yading@10: /*
yading@10:  * IIR filter
yading@10:  * Copyright (c) 2008 Konstantin Shishkov
yading@10:  *
yading@10:  * This file is part of FFmpeg.
yading@10:  *
yading@10:  * FFmpeg is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * FFmpeg is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with FFmpeg; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: /**
yading@10:  * @file
yading@10:  * different IIR filters implementation
yading@10:  */
yading@10: 
yading@10: #include "iirfilter.h"
yading@10: #include <math.h>
yading@10: #include "libavutil/common.h"
yading@10: 
yading@10: /**
yading@10:  * IIR filter global parameters
yading@10:  */
yading@10: typedef struct FFIIRFilterCoeffs{
yading@10:     int   order;
yading@10:     float gain;
yading@10:     int   *cx;
yading@10:     float *cy;
yading@10: }FFIIRFilterCoeffs;
yading@10: 
yading@10: /**
yading@10:  * IIR filter state
yading@10:  */
yading@10: typedef struct FFIIRFilterState{
yading@10:     float x[1];
yading@10: }FFIIRFilterState;
yading@10: 
yading@10: /// maximum supported filter order
yading@10: #define MAXORDER 30
yading@10: 
yading@10: static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
yading@10:                                    enum IIRFilterMode filt_mode,
yading@10:                                    int order, float cutoff_ratio,
yading@10:                                    float stopband)
yading@10: {
yading@10:     int i, j;
yading@10:     double wa;
yading@10:     double p[MAXORDER + 1][2];
yading@10: 
yading@10:     if (filt_mode != FF_FILTER_MODE_LOWPASS) {
yading@10:         av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
yading@10:                "low-pass filter mode\n");
yading@10:         return -1;
yading@10:     }
yading@10:     if (order & 1) {
yading@10:         av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
yading@10:                "even filter orders\n");
yading@10:         return -1;
yading@10:     }
yading@10: 
yading@10:     wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
yading@10: 
yading@10:     c->cx[0] = 1;
yading@10:     for(i = 1; i < (order >> 1) + 1; i++)
yading@10:         c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
yading@10: 
yading@10:     p[0][0] = 1.0;
yading@10:     p[0][1] = 0.0;
yading@10:     for(i = 1; i <= order; i++)
yading@10:         p[i][0] = p[i][1] = 0.0;
yading@10:     for(i = 0; i < order; i++){
yading@10:         double zp[2];
yading@10:         double th = (i + (order >> 1) + 0.5) * M_PI / order;
yading@10:         double a_re, a_im, c_re, c_im;
yading@10:         zp[0] = cos(th) * wa;
yading@10:         zp[1] = sin(th) * wa;
yading@10:         a_re = zp[0] + 2.0;
yading@10:         c_re = zp[0] - 2.0;
yading@10:         a_im =
yading@10:         c_im = zp[1];
yading@10:         zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
yading@10:         zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
yading@10: 
yading@10:         for(j = order; j >= 1; j--)
yading@10:         {
yading@10:             a_re = p[j][0];
yading@10:             a_im = p[j][1];
yading@10:             p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
yading@10:             p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
yading@10:         }
yading@10:         a_re    = p[0][0]*zp[0] - p[0][1]*zp[1];
yading@10:         p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
yading@10:         p[0][0] = a_re;
yading@10:     }
yading@10:     c->gain = p[order][0];
yading@10:     for(i = 0; i < order; i++){
yading@10:         c->gain += p[i][0];
yading@10:         c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
yading@10:                    (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
yading@10:     }
yading@10:     c->gain /= 1 << order;
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
yading@10:                               enum IIRFilterMode filt_mode, int order,
yading@10:                               float cutoff_ratio, float stopband)
yading@10: {
yading@10:     double cos_w0, sin_w0;
yading@10:     double a0, x0, x1;
yading@10: 
yading@10:     if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
yading@10:         filt_mode != FF_FILTER_MODE_LOWPASS) {
yading@10:         av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
yading@10:                "high-pass and low-pass filter modes\n");
yading@10:         return -1;
yading@10:     }
yading@10:     if (order != 2) {
yading@10:         av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
yading@10:         return -1;
yading@10:     }
yading@10: 
yading@10:     cos_w0 = cos(M_PI * cutoff_ratio);
yading@10:     sin_w0 = sin(M_PI * cutoff_ratio);
yading@10: 
yading@10:     a0 = 1.0 + (sin_w0 / 2.0);
yading@10: 
yading@10:     if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
yading@10:         c->gain  =  ((1.0 + cos_w0) / 2.0)  / a0;
yading@10:         x0       =  ((1.0 + cos_w0) / 2.0)  / a0;
yading@10:         x1       = (-(1.0 + cos_w0))        / a0;
yading@10:     } else { // FF_FILTER_MODE_LOWPASS
yading@10:         c->gain  =  ((1.0 - cos_w0) / 2.0)  / a0;
yading@10:         x0       =  ((1.0 - cos_w0) / 2.0)  / a0;
yading@10:         x1       =   (1.0 - cos_w0)         / a0;
yading@10:     }
yading@10:     c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0;
yading@10:     c->cy[1] =  (2.0 *  cos_w0)        / a0;
yading@10: 
yading@10:     // divide by gain to make the x coeffs integers.
yading@10:     // during filtering, the delay state will include the gain multiplication
yading@10:     c->cx[0] = lrintf(x0 / c->gain);
yading@10:     c->cx[1] = lrintf(x1 / c->gain);
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
yading@10:                                                 enum IIRFilterType filt_type,
yading@10:                                                 enum IIRFilterMode filt_mode,
yading@10:                                                 int order, float cutoff_ratio,
yading@10:                                                 float stopband, float ripple)
yading@10: {
yading@10:     FFIIRFilterCoeffs *c;
yading@10:     int ret = 0;
yading@10: 
yading@10:     if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
yading@10:         return NULL;
yading@10: 
yading@10:     FF_ALLOCZ_OR_GOTO(avc, c,     sizeof(FFIIRFilterCoeffs),
yading@10:                       init_fail);
yading@10:     FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
yading@10:                       init_fail);
yading@10:     FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
yading@10:                       init_fail);
yading@10:     c->order = order;
yading@10: 
yading@10:     switch (filt_type) {
yading@10:     case FF_FILTER_TYPE_BUTTERWORTH:
yading@10:         ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
yading@10:                                       stopband);
yading@10:         break;
yading@10:     case FF_FILTER_TYPE_BIQUAD:
yading@10:         ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
yading@10:                                  stopband);
yading@10:         break;
yading@10:     default:
yading@10:         av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
yading@10:         goto init_fail;
yading@10:     }
yading@10: 
yading@10:     if (!ret)
yading@10:         return c;
yading@10: 
yading@10: init_fail:
yading@10:     ff_iir_filter_free_coeffs(c);
yading@10:     return NULL;
yading@10: }
yading@10: 
yading@10: av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
yading@10: {
yading@10:     FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
yading@10:     return s;
yading@10: }
yading@10: 
yading@10: #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
yading@10: 
yading@10: #define CONV_FLT(dest, source) dest = source;
yading@10: 
yading@10: #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt)         \
yading@10:     in = *src0 * c->gain                            \
yading@10:          + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]    \
yading@10:          + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3];   \
yading@10:     res =  (s->x[i0] + in      )*1                  \
yading@10:          + (s->x[i1] + s->x[i3])*4                  \
yading@10:          +  s->x[i2]            *6;                 \
yading@10:     CONV_##fmt(*dst0, res)                          \
yading@10:     s->x[i0] = in;                                  \
yading@10:     src0 += sstep;                                  \
yading@10:     dst0 += dstep;
yading@10: 
yading@10: #define FILTER_BW_O4(type, fmt) {           \
yading@10:     int i;                                  \
yading@10:     const type *src0 = src;                 \
yading@10:     type       *dst0 = dst;                 \
yading@10:     for (i = 0; i < size; i += 4) {         \
yading@10:         float in, res;                      \
yading@10:         FILTER_BW_O4_1(0, 1, 2, 3, fmt);    \
yading@10:         FILTER_BW_O4_1(1, 2, 3, 0, fmt);    \
yading@10:         FILTER_BW_O4_1(2, 3, 0, 1, fmt);    \
yading@10:         FILTER_BW_O4_1(3, 0, 1, 2, fmt);    \
yading@10:     }                                       \
yading@10: }
yading@10: 
yading@10: #define FILTER_DIRECT_FORM_II(type, fmt) {                                  \
yading@10:     int i;                                                                  \
yading@10:     const type *src0 = src;                                                 \
yading@10:     type       *dst0 = dst;                                                 \
yading@10:     for (i = 0; i < size; i++) {                                            \
yading@10:         int j;                                                              \
yading@10:         float in, res;                                                      \
yading@10:         in = *src0 * c->gain;                                               \
yading@10:         for(j = 0; j < c->order; j++)                                       \
yading@10:             in += c->cy[j] * s->x[j];                                       \
yading@10:         res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];    \
yading@10:         for(j = 1; j < c->order >> 1; j++)                                  \
yading@10:             res += (s->x[j] + s->x[c->order - j]) * c->cx[j];               \
yading@10:         for(j = 0; j < c->order - 1; j++)                                   \
yading@10:             s->x[j] = s->x[j + 1];                                          \
yading@10:         CONV_##fmt(*dst0, res)                                              \
yading@10:         s->x[c->order - 1] = in;                                            \
yading@10:         src0 += sstep;                                                      \
yading@10:         dst0 += dstep;                                                      \
yading@10:     }                                                                       \
yading@10: }
yading@10: 
yading@10: #define FILTER_O2(type, fmt) {                                              \
yading@10:     int i;                                                                  \
yading@10:     const type *src0 = src;                                                 \
yading@10:     type       *dst0 = dst;                                                 \
yading@10:     for (i = 0; i < size; i++) {                                            \
yading@10:         float in = *src0   * c->gain  +                                     \
yading@10:                    s->x[0] * c->cy[0] +                                     \
yading@10:                    s->x[1] * c->cy[1];                                      \
yading@10:         CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1])                \
yading@10:         s->x[0] = s->x[1];                                                  \
yading@10:         s->x[1] = in;                                                       \
yading@10:         src0 += sstep;                                                      \
yading@10:         dst0 += dstep;                                                      \
yading@10:     }                                                                       \
yading@10: }
yading@10: 
yading@10: void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
yading@10:                    struct FFIIRFilterState *s, int size,
yading@10:                    const int16_t *src, int sstep, int16_t *dst, int dstep)
yading@10: {
yading@10:     if (c->order == 2) {
yading@10:         FILTER_O2(int16_t, S16)
yading@10:     } else if (c->order == 4) {
yading@10:         FILTER_BW_O4(int16_t, S16)
yading@10:     } else {
yading@10:         FILTER_DIRECT_FORM_II(int16_t, S16)
yading@10:     }
yading@10: }
yading@10: 
yading@10: void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
yading@10:                        struct FFIIRFilterState *s, int size,
yading@10:                        const float *src, int sstep, float *dst, int dstep)
yading@10: {
yading@10:     if (c->order == 2) {
yading@10:         FILTER_O2(float, FLT)
yading@10:     } else if (c->order == 4) {
yading@10:         FILTER_BW_O4(float, FLT)
yading@10:     } else {
yading@10:         FILTER_DIRECT_FORM_II(float, FLT)
yading@10:     }
yading@10: }
yading@10: 
yading@10: av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
yading@10: {
yading@10:     av_free(state);
yading@10: }
yading@10: 
yading@10: av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
yading@10: {
yading@10:     if(coeffs){
yading@10:         av_free(coeffs->cx);
yading@10:         av_free(coeffs->cy);
yading@10:     }
yading@10:     av_free(coeffs);
yading@10: }
yading@10: 
yading@10: void ff_iir_filter_init(FFIIRFilterContext *f) {
yading@10:     f->filter_flt = ff_iir_filter_flt;
yading@10: 
yading@10:     if (HAVE_MIPSFPU)
yading@10:         ff_iir_filter_init_mips(f);
yading@10: }
yading@10: 
yading@10: #ifdef TEST
yading@10: #include <stdio.h>
yading@10: 
yading@10: #define FILT_ORDER 4
yading@10: #define SIZE 1024
yading@10: int main(void)
yading@10: {
yading@10:     struct FFIIRFilterCoeffs *fcoeffs = NULL;
yading@10:     struct FFIIRFilterState  *fstate  = NULL;
yading@10:     float cutoff_coeff = 0.4;
yading@10:     int16_t x[SIZE], y[SIZE];
yading@10:     int i;
yading@10: 
yading@10:     fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH,
yading@10:                                         FF_FILTER_MODE_LOWPASS, FILT_ORDER,
yading@10:                                         cutoff_coeff, 0.0, 0.0);
yading@10:     fstate  = ff_iir_filter_init_state(FILT_ORDER);
yading@10: 
yading@10:     for (i = 0; i < SIZE; i++) {
yading@10:         x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
yading@10:     }
yading@10: 
yading@10:     ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
yading@10: 
yading@10:     for (i = 0; i < SIZE; i++)
yading@10:         printf("%6d %6d\n", x[i], y[i]);
yading@10: 
yading@10:     ff_iir_filter_free_coeffs(fcoeffs);
yading@10:     ff_iir_filter_free_state(fstate);
yading@10:     return 0;
yading@10: }
yading@10: #endif /* TEST */