src/modules/audio_coding/codecs/ilbc/hp_input.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_HpInput.c

******************************************************************/

#include "defines.h"

/*----------------------------------------------------------------*
 *  high-pass filter of input with *0.5 and saturation
 *---------------------------------------------------------------*/

void WebRtcIlbcfix_HpInput(
    WebRtc_Word16 *signal,     /* (i/o) signal vector */
    WebRtc_Word16 *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 */
    WebRtc_Word16 *y,      /* (i/o) Filter state yhi[n-1] ylow[n-1]
                                                                   yhi[n-2] ylow[n-2] */
    WebRtc_Word16 *x,      /* (i/o) Filter state x[n-1] x[n-2] */
    WebRtc_Word16 len)      /* (i)   Number of samples to filter */
{
  int i;
  WebRtc_Word32 tmpW32;
  WebRtc_Word32 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  = WEBRTC_SPL_MUL_16_16(y[1], ba[3]);     /* (-a[1])*y[i-1] (low part) */
    tmpW32 += WEBRTC_SPL_MUL_16_16(y[3], ba[4]);     /* (-a[2])*y[i-2] (low part) */
    tmpW32 = (tmpW32>>15);
    tmpW32 += WEBRTC_SPL_MUL_16_16(y[0], ba[3]);     /* (-a[1])*y[i-1] (high part) */
    tmpW32 += WEBRTC_SPL_MUL_16_16(y[2], ba[4]);     /* (-a[2])*y[i-2] (high part) */
    tmpW32 = (tmpW32<<1);

    tmpW32 += WEBRTC_SPL_MUL_16_16(signal[i], ba[0]);   /* b[0]*x[0] */
    tmpW32 += WEBRTC_SPL_MUL_16_16(x[0],      ba[1]);   /* b[1]*x[i-1] */
    tmpW32 += WEBRTC_SPL_MUL_16_16(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 2^12 */
    tmpW32b = tmpW32 + 4096;

    /* Saturate (to 2^28) so that the HP filtered signal does not overflow */
    tmpW32b = WEBRTC_SPL_SAT((WebRtc_Word32)268435455, tmpW32b, (WebRtc_Word32)-268435456);

    /* Convert back to Q0 and multiply with 0.5 */
    signal[i] = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmpW32b, 13);

    /* 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 = WEBRTC_SPL_LSHIFT_W32(tmpW32, 3);
    }

    y[0] = (WebRtc_Word16)(tmpW32 >> 16);
    y[1] = (WebRtc_Word16)((tmpW32 - WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)y[0], 16))>>1);
  }

  return;
}