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#ifndef _AL_FILTER_H_
#define _AL_FILTER_H_
#include "AL/al.h"
#include "alu.h"
#ifdef __cplusplus
extern "C" {
#endif
typedef struct {
ALfloat coeff;
#ifndef _MSC_VER
ALfloat history[0];
#else
ALfloat history[1];
#endif
} FILTER;
static __inline ALfloat lpFilter4P(FILTER *iir, ALuint offset, ALfloat input)
{
ALfloat *history = &iir->history[offset];
ALfloat a = iir->coeff;
ALfloat output = input;
output = output + (history[0]-output)*a;
history[0] = output;
output = output + (history[1]-output)*a;
history[1] = output;
output = output + (history[2]-output)*a;
history[2] = output;
output = output + (history[3]-output)*a;
history[3] = output;
return output;
}
static __inline ALfloat lpFilter2P(FILTER *iir, ALuint offset, ALfloat input)
{
ALfloat *history = &iir->history[offset];
ALfloat a = iir->coeff;
ALfloat output = input;
output = output + (history[0]-output)*a;
history[0] = output;
output = output + (history[1]-output)*a;
history[1] = output;
return output;
}
static __inline ALfloat lpFilter1P(FILTER *iir, ALuint offset, ALfloat input)
{
ALfloat *history = &iir->history[offset];
ALfloat a = iir->coeff;
ALfloat output = input;
output = output + (history[0]-output)*a;
history[0] = output;
return output;
}
/* Calculates the low-pass filter coefficient given the pre-scaled gain and
* cos(w) value. Note that g should be pre-scaled (sqr(gain) for one-pole,
* sqrt(gain) for four-pole, etc) */
static __inline ALfloat lpCoeffCalc(ALfloat g, ALfloat cw)
{
ALfloat a = 0.0f;
/* Be careful with gains < 0.01, as that causes the coefficient
* head towards 1, which will flatten the signal */
g = __max(g, 0.01f);
if(g < 0.9999f) /* 1-epsilon */
a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) /
(1 - g);
return a;
}
typedef struct ALfilter
{
// Filter type (AL_FILTER_NULL, ...)
ALenum type;
ALfloat Gain;
ALfloat GainHF;
// Index to itself
ALuint filter;
struct ALfilter *next;
} ALfilter;
ALvoid ReleaseALFilters(ALCdevice *device);
#ifdef __cplusplus
}
#endif
#endif
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