kopia lustrzana https://github.com/xaelsouth/rtl-wmbus
81 wiersze
2.3 KiB
C
81 wiersze
2.3 KiB
C
|
#ifndef IIR_H
|
||
|
#define IIR_H
|
||
|
|
||
|
/*-
|
||
|
* Copyright (c) 2017 <xael.south@yandex.com>
|
||
|
*
|
||
|
* Redistribution and use in source and binary forms, with or without
|
||
|
* modification, are permitted provided that the following conditions
|
||
|
* are met:
|
||
|
* 1. Redistributions of source code must retain the above copyright
|
||
|
* notice, this list of conditions and the following disclaimer.
|
||
|
* 2. Redistributions in binary form must reproduce the above copyright
|
||
|
* notice, this list of conditions and the following disclaimer in the
|
||
|
* documentation and/or other materials provided with the distribution.
|
||
|
*
|
||
|
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
||
|
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
||
|
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
||
|
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
||
|
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
||
|
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
||
|
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
||
|
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
||
|
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
||
|
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
||
|
* SUCH DAMAGE.
|
||
|
*/
|
||
|
|
||
|
/*
|
||
|
* Implementation of Infinite Response Filter.
|
||
|
*/
|
||
|
|
||
|
#include <stdint.h>
|
||
|
#include <stddef.h>
|
||
|
|
||
|
typedef struct
|
||
|
{
|
||
|
const size_t sections;
|
||
|
|
||
|
const float gain;
|
||
|
const float *const b; // 3 coeff
|
||
|
const float *const a; // 3 coeff, first of these is assumed to be 1
|
||
|
|
||
|
float *hist; // 3 taps
|
||
|
} IIRF_FILTER;
|
||
|
|
||
|
float iirf(float sample, IIRF_FILTER *filter);
|
||
|
|
||
|
float iirf(float sample, IIRF_FILTER *filter)
|
||
|
{
|
||
|
float *hist;
|
||
|
const float *a, *b;
|
||
|
size_t i;
|
||
|
|
||
|
// sample will be "y"
|
||
|
|
||
|
for (i = 0; i < filter->sections; i++)
|
||
|
{
|
||
|
a = filter->a + 3 * i;
|
||
|
b = filter->b + 3 * i;
|
||
|
hist = filter->hist + 3 * i;
|
||
|
|
||
|
#if 0
|
||
|
hist[0] = -sample;
|
||
|
hist[0] = -(a[0]*hist[0] + a[1]*hist[1] + a[2]*hist[2]);
|
||
|
#else
|
||
|
hist[0] = sample - (a[1]*hist[1] + a[2]*hist[2]);
|
||
|
#endif
|
||
|
sample = b[0]*hist[0] + b[1]*hist[1] + b[2]*hist[2];
|
||
|
hist[2] = hist[1];
|
||
|
hist[1] = hist[0];
|
||
|
}
|
||
|
|
||
|
sample *= filter->gain;
|
||
|
|
||
|
return sample;
|
||
|
}
|
||
|
|
||
|
#endif /* IIR_H */
|
||
|
|