text: /*
   *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
   *
   *  Use of this source code is governed by a BSD-style license
   *  that can be found in the LICENSE file in the root of the source
   *  tree. An additional intellectual property rights grant can be found
   *  in the file PATENTS.  All contributing project authors may
   *  be found in the AUTHORS file in the root of the source tree.
   */
  
  /******************************************************************
  
   iLBC Speech Coder ANSI-C Source Code
  
   WebRtcIlbcfix_HpOutput.c
  
  ******************************************************************/
  
  #include "modules/audio_coding/codecs/ilbc/defines.h"
  
  /*----------------------------------------------------------------*
   *  high-pass filter of output and *2 with saturation
   *---------------------------------------------------------------*/
  
  void WebRtcIlbcfix_HpOutput(
      int16_t *signal,     /* (i/o) signal vector */
      int16_t *ba,      /* (i)   B- and A-coefficients (2:nd order)
                                                                     {b[0] b[1] b[2] -a[1] -a[2]} a[0]
                                                                     is assumed to be 1.0 */
      int16_t *y,      /* (i/o) Filter state yhi[n-1] ylow[n-1]
                                                                     yhi[n-2] ylow[n-2] */
      int16_t *x,      /* (i/o) Filter state x[n-1] x[n-2] */
      size_t len)      /* (i)   Number of samples to filter */
  {
    size_t i;
    int32_t tmpW32;
    int32_t tmpW32b;
  
    for (i=0; i<len; i++) {
  
      /*
        y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2]
        + (-a[1])*y[i-1] + (-a[2])*y[i-2];
      */
  
      tmpW32 = y[1] * ba[3];  /* (-a[1])*y[i-1] (low part) */
      tmpW32 += y[3] * ba[4];  /* (-a[2])*y[i-2] (low part) */
      tmpW32 = (tmpW32>>15);
      tmpW32 += y[0] * ba[3];  /* (-a[1])*y[i-1] (high part) */
      tmpW32 += y[2] * ba[4];  /* (-a[2])*y[i-2] (high part) */
      tmpW32 *= 2;
  
      tmpW32 += signal[i] * ba[0];  /* b[0]*x[0] */
      tmpW32 += x[0] * ba[1];  /* b[1]*x[i-1] */
      tmpW32 += x[1] * ba[2];  /* b[2]*x[i-2] */
  
      /* Update state (input part) */
      x[1] = x[0];
      x[0] = signal[i];
  
      /* Rounding in Q(12-1), i.e. add 2^10 */
      tmpW32b = tmpW32 + 1024;
  
      /* Saturate (to 2^26) so that the HP filtered signal does not overflow */
      tmpW32b = WEBRTC_SPL_SAT((int32_t)67108863, tmpW32b, (int32_t)-67108864);
  
      /* Convert back to Q0 and multiply with 2 */
      signal[i] = (int16_t)(tmpW32b >> 11);
  
      /* Update state (filtered part) */
      y[2] = y[0];
      y[3] = y[1];
  
      /* upshift tmpW32 by 3 with saturation */
      if (tmpW32>268435455) {
        tmpW32 = WEBRTC_SPL_WORD32_MAX;
      } else if (tmpW32<-268435456) {
        tmpW32 = WEBRTC_SPL_WORD32_MIN;
      } else {
        tmpW32 *= 8;
      }
  
      y[0] = (int16_t)(tmpW32 >> 16);
      y[1] = (int16_t)((tmpW32 & 0xffff) >> 1);
  
    }
  
    return;
  }
  