xref: /external/aac/libAACenc/src/aacenc_tns.cpp

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

� Copyright  1995 - 2012 Fraunhofer-Gesellschaft zur F�rderung 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
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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
----------------------------------------------------------------------------------------------------------- */

/******************************** MPEG Audio Encoder **************************

   Initial author:       Alex Groeschel
   contents/description: Temporal noise shaping

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

#include "aacenc_tns.h"
#include "psy_const.h"
#include "psy_configuration.h"
#include "tns_func.h"
#include "aacEnc_rom.h"
#include "aacenc_tns.h"

enum {
    HIFILT = 0, /* index of higher filter */
    LOFILT = 1 /* index of lower filter */
};


#define FILTER_DIRECTION 0

static const FIXP_DBL acfWindowLong[12+3+1] = {
  0x7fffffff,0x7fb80000,0x7ee00000,0x7d780000,0x7b800000,0x78f80000,0x75e00000,0x72380000,
  0x6e000000,0x69380000,0x63e00000,0x5df80000,0x57800000,0x50780000,0x48e00000,0x40b80000
};

static const FIXP_DBL acfWindowShort[4+3+1] = {
  0x7fffffff,0x7e000000,0x78000000,0x6e000000,0x60000000,0x4e000000,0x38000000,0x1e000000
};


typedef struct {
  INT      filterEnabled[MAX_NUM_OF_FILTERS];
  INT      threshOn[MAX_NUM_OF_FILTERS];                /* min. prediction gain for using tns TABUL*/
  INT      filterStartFreq[MAX_NUM_OF_FILTERS];         /* lowest freq for lpc TABUL*/
  INT      tnsLimitOrder[MAX_NUM_OF_FILTERS];           /* Limit for TNS order TABUL*/
  INT      tnsFilterDirection[MAX_NUM_OF_FILTERS];      /* Filtering direction, 0=up, 1=down TABUL */
  INT      acfSplit[MAX_NUM_OF_FILTERS];
  FIXP_DBL tnsTimeResolution[MAX_NUM_OF_FILTERS];       /* TNS max. time resolution TABUL. Should be fract but MSVC won't compile then */
  INT      seperateFiltersAllowed;

} TNS_PARAMETER_TABULATED;


typedef struct{
  INT                      bitRateFrom[2];  /* noneSbr=0, useSbr=1 */
  INT                      bitRateTo[2];    /* noneSbr=0, useSbr=1 */
  TNS_PARAMETER_TABULATED  paramTab[2];     /* mono=0, stereo=1 */

} TNS_INFO_TAB;

#define TNS_TIMERES_SCALE    (1)
#define FL2_TIMERES_FIX(a)   ( FL2FXCONST_DBL(a/(float)(1<<TNS_TIMERES_SCALE)) )

static const TNS_INFO_TAB tnsInfoTab[] =
{
  {
    {  16000,  13500},
    {  32000,  28000},
    {
      { {1, 1}, {1437, 1500}, {1400, 600}, {12, 12}, {FILTER_DIRECTION, FILTER_DIRECTION}, {3, 1}, {FL2_TIMERES_FIX(0.4f), FL2_TIMERES_FIX(1.2f)}, 1 },
      { {1, 1}, {1437, 1500}, {1400, 600}, {12, 12}, {FILTER_DIRECTION, FILTER_DIRECTION}, {3, 1}, {FL2_TIMERES_FIX(0.4f), FL2_TIMERES_FIX(1.2f)}, 1 }
    }
  },
  {
    {  32001,  28001},
    {  60000,  52000},
    {
      { {1, 1}, {1437, 1500}, {1400, 600}, {12, 10}, {FILTER_DIRECTION, FILTER_DIRECTION}, {3, 1}, {FL2_TIMERES_FIX(0.4f), FL2_TIMERES_FIX(1.0f)}, 1 },
      { {1, 1}, {1437, 1500}, {1400, 600}, {12, 10}, {FILTER_DIRECTION, FILTER_DIRECTION}, {3, 1}, {FL2_TIMERES_FIX(0.4f), FL2_TIMERES_FIX(1.0f)}, 1 }
    }
  },
  {
    {  60001,  52001},
    { 384000, 384000},
    {
      { {1, 1}, {1437, 1500}, {1400, 600}, {12,  8}, {FILTER_DIRECTION, FILTER_DIRECTION}, {3, 1}, {FL2_TIMERES_FIX(0.4f), FL2_TIMERES_FIX(1.0f)}, 1 },
      { {1, 1}, {1437, 1500}, {1400, 600}, {12,  8}, {FILTER_DIRECTION, FILTER_DIRECTION}, {3, 1}, {FL2_TIMERES_FIX(0.4f), FL2_TIMERES_FIX(1.0f)}, 1 }
    }
  }
};

typedef struct {
  INT   samplingRate;
  SCHAR maxBands[2]; /* long=0; short=1 */

} TNS_MAX_TAB_ENTRY;

static const TNS_MAX_TAB_ENTRY tnsMaxBandsTab1024[] =
{
  { 96000, { 31,  9}},
  { 88200, { 31,  9}},
  { 64000, { 34, 10}},
  { 48000, { 40, 14}},
  { 44100, { 42, 14}},
  { 32000, { 51, 14}},
  { 24000, { 46, 14}},
  { 22050, { 46, 14}},
  { 16000, { 42, 14}},
  { 12000, { 42, 14}},
  { 11025, { 42, 14}},
  { 8000,  { 39, 14}}
};

static const TNS_MAX_TAB_ENTRY tnsMaxBandsTab480[] =
{
  { 48000, { 31, -1}},
  { 44100, { 32, -1}},
  { 32000, { 37, -1}},
  { 24000, { 30, -1}},
  { 22050, { 30, -1}}
};

static const TNS_MAX_TAB_ENTRY tnsMaxBandsTab512[] =
{
  { 48000, { 31, -1}},
  { 44100, { 32, -1}},
  { 32000, { 37, -1}},
  { 24000, { 31, -1}},
  { 22050, { 31, -1}}
};

static INT FDKaacEnc_AutoToParcor(
        FIXP_DBL *RESTRICT input,
        FIXP_DBL *RESTRICT reflCoeff,
        const INT numOfCoeff
        );

static void FDKaacEnc_Parcor2Index(
        const FIXP_DBL *parcor,
        INT *RESTRICT index,
        const INT order,
        const INT bitsPerCoeff
        );

static void FDKaacEnc_Index2Parcor(
        const INT *index,
        FIXP_DBL *RESTRICT parcor,
        const INT order,
        const INT bitsPerCoeff
        );

static INT FDKaacEnc_ParcorToLpc(
        const FIXP_DBL *reflCoeff,
        FIXP_DBL *RESTRICT LpcCoeff,
        const INT numOfCoeff,
        FIXP_DBL *RESTRICT workBuffer
        );

static void FDKaacEnc_AnalysisFilter(
        FIXP_DBL *RESTRICT signal,
        const INT numOfLines,
        const FIXP_DBL *predictorCoeff,
        const INT order,
        const INT lpcGainFactor
        );

static void FDKaacEnc_CalcGaussWindow(
        FIXP_DBL *win,
        const int winSize,
        const INT samplingRate,
        const INT transformResolution,
        const FIXP_DBL timeResolution,
        const INT timeResolution_e
        );

static const TNS_PARAMETER_TABULATED* FDKaacEnc_GetTnsParam(
        const INT bitRate,
        const INT channels,
        const INT sbrLd
        )
{
  int i;
  const TNS_PARAMETER_TABULATED *tnsConfigTab = NULL;

  for (i = 0; i < (int) (sizeof(tnsInfoTab)/sizeof(TNS_INFO_TAB)); i++) {
    if ((bitRate >= tnsInfoTab[i].bitRateFrom[sbrLd?1:0]) &&
         bitRate <= tnsInfoTab[i].bitRateTo[sbrLd?1:0])
    {
      tnsConfigTab = &tnsInfoTab[i].paramTab[(channels==1)?0:1];
    }
  }

  return tnsConfigTab;
}


static INT getTnsMaxBands(
        const INT sampleRate,
        const INT granuleLength,
        const INT isShortBlock
        )
{
  int i;
  INT numBands = -1;
  const TNS_MAX_TAB_ENTRY *pMaxBandsTab = NULL;
  int maxBandsTabSize = 0;

  switch (granuleLength) {
    case 960:
    case 1024:
      pMaxBandsTab = tnsMaxBandsTab1024;
      maxBandsTabSize = sizeof(tnsMaxBandsTab1024)/sizeof(TNS_MAX_TAB_ENTRY);
      break;
    case 480:
      pMaxBandsTab = tnsMaxBandsTab480;
      maxBandsTabSize = sizeof(tnsMaxBandsTab480)/sizeof(TNS_MAX_TAB_ENTRY);
      break;
    case 512:
      pMaxBandsTab = tnsMaxBandsTab512;
      maxBandsTabSize = sizeof(tnsMaxBandsTab512)/sizeof(TNS_MAX_TAB_ENTRY);
      break;
    default:
      numBands = -1;
  }

  if (pMaxBandsTab!=NULL) {
    for (i=0; i<maxBandsTabSize; i++) {
      numBands = pMaxBandsTab[i].maxBands[(!isShortBlock)?0:1];
      if (sampleRate >= pMaxBandsTab[i].samplingRate) {
        break;
      }
    }
  }

  return numBands;
}

/***************************************************************************/
/*!
  \brief     FDKaacEnc_FreqToBandWithRounding

  Returns index of nearest band border

  \param frequency
  \param sampling frequency
  \param total number of bands
  \param pointer to table of band borders

  \return band border
****************************************************************************/

INT FDKaacEnc_FreqToBandWithRounding(
        const INT freq,
        const INT fs,
        const INT numOfBands,
        const INT *bandStartOffset
        )
{
  INT lineNumber, band;

  /*  assert(freq >= 0);  */
  lineNumber = (freq*bandStartOffset[numOfBands]*4/fs+1)/2;

  /* freq > fs/2 */
  if (lineNumber >= bandStartOffset[numOfBands])
    return numOfBands;

  /* find band the line number lies in */
  for (band=0; band<numOfBands; band++) {
    if (bandStartOffset[band+1]>lineNumber) break;
  }

  /* round to nearest band border */
  if (lineNumber - bandStartOffset[band] >
      bandStartOffset[band+1] - lineNumber )
    {
      band++;
    }

  return(band);
}


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

    functionname: FDKaacEnc_InitTnsConfiguration
    description:  fill TNS_CONFIG structure with sensible content
    returns:
    input:        bitrate, samplerate, number of channels,
                  blocktype (long or short),
                  TNS Config struct (modified),
                  psy config struct,
                  tns active flag
    output:

*****************************************************************************/
AAC_ENCODER_ERROR FDKaacEnc_InitTnsConfiguration(INT bitRate,
                                                 INT sampleRate,
                                                 INT channels,
                                                 INT blockType,
                                                 INT granuleLength,
                                                 INT ldSbrPresent,
                                                 TNS_CONFIG *tC,
                                                 PSY_CONFIGURATION *pC,
                                                 INT active,
                                                 INT useTnsPeak)
{
  int i;
  //float acfTimeRes   = (blockType == SHORT_WINDOW) ? 0.125f : 0.046875f;

  if (channels <= 0)
    return (AAC_ENCODER_ERROR)1;

  /* initialize TNS filter flag, order, and coefficient resolution (in bits per coeff) */
  tC->tnsActive      = (active) ? TRUE : FALSE;
  tC->maxOrder       = (blockType == SHORT_WINDOW) ? 5 : 12;  /* maximum: 7, 20 */
  if (bitRate < 16000)
    tC->maxOrder -= 2;
  tC->coefRes        = (blockType == SHORT_WINDOW) ? 3 : 4;

  /* LPC stop line: highest MDCT line to be coded, but do not go beyond TNS_MAX_BANDS! */
  tC->lpcStopBand = getTnsMaxBands(sampleRate, granuleLength, (blockType == SHORT_WINDOW) ? 1 : 0);

  if (tC->lpcStopBand < 0) {
    return (AAC_ENCODER_ERROR)1;
  }

  tC->lpcStopBand = FDKmin(tC->lpcStopBand, pC->sfbActive);
  tC->lpcStopLine    = pC->sfbOffset[tC->lpcStopBand];

  switch (granuleLength) {
    case 960:
    case 1024:
      /* TNS start line: skip lower MDCT lines to prevent artifacts due to filter mismatch */
      tC->lpcStartBand[LOFILT]   = (blockType == SHORT_WINDOW) ? 0 : ((sampleRate < 18783) ? 4 : 8);
      tC->lpcStartLine[LOFILT]   = pC->sfbOffset[tC->lpcStartBand[LOFILT]];

      i = tC->lpcStopBand;
      while (pC->sfbOffset[i] > (tC->lpcStartLine[LOFILT] + (tC->lpcStopLine - tC->lpcStartLine[LOFILT]) / 4)) i--;
      tC->lpcStartBand[HIFILT]   = i;
      tC->lpcStartLine[HIFILT]   = pC->sfbOffset[i];

      tC->confTab.threshOn[HIFILT] = 1437;
      tC->confTab.threshOn[LOFILT] = 1500;

      tC->confTab.tnsLimitOrder[HIFILT] = tC->maxOrder;
      tC->confTab.tnsLimitOrder[LOFILT] = tC->maxOrder - 7;

      tC->confTab.tnsFilterDirection[HIFILT] = FILTER_DIRECTION;
      tC->confTab.tnsFilterDirection[LOFILT] = FILTER_DIRECTION;

      tC->confTab.acfSplit[HIFILT] = -1;  /* signal Merged4to2QuartersAutoCorrelation in FDKaacEnc_MergedAutoCorrelation*/
      tC->confTab.acfSplit[LOFILT] = -1;  /* signal Merged4to2QuartersAutoCorrelation in FDKaacEnc_MergedAutoCorrelation */

      tC->confTab.filterEnabled[HIFILT] = 1;
      tC->confTab.filterEnabled[LOFILT] = 1;
      tC->confTab.seperateFiltersAllowed = 1;

      /* compute autocorrelation window based on maximum filter order for given block type */
      /* for (i = 0; i <= tC->maxOrder + 3; i++) {
           float acfWinTemp = acfTimeRes * i;
           acfWindow[i] = FL2FXCONST_DBL(1.0f - acfWinTemp * acfWinTemp);
         }
      */
      if (blockType == SHORT_WINDOW) {
        FDKmemcpy(tC->acfWindow[HIFILT], acfWindowShort, FDKmin(sizeof(acfWindowShort), sizeof(tC->acfWindow[HIFILT])));
        FDKmemcpy(tC->acfWindow[LOFILT], acfWindowShort, FDKmin(sizeof(acfWindowShort), sizeof(tC->acfWindow[HIFILT])));
      }
      else {
        FDKmemcpy(tC->acfWindow[HIFILT], acfWindowLong, FDKmin(sizeof(acfWindowLong), sizeof(tC->acfWindow[HIFILT])));
        FDKmemcpy(tC->acfWindow[LOFILT], acfWindowLong, FDKmin(sizeof(acfWindowLong), sizeof(tC->acfWindow[HIFILT])));
      }
      break;
    case 480:
    case 512:
      {
        const TNS_PARAMETER_TABULATED* pCfg = FDKaacEnc_GetTnsParam(bitRate, channels, ldSbrPresent);

        if ( pCfg != NULL ) {
          tC->lpcStartBand[HIFILT]         = FDKaacEnc_FreqToBandWithRounding(pCfg->filterStartFreq[HIFILT], sampleRate, pC->sfbCnt, pC->sfbOffset);
          tC->lpcStartLine[HIFILT]         = pC->sfbOffset[tC->lpcStartBand[HIFILT]];
          tC->lpcStartBand[LOFILT]         = FDKaacEnc_FreqToBandWithRounding(pCfg->filterStartFreq[LOFILT], sampleRate, pC->sfbCnt, pC->sfbOffset);
          tC->lpcStartLine[LOFILT]         = pC->sfbOffset[tC->lpcStartBand[LOFILT]];

          tC->confTab.threshOn[HIFILT] = pCfg->threshOn[HIFILT];
          tC->confTab.threshOn[LOFILT] = pCfg->threshOn[LOFILT];

          tC->confTab.tnsLimitOrder[HIFILT] = pCfg->tnsLimitOrder[HIFILT];
          tC->confTab.tnsLimitOrder[LOFILT] = pCfg->tnsLimitOrder[LOFILT];

          tC->confTab.tnsFilterDirection[HIFILT] = pCfg->tnsFilterDirection[HIFILT];
          tC->confTab.tnsFilterDirection[LOFILT] = pCfg->tnsFilterDirection[LOFILT];

          tC->confTab.acfSplit[HIFILT] = pCfg->acfSplit[HIFILT];
          tC->confTab.acfSplit[LOFILT] = pCfg->acfSplit[LOFILT];

          tC->confTab.filterEnabled[HIFILT] = pCfg->filterEnabled[HIFILT];
          tC->confTab.filterEnabled[LOFILT] = pCfg->filterEnabled[LOFILT];
          tC->confTab.seperateFiltersAllowed = pCfg->seperateFiltersAllowed;

          FDKaacEnc_CalcGaussWindow(tC->acfWindow[HIFILT], tC->maxOrder+1, sampleRate, granuleLength, pCfg->tnsTimeResolution[HIFILT], TNS_TIMERES_SCALE);
          FDKaacEnc_CalcGaussWindow(tC->acfWindow[LOFILT], tC->maxOrder+1, sampleRate, granuleLength, pCfg->tnsTimeResolution[LOFILT], TNS_TIMERES_SCALE);
        }
        else {
          tC->tnsActive = FALSE; /* no configuration available, disable tns tool */
        }
      }
      break;
    default:
      tC->tnsActive = FALSE; /* no configuration available, disable tns tool */
  }

  return AAC_ENC_OK;

}

/***************************************************************************/
/*!
  \brief     FDKaacEnc_ScaleUpSpectrum

  Scales up spectrum lines in a given frequency section

  \param scaled spectrum
  \param original spectrum
  \param frequency line to start scaling
  \param frequency line to enc scaling

  \return scale factor

****************************************************************************/
static inline INT FDKaacEnc_ScaleUpSpectrum(
        FIXP_DBL                 *dest,
        const FIXP_DBL           *src,
        const INT                 startLine,
        const INT                 stopLine
        )
{
    INT i, scale;

    FIXP_DBL maxVal = FL2FXCONST_DBL(0.f);

    /* Get highest value in given spectrum */
    for (i=startLine; i<stopLine; i++) {
      maxVal = fixMax(maxVal,fixp_abs(src[i]));
    }
    scale = CountLeadingBits(maxVal);

    /* Scale spectrum according to highest value */
    for (i=startLine; i<stopLine; i++) {
      dest[i] = src[i]<<scale;
    }

    return scale;
}

/***************************************************************************/
/*!
  \brief     FDKaacEnc_CalcAutoCorrValue

  Calculate autocorellation value for one lag

  \param pointer to spectrum
  \param start line
  \param stop line
  \param lag to be calculated
  \param scaling of the lag

****************************************************************************/
static inline FIXP_DBL FDKaacEnc_CalcAutoCorrValue(
        const FIXP_DBL           *spectrum,
        const INT                 startLine,
        const INT                 stopLine,
        const INT                 lag,
        const INT                 scale
        )
{
    int i;
    FIXP_DBL result = FL2FXCONST_DBL(0.f);

    if (lag==0) {
      for (i=startLine; i<stopLine; i++) {
        result += (fPow2(spectrum[i])>>scale);
      }
    }
    else {
      for (i=startLine; i<(stopLine-lag); i++) {
        result += (fMult(spectrum[i], spectrum[i+lag])>>scale);
      }
    }

    return result;
}

/***************************************************************************/
/*!
  \brief     FDKaacEnc_AutoCorrNormFac

  Autocorrelation function for 1st and 2nd half of the spectrum

  \param pointer to spectrum
  \param pointer to autocorrelation window
  \param filter start line

****************************************************************************/
static inline FIXP_DBL FDKaacEnc_AutoCorrNormFac(
        const FIXP_DBL            value,
        const INT                 scale,
        INT                      *sc
        )
{
    #define HLM_MIN_NRG 0.0000000037252902984619140625f /* 2^-28 */
    #define MAX_INV_NRGFAC (1.f/HLM_MIN_NRG)

    FIXP_DBL retValue;
    FIXP_DBL A, B;

    if (scale>=0) {
      A = value;
      B = FL2FXCONST_DBL(HLM_MIN_NRG)>>fixMin(DFRACT_BITS-1,scale);
    }
    else {
      A = value>>fixMin(DFRACT_BITS-1,(-scale));
      B = FL2FXCONST_DBL(HLM_MIN_NRG);
    }

    if (A > B) {
      int shift = 0;
      FIXP_DBL tmp = invSqrtNorm2(value,&shift);

      retValue = fMult(tmp,tmp);
      *sc += (2*shift);
    }
    else {
      /* MAX_INV_NRGFAC*FDKpow(2,-28) = 1/2^-28 * 2^-28 = 1.0 */
      retValue = /*FL2FXCONST_DBL(MAX_INV_NRGFAC*FDKpow(2,-28))*/ (FIXP_DBL)MAXVAL_DBL;
      *sc += scale+28;
    }

    return retValue;
}

static void FDKaacEnc_MergedAutoCorrelation(
        const FIXP_DBL           *spectrum,
        const FIXP_DBL            acfWindow[MAX_NUM_OF_FILTERS][TNS_MAX_ORDER+3+1],
        const INT                 lpcStartLine[MAX_NUM_OF_FILTERS],
        const INT                 lpcStopLine,
        const INT                 maxOrder,
        const INT                 acfSplit[MAX_NUM_OF_FILTERS],
        FIXP_DBL                 *_rxx1,
        FIXP_DBL                 *_rxx2
        )
{
    int i, idx0, idx1, idx2, idx3, idx4, lag;
    FIXP_DBL rxx1_0, rxx2_0, rxx3_0, rxx4_0;

    /* buffer for temporal spectrum */
    C_ALLOC_SCRATCH_START(pSpectrum, FIXP_DBL, (1024));

    /* pre-initialization output */
    FDKmemclear(&_rxx1[0], sizeof(FIXP_DBL)*(maxOrder+1));
    FDKmemclear(&_rxx2[0], sizeof(FIXP_DBL)*(maxOrder+1));

    /* MDCT line indices separating the 1st, 2nd, 3rd, and 4th analysis quarters */
    if ( (acfSplit[LOFILT]==-1) || (acfSplit[HIFILT]==-1) ) {
      /* autocorrelation function for 1st, 2nd, 3rd, and 4th quarter of the spectrum */
      idx0 = lpcStartLine[LOFILT];
      i    = lpcStopLine - lpcStartLine[LOFILT];
      idx1 = idx0 + i / 4;
      idx2 = idx0 + i / 2;
      idx3 = idx0 + i * 3 / 4;
      idx4 = lpcStopLine;
    }
    else {
      FDK_ASSERT(acfSplit[LOFILT]==1);
      FDK_ASSERT(acfSplit[HIFILT]==3);
      i    = (lpcStopLine - lpcStartLine[HIFILT]) / 3;
      idx0 = lpcStartLine[LOFILT];
      idx1 = lpcStartLine[HIFILT];
      idx2 = idx1 + i;
      idx3 = idx2 + i;
      idx4 = lpcStopLine;
    }

    /* copy spectrum to temporal buffer and scale up as much as possible */
    INT sc1 = FDKaacEnc_ScaleUpSpectrum(pSpectrum, spectrum, idx0, idx1);
    INT sc2 = FDKaacEnc_ScaleUpSpectrum(pSpectrum, spectrum, idx1, idx2);
    INT sc3 = FDKaacEnc_ScaleUpSpectrum(pSpectrum, spectrum, idx2, idx3);
    INT sc4 = FDKaacEnc_ScaleUpSpectrum(pSpectrum, spectrum, idx3, idx4);

    /* get scaling values for summation */
    INT nsc1, nsc2, nsc3, nsc4;
    for (nsc1=1; (1<<nsc1)<(idx1-idx0); nsc1++);
    for (nsc2=1; (1<<nsc2)<(idx2-idx1); nsc2++);
    for (nsc3=1; (1<<nsc3)<(idx3-idx2); nsc3++);
    for (nsc4=1; (1<<nsc4)<(idx4-idx3); nsc4++);

    /* compute autocorrelation value at lag zero, i. e. energy, for each quarter */
    rxx1_0 = FDKaacEnc_CalcAutoCorrValue(pSpectrum, idx0, idx1, 0, nsc1);
    rxx2_0 = FDKaacEnc_CalcAutoCorrValue(pSpectrum, idx1, idx2, 0, nsc2);
    rxx3_0 = FDKaacEnc_CalcAutoCorrValue(pSpectrum, idx2, idx3, 0, nsc3);
    rxx4_0 = FDKaacEnc_CalcAutoCorrValue(pSpectrum, idx3, idx4, 0, nsc4);

    /* compute energy normalization factors, i. e. 1/energy (saves some divisions) */
    if (rxx1_0 != FL2FXCONST_DBL(0.f))
    {
        INT sc_fac1 = -1;
        FIXP_DBL fac1 = FDKaacEnc_AutoCorrNormFac(rxx1_0, ((-2*sc1)+nsc1), &sc_fac1);
        _rxx1[0] = scaleValue(fMult(rxx1_0,fac1),sc_fac1);

        for (lag = 1; lag <= maxOrder; lag++) {
          /* compute energy-normalized and windowed autocorrelation values at this lag */
          if ((3 * lag) <= maxOrder + 3) {
              FIXP_DBL x1 = FDKaacEnc_CalcAutoCorrValue(pSpectrum, idx0, idx1, lag, nsc1);
              _rxx1[lag] = fMult(scaleValue(fMult(x1,fac1),sc_fac1), acfWindow[LOFILT][3*lag]);
          }
        }
    }

    /* auto corr over upper 3/4 of spectrum */
    if ( !((rxx2_0 == FL2FXCONST_DBL(0.f)) && (rxx3_0 == FL2FXCONST_DBL(0.f)) && (rxx4_0 == FL2FXCONST_DBL(0.f))) )
    {
        FIXP_DBL fac2, fac3, fac4;
        fac2 = fac3 = fac4 = FL2FXCONST_DBL(0.f);
        INT sc_fac2, sc_fac3, sc_fac4;
        sc_fac2 = sc_fac3 = sc_fac4 = 0;

        if (rxx2_0!=FL2FXCONST_DBL(0.f)) {
          fac2 = FDKaacEnc_AutoCorrNormFac(rxx2_0, ((-2*sc2)+nsc2), &sc_fac2);
          sc_fac2 -= 2;
        }
        if (rxx3_0!=FL2FXCONST_DBL(0.f)) {
          fac3 = FDKaacEnc_AutoCorrNormFac(rxx3_0, ((-2*sc3)+nsc3), &sc_fac3);
          sc_fac3 -= 2;
        }
        if (rxx4_0!=FL2FXCONST_DBL(0.f)) {
          fac4 = FDKaacEnc_AutoCorrNormFac(rxx4_0, ((-2*sc4)+nsc4), &sc_fac4);
          sc_fac4 -= 2;
        }

        _rxx2[0] = scaleValue(fMult(rxx2_0,fac2),sc_fac2) +
                   scaleValue(fMult(rxx3_0,fac3),sc_fac3) +
                   scaleValue(fMult(rxx4_0,fac4),sc_fac4);

        for (lag = 1; lag <= maxOrder; lag++) {
          /* merge quarters 2, 3, 4 into one autocorrelation; quarter 1 stays separate */
          FIXP_DBL x2 = scaleValue(fMult(FDKaacEnc_CalcAutoCorrValue(pSpectrum, idx1, idx2, lag, nsc2), fac2),sc_fac2) +
                        scaleValue(fMult(FDKaacEnc_CalcAutoCorrValue(pSpectrum, idx2, idx3, lag, nsc3), fac3),sc_fac3) +
                        scaleValue(fMult(FDKaacEnc_CalcAutoCorrValue(pSpectrum, idx3, idx4, lag, nsc4), fac4),sc_fac4);

          _rxx2[lag] = fMult(x2, acfWindow[HIFILT][lag]);
        }
    }

    C_ALLOC_SCRATCH_END(pSpectrum, FIXP_DBL, (1024));
}


/*****************************************************************************
    functionname: FDKaacEnc_TnsDetect
    description:  do decision, if TNS shall be used or not
    returns:
    input:        tns data structure (modified),
                  tns config structure,
                  scalefactor size and table,
                  spectrum,
                  subblock num, blocktype,
                  sfb-wise energy.

*****************************************************************************/
INT FDKaacEnc_TnsDetect(
              TNS_DATA *tnsData,
              const TNS_CONFIG *tC,
              TNS_INFO* tnsInfo,
              INT sfbCnt,
              FIXP_DBL *spectrum,
              INT subBlockNumber,
              INT blockType
              )
{
  /* autocorrelation function for 1st, 2nd, 3rd, and 4th quarter of the spectrum. */
  FIXP_DBL rxx1[TNS_MAX_ORDER+1]; /* higher part */
  FIXP_DBL rxx2[TNS_MAX_ORDER+1]; /* lower part */
  FIXP_DBL parcor_tmp[TNS_MAX_ORDER];

  int i;

  TNS_SUBBLOCK_INFO *tsbi = (blockType == SHORT_WINDOW)
    ? &tnsData->dataRaw.Short.subBlockInfo[subBlockNumber]
    : &tnsData->dataRaw.Long.subBlockInfo;

  tnsData->filtersMerged  = FALSE;
  tsbi->tnsActive         = FALSE;
  tsbi->predictionGain    = 1000;
  tnsInfo->numOfFilters[subBlockNumber] = 0;
  tnsInfo->coefRes[subBlockNumber]      = tC->coefRes;
  for (i = 0; i < tC->maxOrder; i++) {
    tnsInfo->coef[subBlockNumber][HIFILT][i] = tnsInfo->coef[subBlockNumber][LOFILT][i] = 0;
  }

  tnsInfo->length[subBlockNumber][HIFILT] = tnsInfo->length[subBlockNumber][LOFILT] = 0;
  tnsInfo->order [subBlockNumber][HIFILT] = tnsInfo->order [subBlockNumber][LOFILT] = 0;

  if ( (tC->tnsActive) && (tC->maxOrder>0) )
  {
    int sumSqrCoef;

    FDKaacEnc_MergedAutoCorrelation(
          spectrum,
          tC->acfWindow,
          tC->lpcStartLine,
          tC->lpcStopLine,
          tC->maxOrder,
          tC->confTab.acfSplit,
          rxx1,
          rxx2);

    /* compute higher TNS filter in lattice (ParCor) form with LeRoux-Gueguen algorithm */
    tsbi->predictionGain = FDKaacEnc_AutoToParcor(rxx2, parcor_tmp, tC->confTab.tnsLimitOrder[HIFILT]);

    /* non-linear quantization of TNS lattice coefficients with given resolution */
    FDKaacEnc_Parcor2Index(
            parcor_tmp,
            tnsInfo->coef[subBlockNumber][HIFILT],
            tC->confTab.tnsLimitOrder[HIFILT],
            tC->coefRes);

    /* reduce filter order by truncating trailing zeros, compute sum(abs(coefs)) */
    for (i = tC->confTab.tnsLimitOrder[HIFILT] - 1; i >= 0; i--) {
      if (tnsInfo->coef[subBlockNumber][HIFILT][i] != 0) {
        break;
      }
    }

    tnsInfo->order[subBlockNumber][HIFILT] = i + 1;

    sumSqrCoef = 0;
    for (; i >= 0; i--) {
      sumSqrCoef += tnsInfo->coef[subBlockNumber][HIFILT][i] * tnsInfo->coef[subBlockNumber][HIFILT][i];
    }

    tnsInfo->direction[subBlockNumber][HIFILT] = tC->confTab.tnsFilterDirection[HIFILT];
    tnsInfo->length[subBlockNumber][HIFILT] = sfbCnt - tC->lpcStartBand[HIFILT];

    /* disable TNS if predictionGain is less than 3dB or sumSqrCoef is too small */
    if ((tsbi->predictionGain > tC->confTab.threshOn[HIFILT]) || (sumSqrCoef > (tC->confTab.tnsLimitOrder[HIFILT]/2 + 2)))
    {
      tsbi->tnsActive = TRUE;
      tnsInfo->numOfFilters[subBlockNumber]++;

      /* compute second filter for lower quarter; only allowed for long windows! */
      if ( (blockType != SHORT_WINDOW) &&
           (tC->confTab.filterEnabled[LOFILT]) && (tC->confTab.seperateFiltersAllowed) )
      {
        /* compute second filter for lower frequencies */

        /* compute TNS filter in lattice (ParCor) form with LeRoux-Gueguen algorithm */
        INT predGain = FDKaacEnc_AutoToParcor(rxx1, parcor_tmp, tC->confTab.tnsLimitOrder[LOFILT]);

        /* non-linear quantization of TNS lattice coefficients with given resolution */
        FDKaacEnc_Parcor2Index(
                parcor_tmp,
                tnsInfo->coef[subBlockNumber][LOFILT],
                tC->confTab.tnsLimitOrder[LOFILT],
                tC->coefRes);

        /* reduce filter order by truncating trailing zeros, compute sum(abs(coefs)) */
        for (i = tC->confTab.tnsLimitOrder[LOFILT] - 1; i >= 0; i--) {
          if (tnsInfo->coef[subBlockNumber][LOFILT][i] != 0) {
            break;
          }
        }
        tnsInfo->order[subBlockNumber][LOFILT] = i + 1;

        sumSqrCoef = 0;
        for (; i >= 0; i--) {
          sumSqrCoef += tnsInfo->coef[subBlockNumber][LOFILT][i] * tnsInfo->coef[subBlockNumber][LOFILT][i];
        }

        tnsInfo->direction[subBlockNumber][LOFILT] = tC->confTab.tnsFilterDirection[LOFILT];
        tnsInfo->length[subBlockNumber][LOFILT] = tC->lpcStartBand[HIFILT] - tC->lpcStartBand[LOFILT];

        /* filter lower quarter if gain is high enough, but not if it's too high */
        if ( ( (predGain > tC->confTab.threshOn[LOFILT]) && (predGain < (16000 * tC->confTab.tnsLimitOrder[LOFILT])) )
          || ( (sumSqrCoef > 9)  && (sumSqrCoef < 22 * tC->confTab.tnsLimitOrder[LOFILT]) ) )
        {
          /* compare lower to upper filter; if they are very similar, merge them */
          sumSqrCoef = 0;
          for (i = 0; i < tC->confTab.tnsLimitOrder[LOFILT]; i++) {
            sumSqrCoef += FDKabs(tnsInfo->coef[subBlockNumber][HIFILT][i] - tnsInfo->coef[subBlockNumber][LOFILT][i]);
          }
          if ( (sumSqrCoef < 2) &&
               (tnsInfo->direction[subBlockNumber][LOFILT] == tnsInfo->direction[subBlockNumber][HIFILT]) )
          {
            tnsData->filtersMerged = TRUE;
            tnsInfo->length[subBlockNumber][HIFILT] = sfbCnt - tC->lpcStartBand[LOFILT];
            for (; i < tnsInfo->order[subBlockNumber][HIFILT]; i++) {
              if (FDKabs(tnsInfo->coef[subBlockNumber][HIFILT][i]) > 1) {
                break;
              }
            }
            for (i--; i >= 0; i--) {
              if (tnsInfo->coef[subBlockNumber][HIFILT][i] != 0) {
                break;
              }
            }
            if (i < tnsInfo->order[subBlockNumber][HIFILT]) {
              tnsInfo->order[subBlockNumber][HIFILT] = i + 1;
            }
          }
          else {
            tnsInfo->numOfFilters[subBlockNumber]++;
          }
        } /* filter lower part */
      } /* second filter allowed  */
    } /* if predictionGain > 1437 ... */
  } /* maxOrder > 0 && tnsActive */

  return 0;

}


/***************************************************************************/
/*!
  \brief     FDKaacLdEnc_TnsSync

  synchronize TNS parameters when TNS gain difference small (relative)

  \param pointer to TNS data structure (destination)
  \param pointer to TNS data structure (source)
  \param pointer to TNS config structure
  \param number of sub-block
  \param block type

  \return void
****************************************************************************/
void FDKaacEnc_TnsSync(
             TNS_DATA *tnsDataDest,
             const TNS_DATA *tnsDataSrc,
             TNS_INFO *tnsInfoDest,
             TNS_INFO *tnsInfoSrc,
             const INT blockTypeDest,
             const INT blockTypeSrc,
             const TNS_CONFIG *tC
             )
{
  int i, w, absDiff, nWindows;
  TNS_SUBBLOCK_INFO *sbInfoDest;
  const TNS_SUBBLOCK_INFO *sbInfoSrc;

  /* if one channel contains short blocks and the other not, do not synchronize */
  if ( (blockTypeSrc == SHORT_WINDOW && blockTypeDest != SHORT_WINDOW) ||
       (blockTypeDest == SHORT_WINDOW && blockTypeSrc != SHORT_WINDOW) )
  {
    return;
  }

  if (blockTypeDest != SHORT_WINDOW) {
    sbInfoDest = &tnsDataDest->dataRaw.Long.subBlockInfo;
    sbInfoSrc  = &tnsDataSrc->dataRaw.Long.subBlockInfo;
    nWindows   = 1;
  } else {
    sbInfoDest = &tnsDataDest->dataRaw.Short.subBlockInfo[0];
    sbInfoSrc  = &tnsDataSrc->dataRaw.Short.subBlockInfo[0];
    nWindows   = 8;
  }

  for (w=0; w<nWindows; w++) {
      const TNS_SUBBLOCK_INFO *pSbInfoSrcW  = sbInfoSrc  + w;
      TNS_SUBBLOCK_INFO       *pSbInfoDestW = sbInfoDest + w;
      INT doSync = 1, absDiffSum = 0;

      /* if TNS is active in at least one channel, check if ParCor coefficients of higher filter are similar */
      if (pSbInfoDestW->tnsActive || pSbInfoSrcW->tnsActive) {
        for (i = 0; i < tC->maxOrder; i++) {
          absDiff = FDKabs(tnsInfoDest->coef[w][HIFILT][i] - tnsInfoSrc->coef[w][HIFILT][i]);
          absDiffSum += absDiff;
          /* if coefficients diverge too much between channels, do not synchronize */
          if ((absDiff > 1) || (absDiffSum > 2)) {
            doSync = 0;
            break;
          }
        }

        if (doSync) {
            /* if no significant difference was detected, synchronize coefficient sets */
            if (pSbInfoSrcW->tnsActive) {
              /* no dest filter, or more dest than source filters: use one dest filter */
              if ((!pSbInfoDestW->tnsActive) ||
                  ((pSbInfoDestW->tnsActive) && (tnsInfoDest->numOfFilters[w] > tnsInfoSrc->numOfFilters[w])))
              {
                pSbInfoDestW->tnsActive = tnsInfoDest->numOfFilters[w] = 1;
              }
              tnsDataDest->filtersMerged = tnsDataSrc->filtersMerged;
              tnsInfoDest->order       [w][HIFILT] = tnsInfoSrc->order       [w][HIFILT];
              tnsInfoDest->length      [w][HIFILT] = tnsInfoSrc->length      [w][HIFILT];
              tnsInfoDest->direction   [w][HIFILT] = tnsInfoSrc->direction   [w][HIFILT];
              tnsInfoDest->coefCompress[w][HIFILT] = tnsInfoSrc->coefCompress[w][HIFILT];

              for (i = 0; i < tC->maxOrder; i++) {
                tnsInfoDest->coef[w][HIFILT][i] = tnsInfoSrc->coef[w][HIFILT][i];
              }
            }
            else
              pSbInfoDestW->tnsActive = tnsInfoDest->numOfFilters[w] = 0;
            }
        }

    }
}

/***************************************************************************/
/*!
  \brief     FDKaacEnc_TnsEncode

  perform TNS encoding

  \param pointer to TNS info structure
  \param pointer to TNS data structure
  \param number of sfbs
  \param pointer to TNS config structure
  \param low-pass line
  \param pointer to spectrum
  \param number of sub-block
  \param block type

  \return ERROR STATUS
****************************************************************************/
INT FDKaacEnc_TnsEncode(
        TNS_INFO* tnsInfo,
        TNS_DATA* tnsData,
        const INT numOfSfb,
        const TNS_CONFIG *tC,
        const INT lowPassLine,
        FIXP_DBL* spectrum,
        const INT subBlockNumber,
        const INT blockType
        )
{
    INT i, startLine, stopLine;

    if ( ( (blockType == SHORT_WINDOW) && (!tnsData->dataRaw.Short.subBlockInfo[subBlockNumber].tnsActive) )
      || ( (blockType != SHORT_WINDOW) && (!tnsData->dataRaw.Long.subBlockInfo.tnsActive) ) )
    {
      return 1;
    }

    startLine = (tnsData->filtersMerged) ? tC->lpcStartLine[LOFILT] : tC->lpcStartLine[HIFILT];
    stopLine  = tC->lpcStopLine;

    for (i=0; i<tnsInfo->numOfFilters[subBlockNumber]; i++) {

        INT lpcGainFactor;
        FIXP_DBL LpcCoeff[TNS_MAX_ORDER];
        FIXP_DBL workBuffer[TNS_MAX_ORDER];
        FIXP_DBL parcor_tmp[TNS_MAX_ORDER];

        FDKaacEnc_Index2Parcor(
                tnsInfo->coef[subBlockNumber][i],
                parcor_tmp,
                tnsInfo->order[subBlockNumber][i],
                tC->coefRes);

        lpcGainFactor = FDKaacEnc_ParcorToLpc(
                parcor_tmp,
                LpcCoeff,
                tnsInfo->order[subBlockNumber][i],
                workBuffer);

        FDKaacEnc_AnalysisFilter(
                &spectrum[startLine],
                stopLine - startLine,
                LpcCoeff,
                tnsInfo->order[subBlockNumber][i],
                lpcGainFactor);

        /* update for second filter */
        startLine = tC->lpcStartLine[LOFILT];
        stopLine  = tC->lpcStartLine[HIFILT];
    }

    return(0);

}

static void FDKaacEnc_CalcGaussWindow(
        FIXP_DBL *win,
        const int winSize,
        const INT samplingRate,
        const INT transformResolution,
        const FIXP_DBL timeResolution,
        const INT timeResolution_e
        )
{
  #define PI_E           (2)
  #define PI_M           FL2FXCONST_DBL(3.1416f/(float)(1<<PI_E))

  #define EULER_E        (2)
  #define EULER_M        FL2FXCONST_DBL(2.7183/(float)(1<<EULER_E))

  #define COEFF_LOOP_SCALE (4)

  INT i, e1, e2, gaussExp_e;
  FIXP_DBL gaussExp_m;

  /* calc. window exponent from time resolution:
   *
   *   gaussExp = PI * samplingRate * 0.001f * timeResolution / transformResolution;
   *   gaussExp = -0.5f * gaussExp * gaussExp;
   */
  gaussExp_m = fMultNorm(timeResolution, fMult(PI_M, fDivNorm( (FIXP_DBL)(samplingRate), (FIXP_DBL)(LONG)(transformResolution*1000.f), &e1)), &e2);
  gaussExp_m = -fPow2Div2(gaussExp_m);
  gaussExp_e = 2*(e1+e2+timeResolution_e+PI_E);

  FDK_ASSERT( winSize < (1<<COEFF_LOOP_SCALE) );

  /* calc. window coefficients
   *   win[i] = (float)exp( gaussExp * (i+0.5) * (i+0.5) );
   */
  for( i=0; i<winSize; i++) {

    win[i] = fPow(
            EULER_M,
            EULER_E,
            fMult(gaussExp_m, fPow2((i*FL2FXCONST_DBL(1.f/(float)(1<<COEFF_LOOP_SCALE)) + FL2FXCONST_DBL(.5f/(float)(1<<COEFF_LOOP_SCALE))))),
            gaussExp_e + 2*COEFF_LOOP_SCALE,
           &e1);

    win[i] = scaleValueSaturate(win[i], e1);
  }
}


/***************************************************************************/
/*!
  \brief     FDKaacEnc_AutoToParcor

  conversion autocorrelation to reflection coefficients

  \param pointer to input (acf)
  \param pointer to output (reflection coefficients)
  \param number of coefficients

  \return prediction gain
****************************************************************************/
static INT FDKaacEnc_AutoToParcor(
        FIXP_DBL *RESTRICT input,
        FIXP_DBL *RESTRICT reflCoeff,
        const INT numOfCoeff
        )
{
  INT       i, j, scale=0;
  FIXP_DBL  tmp, parcorWorkBuffer[TNS_MAX_ORDER];
  INT       predictionGain = (INT)(TNS_PREDGAIN_SCALE);

  FIXP_DBL *RESTRICT workBuffer = parcorWorkBuffer;
  const FIXP_DBL  autoCorr_0 = input[0];

  if((FIXP_DBL)input[0] == FL2FXCONST_DBL(0.0)) {
    FDKmemclear(reflCoeff,numOfCoeff*sizeof(FIXP_DBL));
    return(predictionGain);
  }

  FDKmemcpy(workBuffer,&input[1],numOfCoeff*sizeof(FIXP_DBL));
  for(i=0; i<numOfCoeff; i++) {
    LONG sign = ((LONG)workBuffer[0] >> (DFRACT_BITS-1));
    tmp = (FIXP_DBL)((LONG)workBuffer[0]^sign);

    if(input[0]<tmp)
      break;

    tmp = (FIXP_DBL)((LONG)schur_div(tmp, input[0], FRACT_BITS)^(~sign));
    reflCoeff[i] = tmp;

    for(j=numOfCoeff-i-1; j>=0; j--) {
      FIXP_DBL accu1 = fMult(tmp, input[j]);
      FIXP_DBL accu2 = fMult(tmp, workBuffer[j]);
      workBuffer[j] += accu1;
      input[j] += accu2;
    }

    workBuffer++;
  }

  tmp = fMult((FIXP_DBL)((LONG)TNS_PREDGAIN_SCALE<<21), fDivNorm(fAbs(autoCorr_0), fAbs(input[0]), &scale));
  if ( fMultDiv2(autoCorr_0, input[0])<FL2FXCONST_DBL(0.0f) ) {
    tmp = -tmp;
  }
  predictionGain = (LONG)scaleValue(tmp,scale-21);

  return (predictionGain);
}


static INT FDKaacEnc_Search3(FIXP_DBL parcor)
{
  INT i, index=0;

  for(i=0;i<8;i++){
    if(parcor > FDKaacEnc_tnsCoeff3Borders[i])
      index=i;
  }
  return(index-4);
}

static INT FDKaacEnc_Search4(FIXP_DBL parcor)
{
  INT i, index=0;

  for(i=0;i<16;i++){
    if(parcor > FDKaacEnc_tnsCoeff4Borders[i])
      index=i;
  }
  return(index-8);
}


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

    functionname: FDKaacEnc_Parcor2Index

*****************************************************************************/
static void FDKaacEnc_Parcor2Index(
        const FIXP_DBL *parcor,
        INT *RESTRICT index,
        const INT order,
        const INT bitsPerCoeff
        )
{
  INT i;
  for(i=0; i<order; i++) {
    if(bitsPerCoeff == 3)
      index[i] = FDKaacEnc_Search3(parcor[i]);
    else
      index[i] = FDKaacEnc_Search4(parcor[i]);
  }
}


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

    functionname: FDKaacEnc_Index2Parcor
    description:  inverse quantization for reflection coefficients
    returns:      -
    input:        quantized values, ptr. to reflection coefficients,
                  no. of coefficients, resolution
    output:       reflection coefficients

*****************************************************************************/
static void FDKaacEnc_Index2Parcor(
        const INT *index,
        FIXP_DBL *RESTRICT parcor,
        const INT order,
        const INT bitsPerCoeff
        )
{
  INT i;
  for(i=0; i<order; i++)
    parcor[i] = bitsPerCoeff == 4 ? FDKaacEnc_tnsEncCoeff4[index[i]+8] : FDKaacEnc_tnsEncCoeff3[index[i]+4];
}


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

    functionname: FDKaacEnc_ParcorToLpc
    description:  conversion reflection coefficients to LPC coefficients
    returns:      Gain factor
    input:        reflection coefficients, no. of reflection coefficients <order>,
                  ptr. to work buffer (required size: order)
    output:       <order> LPC coefficients

*****************************************************************************/
static INT FDKaacEnc_ParcorToLpc(
        const FIXP_DBL *reflCoeff,
        FIXP_DBL *RESTRICT LpcCoeff,
        const INT numOfCoeff,
        FIXP_DBL *RESTRICT workBuffer
        )
{
  INT i, j;
  INT shiftval, par2LpcShiftVal = 6;  /* 6 should be enough, bec. max(numOfCoeff) = 20 */
  FIXP_DBL maxVal = FL2FXCONST_DBL(0.0f);

  LpcCoeff[0] = reflCoeff[0] >> par2LpcShiftVal;
  for(i=1; i<numOfCoeff; i++) {
    for(j=0; j<i; j++) {
        workBuffer[j] = LpcCoeff[i-1-j];
    }

    for(j=0; j<i; j++) {
        LpcCoeff[j] += fMult(reflCoeff[i],workBuffer[j]);
    }

    LpcCoeff[i] = reflCoeff[i] >> par2LpcShiftVal;
  }

  /* normalize LpcCoeff and calc shiftfactor */
  for(i=0; i<numOfCoeff; i++) {
      maxVal = fixMax(maxVal,(FIXP_DBL)fixp_abs(LpcCoeff[i]));
  }

  shiftval = CountLeadingBits(maxVal);
  shiftval = (shiftval>=par2LpcShiftVal) ? par2LpcShiftVal : shiftval;

  for(i=0; i<numOfCoeff; i++)
      LpcCoeff[i] = LpcCoeff[i]<<shiftval;

  return (par2LpcShiftVal - shiftval);
}

/***************************************************************************/
/*!
  \brief     FDKaacEnc_AnalysisFilter

  TNS analysis filter (all-zero filter)

  \param pointer to signal spectrum
  \param number of lines
  \param pointer to lpc coefficients
  \param filter order
  \param lpc gain factor

  \return void
****************************************************************************/
/* Note: in-place computation possible */
static void FDKaacEnc_AnalysisFilter(
        FIXP_DBL *RESTRICT signal,
        const INT numOfLines,
        const FIXP_DBL *predictorCoeff,
        const INT order,
        const INT lpcGainFactor
        )
{
  FIXP_DBL statusVar[TNS_MAX_ORDER];
  INT i, j;
  const INT shift = lpcGainFactor + 1;      /* +1, because fMultDiv2 */
  FIXP_DBL tmp;

  if (order>0) {

    INT idx = 0;

    /* keep filter coefficients twice and save memory copy operation in
       modulo state buffer */
#if defined(ARCH_PREFER_MULT_32x16)
    FIXP_SGL  coeff[2*TNS_MAX_ORDER];
    const FIXP_SGL *pCoeff;
    for(i=0;i<order;i++) {
      coeff[i]       = FX_DBL2FX_SGL(predictorCoeff[i]);
    }
    FDKmemcpy(&coeff[order], coeff, order*sizeof(FIXP_SGL));
#else
    FIXP_DBL  coeff[2*TNS_MAX_ORDER];
    const FIXP_DBL *pCoeff;
    FDKmemcpy(&coeff[0],     predictorCoeff, order*sizeof(FIXP_DBL));
    FDKmemcpy(&coeff[order], predictorCoeff, order*sizeof(FIXP_DBL));
#endif
    FDKmemclear(statusVar, order*sizeof(FIXP_DBL));

    for(j=0; j<numOfLines; j++) {
      pCoeff = &coeff[(order-idx)];
      tmp = FL2FXCONST_DBL(0);
      for(i=0; i<order; i++) {
          tmp = fMultAddDiv2(tmp, pCoeff[i], statusVar[i]) ;
      }

      if(--idx<0) { idx = order-1; }
      statusVar[idx] = signal[j];

      FDK_ASSERT(lpcGainFactor>=0);
      signal[j] = (tmp<<shift) + signal[j];
    }
  }
}