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https://github.com/FFmpeg/FFmpeg.git
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165 lines
4.7 KiB
C
165 lines
4.7 KiB
C
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/*
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* IIR filter
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* Copyright (c) 2008 Konstantin Shishkov
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file iirfilter.c
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* different IIR filters implementation
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*/
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#include "iirfilter.h"
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#include <complex.h>
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#include <math.h>
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/**
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* IIR filter global parameters
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*/
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typedef struct FFIIRFilterCoeffs{
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int order;
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float gain;
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int *cx;
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float *cy;
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}FFIIRFilterCoeffs;
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/**
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* IIR filter state
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*/
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typedef struct FFIIRFilterState{
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float x[1];
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}FFIIRFilterState;
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/// maximum supported filter order
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#define MAXORDER 30
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struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
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enum IIRFilterMode filt_mode,
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int order, float cutoff_ratio,
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float stopband, float ripple)
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{
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int i, j, size;
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FFIIRFilterCoeffs *c;
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double wa;
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complex p[MAXORDER + 1];
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if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
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return NULL;
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if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0)
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return NULL;
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c = av_malloc(sizeof(FFIIRFilterCoeffs));
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c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1));
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c->cy = av_malloc(sizeof(c->cy[0]) * order);
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c->order = order;
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wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
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c->cx[0] = 1;
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for(i = 1; i < (order >> 1) + 1; i++)
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c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
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p[0] = 1.0;
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for(i = 1; i <= order; i++)
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p[i] = 0.0;
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for(i = 0; i < order; i++){
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complex zp;
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double th = (i + (order >> 1) + 0.5) * M_PI / order;
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zp = cexp(I*th) * wa;
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zp = (zp + 2.0) / (zp - 2.0);
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for(j = order; j >= 1; j--)
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p[j] = zp*p[j] + p[j - 1];
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p[0] *= zp;
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}
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c->gain = creal(p[order]);
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for(i = 0; i < order; i++){
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c->gain += creal(p[i]);
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c->cy[i] = creal(-p[i] / p[order]);
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}
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c->gain /= 1 << order;
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return c;
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}
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struct FFIIRFilterState* ff_iir_filter_init_state(int order)
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{
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FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
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return s;
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}
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#define FILTER(i0, i1, i2, i3) \
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in = *src * c->gain \
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+ c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \
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+ c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
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res = (s->x[i0] + in )*1 \
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+ (s->x[i1] + s->x[i3])*4 \
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+ s->x[i2] *6; \
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*dst = av_clip_int16(lrintf(res)); \
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s->x[i0] = in; \
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src += sstep; \
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dst += dstep; \
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void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep)
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{
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int i;
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if(c->order == 4){
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for(i = 0; i < size; i += 4){
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float in, res;
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FILTER(0, 1, 2, 3);
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FILTER(1, 2, 3, 0);
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FILTER(2, 3, 0, 1);
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FILTER(3, 0, 1, 2);
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}
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}else{
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for(i = 0; i < size; i++){
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int j;
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float in, res;
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in = *src * c->gain;
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for(j = 0; j < c->order; j++)
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in += c->cy[j] * s->x[j];
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res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];
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for(j = 1; j < c->order >> 1; j++)
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res += (s->x[j] + s->x[c->order - j]) * c->cx[j];
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for(j = 0; j < c->order - 1; j++)
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s->x[j] = s->x[j + 1];
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*dst = av_clip_int16(lrintf(res));
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s->x[c->order - 1] = in;
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src += sstep;
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dst += sstep;
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}
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}
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}
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void ff_iir_filter_free_state(struct FFIIRFilterState *state)
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{
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av_free(state);
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}
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void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
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{
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if(coeffs){
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av_free(coeffs->cx);
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av_free(coeffs->cy);
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}
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av_free(coeffs);
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}
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