text: /*
   * audio resampling
   * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   *
   * 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
   * audio resampling
   * @author Michael Niedermayer <michaelni@gmx.at>
   */
  
  #include "libavutil/avassert.h"
  #include "avcodec.h"
  #include "libavutil/common.h"
  
  #if FF_API_AVCODEC_RESAMPLE
  
  #ifndef CONFIG_RESAMPLE_HP
  #define FILTER_SHIFT 15
  
  #define FELEM int16_t
  #define FELEM2 int32_t
  #define FELEML int64_t
  #define FELEM_MAX INT16_MAX
  #define FELEM_MIN INT16_MIN
  #define WINDOW_TYPE 9
  #elif !defined(CONFIG_RESAMPLE_AUDIOPHILE_KIDDY_MODE)
  #define FILTER_SHIFT 30
  
  #define FELEM int32_t
  #define FELEM2 int64_t
  #define FELEML int64_t
  #define FELEM_MAX INT32_MAX
  #define FELEM_MIN INT32_MIN
  #define WINDOW_TYPE 12
  #else
  #define FILTER_SHIFT 0
  
  #define FELEM double
  #define FELEM2 double
  #define FELEML double
  #define WINDOW_TYPE 24
  #endif
  
  
  typedef struct AVResampleContext{
      const AVClass *av_class;
      FELEM *filter_bank;
      int filter_length;
      int ideal_dst_incr;
      int dst_incr;
      int index;
      int frac;
      int src_incr;
      int compensation_distance;
      int phase_shift;
      int phase_mask;
      int linear;
  }AVResampleContext;
  
  /**
   * 0th order modified bessel function of the first kind.
   */
  static double bessel(double x){
      double v=1;
      double lastv=0;
      double t=1;
      int i;
  
      x= x*x/4;
      for(i=1; v != lastv; i++){
          lastv=v;
          t *= x/(i*i);
          v += t;
      }
      return v;
  }
  
  /**
   * Build a polyphase filterbank.
   * @param factor resampling factor
   * @param scale wanted sum of coefficients for each filter
   * @param type 0->cubic, 1->blackman nuttall windowed sinc, 2..16->kaiser windowed sinc beta=2..16
   * @return 0 on success, negative on error
   */
  static int build_filter(FELEM *filter, double factor, int tap_count, int phase_count, int scale, int type){
      int ph, i;
      double x, y, w;
      double *tab = av_malloc_array(tap_count, sizeof(*tab));
      const int center= (tap_count-1)/2;
  
      if (!tab)
          return AVERROR(ENOMEM);
  
      /* if upsampling, only need to interpolate, no filter */
      if (factor > 1.0)
          factor = 1.0;
  
      for(ph=0;ph<phase_count;ph++) {
          double norm = 0;
          for(i=0;i<tap_count;i++) {
              x = M_PI * ((double)(i - center) - (double)ph / phase_count) * factor;
              if (x == 0) y = 1.0;
              else        y = sin(x) / x;
              switch(type){
              case 0:{
                  const float d= -0.5; //first order derivative = -0.5
                  x = fabs(((double)(i - center) - (double)ph / phase_count) * factor);
                  if(x<1.0) y= 1 - 3*x*x + 2*x*x*x + d*(            -x*x + x*x*x);
                  else      y=                       d*(-4 + 8*x - 5*x*x + x*x*x);
                  break;}
              case 1:
                  w = 2.0*x / (factor*tap_count) + M_PI;
                  y *= 0.3635819 - 0.4891775 * cos(w) + 0.1365995 * cos(2*w) - 0.0106411 * cos(3*w);
                  break;
              default:
                  w = 2.0*x / (factor*tap_count*M_PI);
                  y *= bessel(type*sqrt(FFMAX(1-w*w, 0)));
                  break;
              }
  
              tab[i] = y;
              norm += y;
          }
  
          /* normalize so that an uniform color remains the same */
          for(i=0;i<tap_count;i++) {
  #ifdef CONFIG_RESAMPLE_AUDIOPHILE_KIDDY_MODE
              filter[ph * tap_count + i] = tab[i] / norm;
  #else
              filter[ph * tap_count + i] = av_clip(lrintf(tab[i] * scale / norm), FELEM_MIN, FELEM_MAX);
  #endif
          }
      }
  #if 0
      {
  #define LEN 1024
          int j,k;
          double sine[LEN + tap_count];
          double filtered[LEN];
          double maxff=-2, minff=2, maxsf=-2, minsf=2;
          for(i=0; i<LEN; i++){
              double ss=0, sf=0, ff=0;
              for(j=0; j<LEN+tap_count; j++)
                  sine[j]= cos(i*j*M_PI/LEN);
              for(j=0; j<LEN; j++){
                  double sum=0;
                  ph=0;
                  for(k=0; k<tap_count; k++)
                      sum += filter[ph * tap_count + k] * sine[k+j];
                  filtered[j]= sum / (1<<FILTER_SHIFT);
                  ss+= sine[j + center] * sine[j + center];
                  ff+= filtered[j] * filtered[j];
                  sf+= sine[j + center] * filtered[j];
              }
              ss= sqrt(2*ss/LEN);
              ff= sqrt(2*ff/LEN);
              sf= 2*sf/LEN;
              maxff= FFMAX(maxff, ff);
              minff= FFMIN(minff, ff);
              maxsf= FFMAX(maxsf, sf);
              minsf= FFMIN(minsf, sf);
              if(i%11==0){
                  av_log(NULL, AV_LOG_ERROR, "i:%4d ss:%f ff:%13.6e-%13.6e sf:%13.6e-%13.6e\n", i, ss, maxff, minff, maxsf, minsf);
                  minff=minsf= 2;
                  maxff=maxsf= -2;
              }
          }
      }
  #endif
  
      av_free(tab);
      return 0;
  }
  
  AVResampleContext *av_resample_init(int out_rate, int in_rate, int filter_size, int phase_shift, int linear, double cutoff){
      AVResampleContext *c= av_mallocz(sizeof(AVResampleContext));
      double factor= FFMIN(out_rate * cutoff / in_rate, 1.0);
      int phase_count= 1<<phase_shift;
  
      if (!c)
          return NULL;
  
      c->phase_shift= phase_shift;
      c->phase_mask= phase_count-1;
      c->linear= linear;
  
      c->filter_length= FFMAX((int)ceil(filter_size/factor), 1);
      c->filter_bank= av_mallocz_array(c->filter_length, (phase_count+1)*sizeof(FELEM));
      if (!c->filter_bank)
          goto error;
      if (build_filter(c->filter_bank, factor, c->filter_length, phase_count, 1<<FILTER_SHIFT, WINDOW_TYPE))
          goto error;
      memcpy(&c->filter_bank[c->filter_length*phase_count+1], c->filter_bank, (c->filter_length-1)*sizeof(FELEM));
      c->filter_bank[c->filter_length*phase_count]= c->filter_bank[c->filter_length - 1];
  
      if(!av_reduce(&c->src_incr, &c->dst_incr, out_rate, in_rate * (int64_t)phase_count, INT32_MAX/2))
          goto error;
      c->ideal_dst_incr= c->dst_incr;
  
      c->index= -phase_count*((c->filter_length-1)/2);
  
      return c;
  error:
      av_free(c->filter_bank);
      av_free(c);
      return NULL;
  }
  
  void av_resample_close(AVResampleContext *c){
      av_freep(&c->filter_bank);
      av_freep(&c);
  }
  
  void av_resample_compensate(AVResampleContext *c, int sample_delta, int compensation_distance){
  //    sample_delta += (c->ideal_dst_incr - c->dst_incr)*(int64_t)c->compensation_distance / c->ideal_dst_incr;
      c->compensation_distance= compensation_distance;
      c->dst_incr = c->ideal_dst_incr - c->ideal_dst_incr * (int64_t)sample_delta / compensation_distance;
  }
  
  int av_resample(AVResampleContext *c, short *dst, short *src, int *consumed, int src_size, int dst_size, int update_ctx){
      int dst_index, i;
      int index= c->index;
      int frac= c->frac;
      int dst_incr_frac= c->dst_incr % c->src_incr;
      int dst_incr=      c->dst_incr / c->src_incr;
      int compensation_distance= c->compensation_distance;
  
    if(compensation_distance == 0 && c->filter_length == 1 && c->phase_shift==0){
          int64_t index2= ((int64_t)index)<<32;
          int64_t incr= (1LL<<32) * c->dst_incr / c->src_incr;
          dst_size= FFMIN(dst_size, (src_size-1-index) * (int64_t)c->src_incr / c->dst_incr);
  
          for(dst_index=0; dst_index < dst_size; dst_index++){
              dst[dst_index] = src[index2>>32];
              index2 += incr;
          }
          index += dst_index * dst_incr;
          index += (frac + dst_index * (int64_t)dst_incr_frac) / c->src_incr;
          frac   = (frac + dst_index * (int64_t)dst_incr_frac) % c->src_incr;
    }else{
      for(dst_index=0; dst_index < dst_size; dst_index++){
          FELEM *filter= c->filter_bank + c->filter_length*(index & c->phase_mask);
          int sample_index= index >> c->phase_shift;
          FELEM2 val=0;
  
          if(sample_index < 0){
              for(i=0; i<c->filter_length; i++)
                  val += src[FFABS(sample_index + i) % src_size] * filter[i];
          }else if(sample_index + c->filter_length > src_size){
              break;
          }else if(c->linear){
              FELEM2 v2=0;
              for(i=0; i<c->filter_length; i++){
                  val += src[sample_index + i] * (FELEM2)filter[i];
                  v2  += src[sample_index + i] * (FELEM2)filter[i + c->filter_length];
              }
              val+=(v2-val)*(FELEML)frac / c->src_incr;
          }else{
              for(i=0; i<c->filter_length; i++){
                  val += src[sample_index + i] * (FELEM2)filter[i];
              }
          }
  
  #ifdef CONFIG_RESAMPLE_AUDIOPHILE_KIDDY_MODE
          dst[dst_index] = av_clip_int16(lrintf(val));
  #else
          val = (val + (1<<(FILTER_SHIFT-1)))>>FILTER_SHIFT;
          dst[dst_index] = (unsigned)(val + 32768) > 65535 ? (val>>31) ^ 32767 : val;
  #endif
  
          frac += dst_incr_frac;
          index += dst_incr;
          if(frac >= c->src_incr){
              frac -= c->src_incr;
              index++;
          }
  
          if(dst_index + 1 == compensation_distance){
              compensation_distance= 0;
              dst_incr_frac= c->ideal_dst_incr % c->src_incr;
              dst_incr=      c->ideal_dst_incr / c->src_incr;
          }
      }
    }
      *consumed= FFMAX(index, 0) >> c->phase_shift;
      if(index>=0) index &= c->phase_mask;
  
      if(compensation_distance){
          compensation_distance -= dst_index;
          av_assert2(compensation_distance > 0);
      }
      if(update_ctx){
          c->frac= frac;
          c->index= index;
          c->dst_incr= dst_incr_frac + c->src_incr*dst_incr;
          c->compensation_distance= compensation_distance;
      }
  
      return dst_index;
  }
  
  #endif
  