modules/audio_coding/codecs/ilbc/hp_output.c

/*
 *  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;
}