/*
  * 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 <math.h>

 #include "libavutil/attributes.h"

 #include "libavutil/common.h"

 #include "iirfilter.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 av_cold 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 av_cold 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_coeffsp(&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, ptrdiff_t sstep,
                    int16_t *dst, ptrdiff_t 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, ptrdiff_t sstep,
                        float *dst, ptrdiff_t 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_statep(struct FFIIRFilterState **state)

 {

     av_freep(state);

 }
 

 av_cold void ff_iir_filter_free_coeffsp(struct FFIIRFilterCoeffs **coeffsp)

 {

     struct FFIIRFilterCoeffs *coeffs = *coeffsp;

     if (coeffs) {

         av_freep(&coeffs->cx);
         av_freep(&coeffs->cy);

     }

     av_freep(coeffsp);

 }
 

 void ff_iir_filter_init(FFIIRFilterContext *f) {
     f->filter_flt = ff_iir_filter_flt;
 
     if (HAVE_MIPSFPU)
         ff_iir_filter_init_mips(f);
 }