS+1+WFIR_LOG2WIDTH))
#define WFIR_FRACMASK ((((1L<<(17-WFIR_FRACSHIFT))-1)&~((1L<<WFIR_LOG2WIDTH)-1)))
#define WFIR_FRACHALVE (1L<<(16-(WFIR_FRACBITS+2)))
class CWindowedFIR
{
private:
double coef(int,double,double,int,int);
public:
void InitTable(double WFIRCutoff, uint8 WFIRType);
WFIR_TYPE lut[WFIR_LUTLEN*WFIR_WIDTH];
};
OPENMPT_NAMESPACE_END