path: root/fdk-aac/libAACdec/src/rvlcconceal.cpp

/* -----------------------------------------------------------------------------
Software License for The Fraunhofer FDK AAC Codec Library for Android

© Copyright  1995 - 2018 Fraunhofer-Gesellschaft zur Förderung der angewandten
Forschung e.V. All rights reserved.

 1.    INTRODUCTION
The Fraunhofer FDK AAC Codec Library for Android ("FDK AAC Codec") is software
that implements the MPEG Advanced Audio Coding ("AAC") encoding and decoding
scheme for digital audio. This FDK AAC Codec software is intended to be used on
a wide variety of Android devices.

AAC's HE-AAC and HE-AAC v2 versions are regarded as today's most efficient
general perceptual audio codecs. AAC-ELD is considered the best-performing
full-bandwidth communications codec by independent studies and is widely
deployed. AAC has been standardized by ISO and IEC as part of the MPEG
specifications.

Patent licenses for necessary patent claims for the FDK AAC Codec (including
those of Fraunhofer) may be obtained through Via Licensing
(www.vialicensing.com) or through the respective patent owners individually for
the purpose of encoding or decoding bit streams in products that are compliant
with the ISO/IEC MPEG audio standards. Please note that most manufacturers of
Android devices already license these patent claims through Via Licensing or
directly from the patent owners, and therefore FDK AAC Codec software may
already be covered under those patent licenses when it is used for those
licensed purposes only.

Commercially-licensed AAC software libraries, including floating-point versions
with enhanced sound quality, are also available from Fraunhofer. Users are
encouraged to check the Fraunhofer website for additional applications
information and documentation.

2.    COPYRIGHT LICENSE

Redistribution and use in source and binary forms, with or without modification,
are permitted without payment of copyright license fees provided that you
satisfy the following conditions:

You must retain the complete text of this software license in redistributions of
the FDK AAC Codec or your modifications thereto in source code form.

You must retain the complete text of this software license in the documentation
and/or other materials provided with redistributions of the FDK AAC Codec or
your modifications thereto in binary form. You must make available free of
charge copies of the complete source code of the FDK AAC Codec and your
modifications thereto to recipients of copies in binary form.

The name of Fraunhofer may not be used to endorse or promote products derived
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of the FDK AAC Codec, the term "Fraunhofer FDK AAC Codec Library for Android"
must be replaced by the term "Third-Party Modified Version of the Fraunhofer FDK
AAC Codec Library for Android."

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NO EXPRESS OR IMPLIED LICENSES TO ANY PATENT CLAIMS, including without
limitation the patents of Fraunhofer, ARE GRANTED BY THIS SOFTWARE LICENSE.
Fraunhofer provides no warranty of patent non-infringement with respect to this
software.

You may use this FDK AAC Codec software or modifications thereto only for
purposes that are authorized by appropriate patent licenses.

4.    DISCLAIMER

This FDK AAC Codec software is provided by Fraunhofer on behalf of the copyright
holders and contributors "AS IS" and WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES,
including but not limited to the implied warranties of merchantability and
fitness for a particular purpose. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
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5.    CONTACT INFORMATION

Fraunhofer Institute for Integrated Circuits IIS
Attention: Audio and Multimedia Departments - FDK AAC LL
Am Wolfsmantel 33
91058 Erlangen, Germany

www.iis.fraunhofer.de/amm
amm-info@iis.fraunhofer.de
----------------------------------------------------------------------------- */

/**************************** AAC decoder library ******************************

   Author(s):

   Description:

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

/*!
  \file
  \brief  rvlc concealment
  \author Josef Hoepfl
*/

#include "rvlcconceal.h"

#include "block.h"
#include "rvlc.h"

/*---------------------------------------------------------------------------------------------
  function:      calcRefValFwd

  description:   The function determines the scalefactor which is closed to the
scalefactorband conceal_min. The same is done for intensity data and noise
energies.
-----------------------------------------------------------------------------------------------
  output:        - reference value scf
                 - reference value internsity data
                 - reference value noise energy
-----------------------------------------------------------------------------------------------
  return:        -
--------------------------------------------------------------------------------------------
*/

static void calcRefValFwd(CErRvlcInfo *pRvlc,
                          CAacDecoderChannelInfo *pAacDecoderChannelInfo,
                          int *refIsFwd, int *refNrgFwd, int *refScfFwd) {
  int band, bnds, group, startBand;
  int idIs, idNrg, idScf;
  int conceal_min, conceal_group_min;
  int MaximumScaleFactorBands;

  if (GetWindowSequence(&pAacDecoderChannelInfo->icsInfo) == BLOCK_SHORT)
    MaximumScaleFactorBands = 16;
  else
    MaximumScaleFactorBands = 64;

  conceal_min = pRvlc->conceal_min % MaximumScaleFactorBands;
  conceal_group_min = pRvlc->conceal_min / MaximumScaleFactorBands;

  /* calculate first reference value for approach in forward direction */
  idIs = idNrg = idScf = 1;

  /* set reference values */
  *refIsFwd = -SF_OFFSET;
  *refNrgFwd = pAacDecoderChannelInfo->pDynData->RawDataInfo.GlobalGain -
               SF_OFFSET - 90 - 256;
  *refScfFwd =
      pAacDecoderChannelInfo->pDynData->RawDataInfo.GlobalGain - SF_OFFSET;

  startBand = conceal_min - 1;
  for (group = conceal_group_min; group >= 0; group--) {
    for (band = startBand; band >= 0; band--) {
      bnds = 16 * group + band;
      switch (pAacDecoderChannelInfo->pDynData->aCodeBook[bnds]) {
        case ZERO_HCB:
          break;
        case INTENSITY_HCB:
        case INTENSITY_HCB2:
          if (idIs) {
            *refIsFwd =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
            idIs = 0; /* reference value has been set */
          }
          break;
        case NOISE_HCB:
          if (idNrg) {
            *refNrgFwd =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
            idNrg = 0; /* reference value has been set */
          }
          break;
        default:
          if (idScf) {
            *refScfFwd =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
            idScf = 0; /* reference value has been set */
          }
          break;
      }
    }
    startBand = pRvlc->maxSfbTransmitted - 1;
  }
}

/*---------------------------------------------------------------------------------------------
  function:      calcRefValBwd

  description:   The function determines the scalefactor which is closed to the
scalefactorband conceal_max. The same is done for intensity data and noise
energies.
-----------------------------------------------------------------------------------------------
  output:        - reference value scf
                 - reference value internsity data
                 - reference value noise energy
-----------------------------------------------------------------------------------------------
  return:        -
--------------------------------------------------------------------------------------------
*/

static void calcRefValBwd(CErRvlcInfo *pRvlc,
                          CAacDecoderChannelInfo *pAacDecoderChannelInfo,
                          int *refIsBwd, int *refNrgBwd, int *refScfBwd) {
  int band, bnds, group, startBand;
  int idIs, idNrg, idScf;
  int conceal_max, conceal_group_max;
  int MaximumScaleFactorBands;

  if (GetWindowSequence(&pAacDecoderChannelInfo->icsInfo) == BLOCK_SHORT)
    MaximumScaleFactorBands = 16;
  else
    MaximumScaleFactorBands = 64;

  conceal_max = pRvlc->conceal_max % MaximumScaleFactorBands;
  conceal_group_max = pRvlc->conceal_max / MaximumScaleFactorBands;

  /* calculate first reference value for approach in backward direction */
  idIs = idNrg = idScf = 1;

  /* set reference values */
  *refIsBwd = pRvlc->dpcm_is_last_position - SF_OFFSET;
  *refNrgBwd = pRvlc->rev_global_gain + pRvlc->dpcm_noise_last_position -
               SF_OFFSET - 90 - 256 + pRvlc->dpcm_noise_nrg;
  *refScfBwd = pRvlc->rev_global_gain - SF_OFFSET;

  startBand = conceal_max + 1;

  /* if needed, re-set reference values */
  for (group = conceal_group_max; group < pRvlc->numWindowGroups; group++) {
    for (band = startBand; band < pRvlc->maxSfbTransmitted; band++) {
      bnds = 16 * group + band;
      switch (pAacDecoderChannelInfo->pDynData->aCodeBook[bnds]) {
        case ZERO_HCB:
          break;
        case INTENSITY_HCB:
        case INTENSITY_HCB2:
          if (idIs) {
            *refIsBwd =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
            idIs = 0; /* reference value has been set */
          }
          break;
        case NOISE_HCB:
          if (idNrg) {
            *refNrgBwd =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
            idNrg = 0; /* reference value has been set */
          }
          break;
        default:
          if (idScf) {
            *refScfBwd =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
            idScf = 0; /* reference value has been set */
          }
          break;
      }
    }
    startBand = 0;
  }
}

/*---------------------------------------------------------------------------------------------
  function:      BidirectionalEstimation_UseLowerScfOfCurrentFrame

  description:   This approach by means of bidirectional estimation is generally
performed when a single bit error has been detected, the bit error can be
isolated between 'conceal_min' and 'conceal_max' and the 'sf_concealment' flag
is not set. The sets of scalefactors decoded in forward and backward direction
are compared with each other. The smaller scalefactor will be considered as the
correct one respectively. The reconstruction of the scalefactors with this
approach archieve good results in audio quality. The strategy must be applied to
scalefactors, intensity data and noise energy seperately.
-----------------------------------------------------------------------------------------------
  output:        Concealed scalefactor, noise energy and intensity data between
conceal_min and conceal_max
-----------------------------------------------------------------------------------------------
  return:        -
--------------------------------------------------------------------------------------------
*/

void BidirectionalEstimation_UseLowerScfOfCurrentFrame(
    CAacDecoderChannelInfo *pAacDecoderChannelInfo) {
  CErRvlcInfo *pRvlc =
      &pAacDecoderChannelInfo->pComData->overlay.aac.erRvlcInfo;
  int band, bnds, startBand, endBand, group;
  int conceal_min, conceal_max;
  int conceal_group_min, conceal_group_max;
  int MaximumScaleFactorBands;

  if (GetWindowSequence(&pAacDecoderChannelInfo->icsInfo) == BLOCK_SHORT) {
    MaximumScaleFactorBands = 16;
  } else {
    MaximumScaleFactorBands = 64;
  }

  /* If an error was detected just in forward or backward direction, set the
     corresponding border for concealment to a appropriate scalefactor band. The
     border is set to first or last sfb respectively, because the error will
     possibly not follow directly after the corrupt bit but just after decoding
     some more (wrong) scalefactors. */
  if (pRvlc->conceal_min == CONCEAL_MIN_INIT) pRvlc->conceal_min = 0;

  if (pRvlc->conceal_max == CONCEAL_MAX_INIT)
    pRvlc->conceal_max =
        (pRvlc->numWindowGroups - 1) * 16 + pRvlc->maxSfbTransmitted - 1;

  conceal_min = pRvlc->conceal_min % MaximumScaleFactorBands;
  conceal_group_min = pRvlc->conceal_min / MaximumScaleFactorBands;
  conceal_max = pRvlc->conceal_max % MaximumScaleFactorBands;
  conceal_group_max = pRvlc->conceal_max / MaximumScaleFactorBands;

  if (pRvlc->conceal_min == pRvlc->conceal_max) {
    int refIsFwd, refNrgFwd, refScfFwd;
    int refIsBwd, refNrgBwd, refScfBwd;

    bnds = pRvlc->conceal_min;
    calcRefValFwd(pRvlc, pAacDecoderChannelInfo, &refIsFwd, &refNrgFwd,
                  &refScfFwd);
    calcRefValBwd(pRvlc, pAacDecoderChannelInfo, &refIsBwd, &refNrgBwd,
                  &refScfBwd);

    switch (pAacDecoderChannelInfo->pDynData->aCodeBook[bnds]) {
      case ZERO_HCB:
        break;
      case INTENSITY_HCB:
      case INTENSITY_HCB2:
        if (refIsFwd < refIsBwd)
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = refIsFwd;
        else
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = refIsBwd;
        break;
      case NOISE_HCB:
        if (refNrgFwd < refNrgBwd)
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = refNrgFwd;
        else
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = refNrgBwd;
        break;
      default:
        if (refScfFwd < refScfBwd)
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = refScfFwd;
        else
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = refScfBwd;
        break;
    }
  } else {
    pAacDecoderChannelInfo->pComData->overlay.aac
        .aRvlcScfFwd[pRvlc->conceal_max] =
        pAacDecoderChannelInfo->pComData->overlay.aac
            .aRvlcScfBwd[pRvlc->conceal_max];
    pAacDecoderChannelInfo->pComData->overlay.aac
        .aRvlcScfBwd[pRvlc->conceal_min] =
        pAacDecoderChannelInfo->pComData->overlay.aac
            .aRvlcScfFwd[pRvlc->conceal_min];

    /* consider the smaller of the forward and backward decoded value as the
     * correct one */
    startBand = conceal_min;
    if (conceal_group_min == conceal_group_max)
      endBand = conceal_max;
    else
      endBand = pRvlc->maxSfbTransmitted - 1;

    for (group = conceal_group_min; group <= conceal_group_max; group++) {
      for (band = startBand; band <= endBand; band++) {
        bnds = 16 * group + band;
        if (pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds] <
            pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds])
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
              pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
        else
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
              pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
      }
      startBand = 0;
      if ((group + 1) == conceal_group_max) endBand = conceal_max;
    }
  }

  /* now copy all data to the output buffer which needs not to be concealed */
  if (conceal_group_min == 0)
    endBand = conceal_min;
  else
    endBand = pRvlc->maxSfbTransmitted;
  for (group = 0; group <= conceal_group_min; group++) {
    for (band = 0; band < endBand; band++) {
      bnds = 16 * group + band;
      pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
          pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
    }
    if ((group + 1) == conceal_group_min) endBand = conceal_min;
  }

  startBand = conceal_max + 1;
  for (group = conceal_group_max; group < pRvlc->numWindowGroups; group++) {
    for (band = startBand; band < pRvlc->maxSfbTransmitted; band++) {
      bnds = 16 * group + band;
      pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
          pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
    }
    startBand = 0;
  }
}

/*---------------------------------------------------------------------------------------------
  function:      BidirectionalEstimation_UseScfOfPrevFrameAsReference

  description:   This approach by means of bidirectional estimation is generally
performed when a single bit error has been detected, the bit error can be
isolated between 'conceal_min' and 'conceal_max', the 'sf_concealment' flag is
set and the previous frame has the same block type as the current frame. The
scalefactor decoded in forward and backward direction and the scalefactor of the
previous frame are compared with each other. The smaller scalefactor will be
considered as the correct one. At this the codebook of the previous and current
frame must be of the same set (scf, nrg, is) in each scalefactorband. Otherwise
the scalefactor of the previous frame is not considered in the minimum
calculation. The reconstruction of the scalefactors with this approach archieve
good results in audio quality. The strategy must be applied to scalefactors,
intensity data and noise energy seperately.
-----------------------------------------------------------------------------------------------
  output:        Concealed scalefactor, noise energy and intensity data between
conceal_min and conceal_max
-----------------------------------------------------------------------------------------------
  return:        -
--------------------------------------------------------------------------------------------
*/

void BidirectionalEstimation_UseScfOfPrevFrameAsReference(
    CAacDecoderChannelInfo *pAacDecoderChannelInfo,
    CAacDecoderStaticChannelInfo *pAacDecoderStaticChannelInfo) {
  CErRvlcInfo *pRvlc =
      &pAacDecoderChannelInfo->pComData->overlay.aac.erRvlcInfo;
  int band, bnds, startBand, endBand, group;
  int conceal_min, conceal_max;
  int conceal_group_min, conceal_group_max;
  int MaximumScaleFactorBands;
  SHORT commonMin;

  if (GetWindowSequence(&pAacDecoderChannelInfo->icsInfo) == BLOCK_SHORT) {
    MaximumScaleFactorBands = 16;
  } else {
    MaximumScaleFactorBands = 64;
  }

  /* If an error was detected just in forward or backward direction, set the
     corresponding border for concealment to a appropriate scalefactor band. The
     border is set to first or last sfb respectively, because the error will
     possibly not follow directly after the corrupt bit but just after decoding
     some more (wrong) scalefactors. */
  if (pRvlc->conceal_min == CONCEAL_MIN_INIT) pRvlc->conceal_min = 0;

  if (pRvlc->conceal_max == CONCEAL_MAX_INIT)
    pRvlc->conceal_max =
        (pRvlc->numWindowGroups - 1) * 16 + pRvlc->maxSfbTransmitted - 1;

  conceal_min = pRvlc->conceal_min % MaximumScaleFactorBands;
  conceal_group_min = pRvlc->conceal_min / MaximumScaleFactorBands;
  conceal_max = pRvlc->conceal_max % MaximumScaleFactorBands;
  conceal_group_max = pRvlc->conceal_max / MaximumScaleFactorBands;

  pAacDecoderChannelInfo->pComData->overlay.aac
      .aRvlcScfFwd[pRvlc->conceal_max] =
      pAacDecoderChannelInfo->pComData->overlay.aac
          .aRvlcScfBwd[pRvlc->conceal_max];
  pAacDecoderChannelInfo->pComData->overlay.aac
      .aRvlcScfBwd[pRvlc->conceal_min] =
      pAacDecoderChannelInfo->pComData->overlay.aac
          .aRvlcScfFwd[pRvlc->conceal_min];

  /* consider the smaller of the forward and backward decoded value as the
   * correct one */
  startBand = conceal_min;
  if (conceal_group_min == conceal_group_max)
    endBand = conceal_max;
  else
    endBand = pRvlc->maxSfbTransmitted - 1;

  for (group = conceal_group_min; group <= conceal_group_max; group++) {
    for (band = startBand; band <= endBand; band++) {
      bnds = 16 * group + band;
      switch (pAacDecoderChannelInfo->pDynData->aCodeBook[bnds]) {
        case ZERO_HCB:
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = 0;
          break;

        case INTENSITY_HCB:
        case INTENSITY_HCB2:
          if ((pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] == INTENSITY_HCB) ||
              (pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] == INTENSITY_HCB2)) {
            commonMin = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                fMin(commonMin, pAacDecoderStaticChannelInfo->concealmentInfo
                                    .aRvlcPreviousScaleFactor[bnds]);
          } else {
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
          }
          break;

        case NOISE_HCB:
          if (pAacDecoderStaticChannelInfo->concealmentInfo
                  .aRvlcPreviousCodebook[bnds] == NOISE_HCB) {
            commonMin = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                fMin(commonMin, pAacDecoderStaticChannelInfo->concealmentInfo
                                    .aRvlcPreviousScaleFactor[bnds]);
          } else {
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
          }
          break;

        default:
          if ((pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] != ZERO_HCB) &&
              (pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] != NOISE_HCB) &&
              (pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] != INTENSITY_HCB) &&
              (pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] != INTENSITY_HCB2)) {
            commonMin = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                fMin(commonMin, pAacDecoderStaticChannelInfo->concealmentInfo
                                    .aRvlcPreviousScaleFactor[bnds]);
          } else {
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
          }
          break;
      }
    }
    startBand = 0;
    if ((group + 1) == conceal_group_max) endBand = conceal_max;
  }

  /* now copy all data to the output buffer which needs not to be concealed */
  if (conceal_group_min == 0)
    endBand = conceal_min;
  else
    endBand = pRvlc->maxSfbTransmitted;
  for (group = 0; group <= conceal_group_min; group++) {
    for (band = 0; band < endBand; band++) {
      bnds = 16 * group + band;
      pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
          pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
    }
    if ((group + 1) == conceal_group_min) endBand = conceal_min;
  }

  startBand = conceal_max + 1;
  for (group = conceal_group_max; group < pRvlc->numWindowGroups; group++) {
    for (band = startBand; band < pRvlc->maxSfbTransmitted; band++) {
      bnds = 16 * group + band;
      pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
          pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
    }
    startBand = 0;
  }
}

/*---------------------------------------------------------------------------------------------
  function:      StatisticalEstimation

  description:   This approach by means of statistical estimation is generally
performed when both the start value and the end value are different and no
further errors have been detected. Considering the forward and backward decoded
scalefactors, the set with the lower scalefactors in sum will be considered as
the correct one. The scalefactors are differentially encoded. Normally it would
reach to compare one pair of the forward and backward decoded scalefactors to
specify the lower set. But having detected no further errors does not
necessarily mean the absence of errors. Therefore all scalefactors decoded in
forward and backward direction are summed up seperately. The set with the lower
sum will be used. The strategy must be applied to scalefactors, intensity data
and noise energy seperately.
-----------------------------------------------------------------------------------------------
  output:        Concealed scalefactor, noise energy and intensity data
-----------------------------------------------------------------------------------------------
  return:        -
--------------------------------------------------------------------------------------------
*/

void StatisticalEstimation(CAacDecoderChannelInfo *pAacDecoderChannelInfo) {
  CErRvlcInfo *pRvlc =
      &pAacDecoderChannelInfo->pComData->overlay.aac.erRvlcInfo;
  int band, bnds, group;
  int sumIsFwd, sumIsBwd;   /* sum of intensity data forward/backward */
  int sumNrgFwd, sumNrgBwd; /* sum of noise energy data forward/backward */
  int sumScfFwd, sumScfBwd; /* sum of scalefactor data forward/backward */
  int useIsFwd, useNrgFwd, useScfFwd; /* the flags signals the elements which
                                         are used for the final result */

  sumIsFwd = sumIsBwd = sumNrgFwd = sumNrgBwd = sumScfFwd = sumScfBwd = 0;
  useIsFwd = useNrgFwd = useScfFwd = 0;

  /* calculate sum of each group (scf,nrg,is) of forward and backward direction
   */
  for (group = 0; group < pRvlc->numWindowGroups; group++) {
    for (band = 0; band < pRvlc->maxSfbTransmitted; band++) {
      bnds = 16 * group + band;
      switch (pAacDecoderChannelInfo->pDynData->aCodeBook[bnds]) {
        case ZERO_HCB:
          break;

        case INTENSITY_HCB:
        case INTENSITY_HCB2:
          sumIsFwd +=
              pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
          sumIsBwd +=
              pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
          break;

        case NOISE_HCB:
          sumNrgFwd +=
              pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
          sumNrgBwd +=
              pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
          break;

        default:
          sumScfFwd +=
              pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
          sumScfBwd +=
              pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
          break;
      }
    }
  }

  /* find for each group (scf,nrg,is) the correct direction */
  if (sumIsFwd < sumIsBwd) useIsFwd = 1;

  if (sumNrgFwd < sumNrgBwd) useNrgFwd = 1;

  if (sumScfFwd < sumScfBwd) useScfFwd = 1;

  /* conceal each group (scf,nrg,is) */
  for (group = 0; group < pRvlc->numWindowGroups; group++) {
    for (band = 0; band < pRvlc->maxSfbTransmitted; band++) {
      bnds = 16 * group + band;
      switch (pAacDecoderChannelInfo->pDynData->aCodeBook[bnds]) {
        case ZERO_HCB:
          break;

        case INTENSITY_HCB:
        case INTENSITY_HCB2:
          if (useIsFwd)
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
          else
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
          break;

        case NOISE_HCB:
          if (useNrgFwd)
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
          else
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
          break;

        default:
          if (useScfFwd)
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds];
          else
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfBwd[bnds];
          break;
      }
    }
  }
}

/*---------------------------------------------------------------------------------------------
  description:   Approach by means of predictive interpolation
                 This approach by means of predictive estimation is generally
performed when the error cannot be isolated between 'conceal_min' and
'conceal_max', the 'sf_concealment' flag is set and the previous frame has the
same block type as the current frame. Check for each scalefactorband if the same
type of data (scalefactor, internsity data, noise energies) is transmitted. If
so use the scalefactor (intensity data, noise energy) in the current frame.
Otherwise set the scalefactor (intensity data, noise energy) for this
scalefactorband to zero.
-----------------------------------------------------------------------------------------------
  output:        Concealed scalefactor, noise energy and intensity data
-----------------------------------------------------------------------------------------------
  return:        -
--------------------------------------------------------------------------------------------
*/

void PredictiveInterpolation(
    CAacDecoderChannelInfo *pAacDecoderChannelInfo,
    CAacDecoderStaticChannelInfo *pAacDecoderStaticChannelInfo) {
  CErRvlcInfo *pRvlc =
      &pAacDecoderChannelInfo->pComData->overlay.aac.erRvlcInfo;
  int band, bnds, group;
  SHORT commonMin;

  for (group = 0; group < pRvlc->numWindowGroups; group++) {
    for (band = 0; band < pRvlc->maxSfbTransmitted; band++) {
      bnds = 16 * group + band;
      switch (pAacDecoderChannelInfo->pDynData->aCodeBook[bnds]) {
        case ZERO_HCB:
          pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = 0;
          break;

        case INTENSITY_HCB:
        case INTENSITY_HCB2:
          if ((pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] == INTENSITY_HCB) ||
              (pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] == INTENSITY_HCB2)) {
            commonMin = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                fMin(commonMin, pAacDecoderStaticChannelInfo->concealmentInfo
                                    .aRvlcPreviousScaleFactor[bnds]);
          } else {
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = -110;
          }
          break;

        case NOISE_HCB:
          if (pAacDecoderStaticChannelInfo->concealmentInfo
                  .aRvlcPreviousCodebook[bnds] == NOISE_HCB) {
            commonMin = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                fMin(commonMin, pAacDecoderStaticChannelInfo->concealmentInfo
                                    .aRvlcPreviousScaleFactor[bnds]);
          } else {
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = -110;
          }
          break;

        default:
          if ((pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] != ZERO_HCB) &&
              (pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] != NOISE_HCB) &&
              (pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] != INTENSITY_HCB) &&
              (pAacDecoderStaticChannelInfo->concealmentInfo
                   .aRvlcPreviousCodebook[bnds] != INTENSITY_HCB2)) {
            commonMin = fMin(
                pAacDecoderChannelInfo->pComData->overlay.aac.aRvlcScfFwd[bnds],
                pAacDecoderChannelInfo->pComData->overlay.aac
                    .aRvlcScfBwd[bnds]);
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] =
                fMin(commonMin, pAacDecoderStaticChannelInfo->concealmentInfo
                                    .aRvlcPreviousScaleFactor[bnds]);
          } else {
            pAacDecoderChannelInfo->pDynData->aScaleFactor[bnds] = 0;
          }
          break;
      }
    }
  }
}