/*
* IIR filter
* Copyright (c) 2008 Konstantin Shishkov
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* different IIR filters implementation
*/
#include "iirfilter.h"
#include <math.h>
/**
* IIR filter global parameters
*/
typedef struct FFIIRFilterCoeffs{
int order;
float gain;
int *cx;
float *cy;
}FFIIRFilterCoeffs;
/**
* IIR filter state
*/
typedef struct FFIIRFilterState{
float x[1];
}FFIIRFilterState;
/// maximum supported filter order
#define MAXORDER 30
static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
enum IIRFilterMode filt_mode,
int order, float cutoff_ratio,
float stopband)
{
int i, j;
double wa;
double p[MAXORDER + 1][2];
if (filt_mode != FF_FILTER_MODE_LOWPASS) {
av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
"low-pass filter mode\n");
return -1;
}
if (order & 1) {
av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
"even filter orders\n");
return -1;
}
wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
c->cx[0] = 1;
for(i = 1; i < (order >> 1) + 1; i++)
c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
p[0][0] = 1.0;
p[0][1] = 0.0;
for(i = 1; i <= order; i++)
p[i][0] = p[i][1] = 0.0;
for(i = 0; i < order; i++){
double zp[2];
double th = (i + (order >> 1) + 0.5) * M_PI / order;
double a_re, a_im, c_re, c_im;
zp[0] = cos(th) * wa;
zp[1] = sin(th) * wa;
a_re = zp[0] + 2.0;
c_re = zp[0] - 2.0;
a_im =
c_im = zp[1];
zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
for(j = order; j >= 1; j--)
{
a_re = p[j][0];
a_im = p[j][1];
p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
}
a_re = p[0][0]*zp[0] - p[0][1]*zp[1];
p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
p[0][0] = a_re;
}
c->gain = p[order][0];
for(i = 0; i < order; i++){
c->gain += p[i][0];
c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
(p[order][0] * p[order][0] + p[order][1] * p[order][1]);
}
c->gain /= 1 << order;
return 0;
}
static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
enum IIRFilterMode filt_mode, int order,
float cutoff_ratio, float stopband)
{
double cos_w0, sin_w0;
double a0, x0, x1;
if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
filt_mode != FF_FILTER_MODE_LOWPASS) {
av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
"high-pass and low-pass filter modes\n");
return -1;
}
if (order != 2) {
av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
return -1;
}
cos_w0 = cos(M_PI * cutoff_ratio);
sin_w0 = sin(M_PI * cutoff_ratio);
a0 = 1.0 + (sin_w0 / 2.0);
if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
c->gain = ((1.0 + cos_w0) / 2.0) / a0;
x0 = ((1.0 + cos_w0) / 2.0) / a0;
x1 = (-(1.0 + cos_w0)) / a0;
} else { // FF_FILTER_MODE_LOWPASS
c->gain = ((1.0 - cos_w0) / 2.0) / a0;
x0 = ((1.0 - cos_w0) / 2.0) / a0;
x1 = (1.0 - cos_w0) / a0;
}
c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0;
c->cy[1] = (2.0 * cos_w0) / a0;
// divide by gain to make the x coeffs integers.
// during filtering, the delay state will include the gain multiplication
c->cx[0] = lrintf(x0 / c->gain);
c->cx[1] = lrintf(x1 / c->gain);
return 0;
}
av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
enum IIRFilterType filt_type,
enum IIRFilterMode filt_mode,
int order, float cutoff_ratio,
float stopband, float ripple)
{
FFIIRFilterCoeffs *c;
int ret = 0;
if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
return NULL;
FF_ALLOCZ_OR_GOTO(avc, c, sizeof(FFIIRFilterCoeffs),
init_fail);
FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
init_fail);
FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
init_fail);
c->order = order;
switch (filt_type) {
case FF_FILTER_TYPE_BUTTERWORTH:
ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
stopband);
break;
case FF_FILTER_TYPE_BIQUAD:
ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
stopband);
break;
default:
av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
goto init_fail;
}
if (!ret)
return c;
init_fail:
ff_iir_filter_free_coeffs(c);
return NULL;
}
av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
{
FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
return s;
}
#define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
#define CONV_FLT(dest, source) dest = source;
#define FILTER_BW_O4_1(i0, i1, i2, i3, fmt) \
in = *src0 * c->gain \
+ c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \
+ c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
res = (s->x[i0] + in )*1 \
+ (s->x[i1] + s->x[i3])*4 \
+ s->x[i2] *6; \
CONV_##fmt(*dst0, res) \
s->x[i0] = in; \
src0 += sstep; \
dst0 += dstep;
#define FILTER_BW_O4(type, fmt) { \
int i; \
const type *src0 = src; \
type *dst0 = dst; \
for (i = 0; i < size; i += 4) { \
float in, res; \
FILTER_BW_O4_1(0, 1, 2, 3, fmt); \
FILTER_BW_O4_1(1, 2, 3, 0, fmt); \
FILTER_BW_O4_1(2, 3, 0, 1, fmt); \
FILTER_BW_O4_1(3, 0, 1, 2, fmt); \
} \
}
#define FILTER_DIRECT_FORM_II(type, fmt) { \
int i; \
const type *src0 = src; \
type *dst0 = dst; \
for (i = 0; i < size; i++) { \
int j; \
float in, res; \
in = *src0 * c->gain; \
for(j = 0; j < c->order; j++) \
in += c->cy[j] * s->x[j]; \
res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; \
for(j = 1; j < c->order >> 1; j++) \
res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; \
for(j = 0; j < c->order - 1; j++) \
s->x[j] = s->x[j + 1]; \
CONV_##fmt(*dst0, res) \
s->x[c->order - 1] = in; \
src0 += sstep; \
dst0 += dstep; \
} \
}
#define FILTER_O2(type, fmt) { \
int i; \
const type *src0 = src; \
type *dst0 = dst; \
for (i = 0; i < size; i++) { \
float in = *src0 * c->gain + \
s->x[0] * c->cy[0] + \
s->x[1] * c->cy[1]; \
CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1]) \
s->x[0] = s->x[1]; \
s->x[1] = in; \
src0 += sstep; \
dst0 += dstep; \
} \
}
void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
struct FFIIRFilterState *s, int size,
const int16_t *src, int sstep, int16_t *dst, int dstep)
{
if (c->order == 2) {
FILTER_O2(int16_t, S16)
} else if (c->order == 4) {
FILTER_BW_O4(int16_t, S16)
} else {
FILTER_DIRECT_FORM_II(int16_t, S16)
}
}
void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
struct FFIIRFilterState *s, int size,
const float *src, int sstep, float *dst, int dstep)
{
if (c->order == 2) {
FILTER_O2(float, FLT)
} else if (c->order == 4) {
FILTER_BW_O4(float, FLT)
} else {
FILTER_DIRECT_FORM_II(float, FLT)
}
}
av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
{
av_free(state);
}
av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
{
if(coeffs){
av_free(coeffs->cx);
av_free(coeffs->cy);
}
av_free(coeffs);
}
#ifdef TEST
#undef printf
#include <stdio.h>
#define FILT_ORDER 4
#define SIZE 1024
int main(void)
{
struct FFIIRFilterCoeffs *fcoeffs = NULL;
struct FFIIRFilterState *fstate = NULL;
float cutoff_coeff = 0.4;
int16_t x[SIZE], y[SIZE];
int i;
fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH,
FF_FILTER_MODE_LOWPASS, FILT_ORDER,
cutoff_coeff, 0.0, 0.0);
fstate = ff_iir_filter_init_state(FILT_ORDER);
for (i = 0; i < SIZE; i++) {
x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
}
ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
for (i = 0; i < SIZE; i++)
printf("%6d %6d\n", x[i], y[i]);
ff_iir_filter_free_coeffs(fcoeffs);
ff_iir_filter_free_state(fstate);
return 0;
}
#endif /* TEST */