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