PeerStreamer

/*

 * 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);

    c->cy[0] /= c->gain;

    c->cy[1] /= 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

#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;

    FILE* fd;

    fcoeffs = ff_iir_filter_init_coeffs(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);

    fd = fopen("in.bin", "w");

    fwrite(x, sizeof(x[0]), SIZE, fd);

    fclose(fd);

    fd = fopen("out.bin", "w");

    fwrite(y, sizeof(y[0]), SIZE, fd);

    fclose(fd);

    ff_iir_filter_free_coeffs(fcoeffs);

    ff_iir_filter_free_state(fstate);

    return 0;

}

#endif /* TEST */