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347 lines
12 KiB
C
347 lines
12 KiB
C
/*
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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 Libav.
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*
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* Libav 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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* Libav 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 Libav; 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
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* different IIR filters implementation
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*/
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#include "iirfilter.h"
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#include <math.h>
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#include "libavutil/common.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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static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
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enum IIRFilterMode filt_mode,
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int order, float cutoff_ratio,
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float stopband)
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{
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int i, j;
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double wa;
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double p[MAXORDER + 1][2];
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if (filt_mode != FF_FILTER_MODE_LOWPASS) {
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av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
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"low-pass filter mode\n");
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return -1;
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}
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if (order & 1) {
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av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
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"even filter orders\n");
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return -1;
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}
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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][0] = 1.0;
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p[0][1] = 0.0;
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for(i = 1; i <= order; i++)
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p[i][0] = p[i][1] = 0.0;
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for(i = 0; i < order; i++){
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double zp[2];
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double th = (i + (order >> 1) + 0.5) * M_PI / order;
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double a_re, a_im, c_re, c_im;
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zp[0] = cos(th) * wa;
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zp[1] = sin(th) * wa;
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a_re = zp[0] + 2.0;
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c_re = zp[0] - 2.0;
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a_im =
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c_im = zp[1];
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zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
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zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
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for(j = order; j >= 1; j--)
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{
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a_re = p[j][0];
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a_im = p[j][1];
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p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
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p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
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}
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a_re = p[0][0]*zp[0] - p[0][1]*zp[1];
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p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
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p[0][0] = a_re;
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}
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c->gain = p[order][0];
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for(i = 0; i < order; i++){
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c->gain += p[i][0];
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c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
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(p[order][0] * p[order][0] + p[order][1] * p[order][1]);
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}
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c->gain /= 1 << order;
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return 0;
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}
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static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
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enum IIRFilterMode filt_mode, int order,
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float cutoff_ratio, float stopband)
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{
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double cos_w0, sin_w0;
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double a0, x0, x1;
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if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
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filt_mode != FF_FILTER_MODE_LOWPASS) {
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av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
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"high-pass and low-pass filter modes\n");
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return -1;
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}
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if (order != 2) {
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av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
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return -1;
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}
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cos_w0 = cos(M_PI * cutoff_ratio);
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sin_w0 = sin(M_PI * cutoff_ratio);
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a0 = 1.0 + (sin_w0 / 2.0);
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if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
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c->gain = ((1.0 + cos_w0) / 2.0) / a0;
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x0 = ((1.0 + cos_w0) / 2.0) / a0;
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x1 = (-(1.0 + cos_w0)) / a0;
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} else { // FF_FILTER_MODE_LOWPASS
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c->gain = ((1.0 - cos_w0) / 2.0) / a0;
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x0 = ((1.0 - cos_w0) / 2.0) / a0;
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x1 = (1.0 - cos_w0) / a0;
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}
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c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0;
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c->cy[1] = (2.0 * cos_w0) / a0;
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// divide by gain to make the x coeffs integers.
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// during filtering, the delay state will include the gain multiplication
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c->cx[0] = lrintf(x0 / c->gain);
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c->cx[1] = lrintf(x1 / c->gain);
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return 0;
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}
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av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
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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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FFIIRFilterCoeffs *c;
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int ret = 0;
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if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
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return NULL;
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FF_ALLOCZ_OR_GOTO(avc, c, sizeof(FFIIRFilterCoeffs),
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init_fail);
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FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
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init_fail);
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FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
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init_fail);
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c->order = order;
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switch (filt_type) {
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case FF_FILTER_TYPE_BUTTERWORTH:
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ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
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stopband);
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break;
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case FF_FILTER_TYPE_BIQUAD:
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ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
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stopband);
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break;
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default:
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av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
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goto init_fail;
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}
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if (!ret)
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return c;
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init_fail:
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ff_iir_filter_free_coeffs(c);
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return NULL;
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}
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av_cold 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 CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
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#define CONV_FLT(dest, source) dest = source;
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#define FILTER_BW_O4_1(i0, i1, i2, i3, fmt) \
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in = *src0 * 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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CONV_##fmt(*dst0, res) \
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s->x[i0] = in; \
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src0 += sstep; \
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dst0 += dstep;
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#define FILTER_BW_O4(type, fmt) { \
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int i; \
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const type *src0 = src; \
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type *dst0 = dst; \
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for (i = 0; i < size; i += 4) { \
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float in, res; \
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FILTER_BW_O4_1(0, 1, 2, 3, fmt); \
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FILTER_BW_O4_1(1, 2, 3, 0, fmt); \
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FILTER_BW_O4_1(2, 3, 0, 1, fmt); \
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FILTER_BW_O4_1(3, 0, 1, 2, fmt); \
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} \
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}
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#define FILTER_DIRECT_FORM_II(type, fmt) { \
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int i; \
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const type *src0 = src; \
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type *dst0 = dst; \
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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 = *src0 * 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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CONV_##fmt(*dst0, res) \
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s->x[c->order - 1] = in; \
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src0 += sstep; \
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dst0 += dstep; \
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} \
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}
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#define FILTER_O2(type, fmt) { \
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int i; \
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const type *src0 = src; \
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type *dst0 = dst; \
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for (i = 0; i < size; i++) { \
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float in = *src0 * c->gain + \
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s->x[0] * c->cy[0] + \
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s->x[1] * c->cy[1]; \
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CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1]) \
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s->x[0] = s->x[1]; \
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s->x[1] = in; \
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src0 += sstep; \
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dst0 += dstep; \
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} \
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}
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void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
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struct FFIIRFilterState *s, int size,
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const int16_t *src, int sstep, int16_t *dst, int dstep)
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{
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if (c->order == 2) {
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FILTER_O2(int16_t, S16)
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} else if (c->order == 4) {
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FILTER_BW_O4(int16_t, S16)
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} else {
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FILTER_DIRECT_FORM_II(int16_t, S16)
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}
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}
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void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
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struct FFIIRFilterState *s, int size,
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const float *src, int sstep, float *dst, int dstep)
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{
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if (c->order == 2) {
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FILTER_O2(float, FLT)
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} else if (c->order == 4) {
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FILTER_BW_O4(float, FLT)
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} else {
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FILTER_DIRECT_FORM_II(float, FLT)
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}
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}
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av_cold 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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av_cold 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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#ifdef TEST
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#undef printf
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#include <stdio.h>
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#define FILT_ORDER 4
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#define SIZE 1024
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int main(void)
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{
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struct FFIIRFilterCoeffs *fcoeffs = NULL;
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struct FFIIRFilterState *fstate = NULL;
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float cutoff_coeff = 0.4;
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int16_t x[SIZE], y[SIZE];
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int i;
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fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH,
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FF_FILTER_MODE_LOWPASS, FILT_ORDER,
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cutoff_coeff, 0.0, 0.0);
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fstate = ff_iir_filter_init_state(FILT_ORDER);
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for (i = 0; i < SIZE; i++) {
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x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
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}
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ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
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for (i = 0; i < SIZE; i++)
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printf("%6d %6d\n", x[i], y[i]);
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ff_iir_filter_free_coeffs(fcoeffs);
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ff_iir_filter_free_state(fstate);
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return 0;
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}
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#endif /* TEST */
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