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      1 /*
      2  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
      3  *
      4  *  Use of this source code is governed by a BSD-style license
      5  *  that can be found in the LICENSE file in the root of the source
      6  *  tree. An additional intellectual property rights grant can be found
      7  *  in the file PATENTS.  All contributing project authors may
      8  *  be found in the AUTHORS file in the root of the source tree.
      9  */
     10 
     11 #include "webrtc_cng.h"
     12 
     13 #include <string.h>
     14 #include <stdlib.h>
     15 
     16 #include "cng_helpfuns.h"
     17 #include "signal_processing_library.h"
     18 
     19 typedef struct WebRtcCngDecoder_ {
     20   uint32_t dec_seed;
     21   int32_t dec_target_energy;
     22   int32_t dec_used_energy;
     23   int16_t dec_target_reflCoefs[WEBRTC_CNG_MAX_LPC_ORDER + 1];
     24   int16_t dec_used_reflCoefs[WEBRTC_CNG_MAX_LPC_ORDER + 1];
     25   int16_t dec_filtstate[WEBRTC_CNG_MAX_LPC_ORDER + 1];
     26   int16_t dec_filtstateLow[WEBRTC_CNG_MAX_LPC_ORDER + 1];
     27   int16_t dec_Efiltstate[WEBRTC_CNG_MAX_LPC_ORDER + 1];
     28   int16_t dec_EfiltstateLow[WEBRTC_CNG_MAX_LPC_ORDER + 1];
     29   int16_t dec_order;
     30   int16_t dec_target_scale_factor;  /* Q29 */
     31   int16_t dec_used_scale_factor;  /* Q29 */
     32   int16_t target_scale_factor;  /* Q13 */
     33   int16_t errorcode;
     34   int16_t initflag;
     35 } WebRtcCngDecoder;
     36 
     37 typedef struct WebRtcCngEncoder_ {
     38   size_t enc_nrOfCoefs;
     39   int enc_sampfreq;
     40   int16_t enc_interval;
     41   int16_t enc_msSinceSID;
     42   int32_t enc_Energy;
     43   int16_t enc_reflCoefs[WEBRTC_CNG_MAX_LPC_ORDER + 1];
     44   int32_t enc_corrVector[WEBRTC_CNG_MAX_LPC_ORDER + 1];
     45   uint32_t enc_seed;
     46   int16_t errorcode;
     47   int16_t initflag;
     48 } WebRtcCngEncoder;
     49 
     50 const int32_t WebRtcCng_kDbov[94] = {
     51   1081109975,  858756178,  682134279,  541838517,  430397633,  341876992,
     52   271562548,  215709799,  171344384,  136103682,  108110997,   85875618,
     53   68213428,   54183852,   43039763,   34187699,   27156255,   21570980,
     54   17134438,   13610368,   10811100,    8587562,    6821343,    5418385,
     55   4303976,    3418770,    2715625,    2157098,    1713444,    1361037,
     56   1081110,     858756,     682134,     541839,     430398,     341877,
     57   271563,     215710,     171344,     136104,     108111,      85876,
     58   68213,      54184,      43040,      34188,      27156,      21571,
     59   17134,      13610,      10811,       8588,       6821,       5418,
     60   4304,       3419,       2716,       2157,       1713,       1361,
     61   1081,        859,        682,        542,        430,        342,
     62   272,        216,        171,        136,        108,         86,
     63   68,         54,         43,         34,         27,         22,
     64   17,         14,         11,          9,          7,          5,
     65   4,          3,          3,          2,          2,           1,
     66   1,          1,          1,          1
     67 };
     68 
     69 const int16_t WebRtcCng_kCorrWindow[WEBRTC_CNG_MAX_LPC_ORDER] = {
     70   32702, 32636, 32570, 32505, 32439, 32374,
     71   32309, 32244, 32179, 32114, 32049, 31985
     72 };
     73 
     74 /****************************************************************************
     75  * WebRtcCng_CreateEnc/Dec(...)
     76  *
     77  * These functions create an instance to the specified structure
     78  *
     79  * Input:
     80  *      - XXX_inst      : Pointer to created instance that should be created
     81  *
     82  * Return value         :  0 - Ok
     83  *                        -1 - Error
     84  */
     85 int16_t WebRtcCng_CreateEnc(CNG_enc_inst** cng_inst) {
     86   if (cng_inst != NULL) {
     87     *cng_inst = (CNG_enc_inst*) malloc(sizeof(WebRtcCngEncoder));
     88     if (*cng_inst != NULL) {
     89       (*(WebRtcCngEncoder**) cng_inst)->errorcode = 0;
     90       (*(WebRtcCngEncoder**) cng_inst)->initflag = 0;
     91 
     92       /* Needed to get the right function pointers in SPLIB. */
     93       WebRtcSpl_Init();
     94 
     95       return 0;
     96     } else {
     97       /* The memory could not be allocated. */
     98       return -1;
     99     }
    100   } else {
    101     /* The input pointer is invalid (NULL). */
    102     return -1;
    103   }
    104 }
    105 
    106 int16_t WebRtcCng_CreateDec(CNG_dec_inst** cng_inst) {
    107   if (cng_inst != NULL ) {
    108     *cng_inst = (CNG_dec_inst*) malloc(sizeof(WebRtcCngDecoder));
    109     if (*cng_inst != NULL ) {
    110       (*(WebRtcCngDecoder**) cng_inst)->errorcode = 0;
    111       (*(WebRtcCngDecoder**) cng_inst)->initflag = 0;
    112 
    113       /* Needed to get the right function pointers in SPLIB. */
    114       WebRtcSpl_Init();
    115 
    116       return 0;
    117     } else {
    118       /* The memory could not be allocated */
    119       return -1;
    120     }
    121   } else {
    122     /* The input pointer is invalid (NULL). */
    123     return -1;
    124   }
    125 }
    126 
    127 /****************************************************************************
    128  * WebRtcCng_InitEnc/Dec(...)
    129  *
    130  * This function initializes a instance
    131  *
    132  * Input:
    133  *    - cng_inst      : Instance that should be initialized
    134  *
    135  *    - fs            : 8000 for narrowband and 16000 for wideband
    136  *    - interval      : generate SID data every interval ms
    137  *    - quality       : TBD
    138  *
    139  * Output:
    140  *    - cng_inst      : Initialized instance
    141  *
    142  * Return value       :  0 - Ok
    143  *                      -1 - Error
    144  */
    145 int WebRtcCng_InitEnc(CNG_enc_inst* cng_inst, int fs, int16_t interval,
    146                       int16_t quality) {
    147   int i;
    148   WebRtcCngEncoder* inst = (WebRtcCngEncoder*) cng_inst;
    149   memset(inst, 0, sizeof(WebRtcCngEncoder));
    150 
    151   /* Check LPC order */
    152   if (quality > WEBRTC_CNG_MAX_LPC_ORDER || quality <= 0) {
    153     inst->errorcode = CNG_DISALLOWED_LPC_ORDER;
    154     return -1;
    155   }
    156 
    157   inst->enc_sampfreq = fs;
    158   inst->enc_interval = interval;
    159   inst->enc_nrOfCoefs = quality;
    160   inst->enc_msSinceSID = 0;
    161   inst->enc_seed = 7777;  /* For debugging only. */
    162   inst->enc_Energy = 0;
    163   for (i = 0; i < (WEBRTC_CNG_MAX_LPC_ORDER + 1); i++) {
    164     inst->enc_reflCoefs[i] = 0;
    165     inst->enc_corrVector[i] = 0;
    166   }
    167   inst->initflag = 1;
    168 
    169   return 0;
    170 }
    171 
    172 void WebRtcCng_InitDec(CNG_dec_inst* cng_inst) {
    173   int i;
    174 
    175   WebRtcCngDecoder* inst = (WebRtcCngDecoder*) cng_inst;
    176 
    177   memset(inst, 0, sizeof(WebRtcCngDecoder));
    178   inst->dec_seed = 7777;  /* For debugging only. */
    179   inst->dec_order = 5;
    180   inst->dec_target_scale_factor = 0;
    181   inst->dec_used_scale_factor = 0;
    182   for (i = 0; i < (WEBRTC_CNG_MAX_LPC_ORDER + 1); i++) {
    183     inst->dec_filtstate[i] = 0;
    184     inst->dec_target_reflCoefs[i] = 0;
    185     inst->dec_used_reflCoefs[i] = 0;
    186   }
    187   inst->dec_target_reflCoefs[0] = 0;
    188   inst->dec_used_reflCoefs[0] = 0;
    189   inst->dec_used_energy = 0;
    190   inst->initflag = 1;
    191 }
    192 
    193 /****************************************************************************
    194  * WebRtcCng_FreeEnc/Dec(...)
    195  *
    196  * These functions frees the dynamic memory of a specified instance
    197  *
    198  * Input:
    199  *    - cng_inst      : Pointer to created instance that should be freed
    200  *
    201  * Return value       :  0 - Ok
    202  *                      -1 - Error
    203  */
    204 int16_t WebRtcCng_FreeEnc(CNG_enc_inst* cng_inst) {
    205   free(cng_inst);
    206   return 0;
    207 }
    208 
    209 int16_t WebRtcCng_FreeDec(CNG_dec_inst* cng_inst) {
    210   free(cng_inst);
    211   return 0;
    212 }
    213 
    214 /****************************************************************************
    215  * WebRtcCng_Encode(...)
    216  *
    217  * These functions analyzes background noise
    218  *
    219  * Input:
    220  *    - cng_inst      : Pointer to created instance
    221  *    - speech        : Signal (noise) to be analyzed
    222  *    - nrOfSamples   : Size of speech vector
    223  *    - bytesOut      : Nr of bytes to transmit, might be 0
    224  *
    225  * Return value       :  0 - Ok
    226  *                      -1 - Error
    227  */
    228 int WebRtcCng_Encode(CNG_enc_inst* cng_inst, int16_t* speech,
    229                      size_t nrOfSamples, uint8_t* SIDdata,
    230                      size_t* bytesOut, int16_t forceSID) {
    231   WebRtcCngEncoder* inst = (WebRtcCngEncoder*) cng_inst;
    232 
    233   int16_t arCoefs[WEBRTC_CNG_MAX_LPC_ORDER + 1];
    234   int32_t corrVector[WEBRTC_CNG_MAX_LPC_ORDER + 1];
    235   int16_t refCs[WEBRTC_CNG_MAX_LPC_ORDER + 1];
    236   int16_t hanningW[WEBRTC_CNG_MAX_OUTSIZE_ORDER];
    237   int16_t ReflBeta = 19661;  /* 0.6 in q15. */
    238   int16_t ReflBetaComp = 13107;  /* 0.4 in q15. */
    239   int32_t outEnergy;
    240   int outShifts;
    241   size_t i;
    242   int stab;
    243   int acorrScale;
    244   size_t index;
    245   size_t ind, factor;
    246   int32_t* bptr;
    247   int32_t blo, bhi;
    248   int16_t negate;
    249   const int16_t* aptr;
    250   int16_t speechBuf[WEBRTC_CNG_MAX_OUTSIZE_ORDER];
    251 
    252   /* Check if encoder initiated. */
    253   if (inst->initflag != 1) {
    254     inst->errorcode = CNG_ENCODER_NOT_INITIATED;
    255     return -1;
    256   }
    257 
    258   /* Check framesize. */
    259   if (nrOfSamples > WEBRTC_CNG_MAX_OUTSIZE_ORDER) {
    260     inst->errorcode = CNG_DISALLOWED_FRAME_SIZE;
    261     return -1;
    262   }
    263 
    264   for (i = 0; i < nrOfSamples; i++) {
    265     speechBuf[i] = speech[i];
    266   }
    267 
    268   factor = nrOfSamples;
    269 
    270   /* Calculate energy and a coefficients. */
    271   outEnergy = WebRtcSpl_Energy(speechBuf, nrOfSamples, &outShifts);
    272   while (outShifts > 0) {
    273     /* We can only do 5 shifts without destroying accuracy in
    274      * division factor. */
    275     if (outShifts > 5) {
    276       outEnergy <<= (outShifts - 5);
    277       outShifts = 5;
    278     } else {
    279       factor /= 2;
    280       outShifts--;
    281     }
    282   }
    283   outEnergy = WebRtcSpl_DivW32W16(outEnergy, (int16_t)factor);
    284 
    285   if (outEnergy > 1) {
    286     /* Create Hanning Window. */
    287     WebRtcSpl_GetHanningWindow(hanningW, nrOfSamples / 2);
    288     for (i = 0; i < (nrOfSamples / 2); i++)
    289       hanningW[nrOfSamples - i - 1] = hanningW[i];
    290 
    291     WebRtcSpl_ElementwiseVectorMult(speechBuf, hanningW, speechBuf, nrOfSamples,
    292                                     14);
    293 
    294     WebRtcSpl_AutoCorrelation(speechBuf, nrOfSamples, inst->enc_nrOfCoefs,
    295                               corrVector, &acorrScale);
    296 
    297     if (*corrVector == 0)
    298       *corrVector = WEBRTC_SPL_WORD16_MAX;
    299 
    300     /* Adds the bandwidth expansion. */
    301     aptr = WebRtcCng_kCorrWindow;
    302     bptr = corrVector;
    303 
    304     /* (zzz) lpc16_1 = 17+1+820+2+2 = 842 (ordo2=700). */
    305     for (ind = 0; ind < inst->enc_nrOfCoefs; ind++) {
    306       /* The below code multiplies the 16 b corrWindow values (Q15) with
    307        * the 32 b corrvector (Q0) and shifts the result down 15 steps. */
    308       negate = *bptr < 0;
    309       if (negate)
    310         *bptr = -*bptr;
    311 
    312       blo = (int32_t) * aptr * (*bptr & 0xffff);
    313       bhi = ((blo >> 16) & 0xffff)
    314           + ((int32_t)(*aptr++) * ((*bptr >> 16) & 0xffff));
    315       blo = (blo & 0xffff) | ((bhi & 0xffff) << 16);
    316 
    317       *bptr = (((bhi >> 16) & 0x7fff) << 17) | ((uint32_t) blo >> 15);
    318       if (negate)
    319         *bptr = -*bptr;
    320       bptr++;
    321     }
    322     /* End of bandwidth expansion. */
    323 
    324     stab = WebRtcSpl_LevinsonDurbin(corrVector, arCoefs, refCs,
    325                                     inst->enc_nrOfCoefs);
    326 
    327     if (!stab) {
    328       /* Disregard from this frame */
    329       *bytesOut = 0;
    330       return 0;
    331     }
    332 
    333   } else {
    334     for (i = 0; i < inst->enc_nrOfCoefs; i++)
    335       refCs[i] = 0;
    336   }
    337 
    338   if (forceSID) {
    339     /* Read instantaneous values instead of averaged. */
    340     for (i = 0; i < inst->enc_nrOfCoefs; i++)
    341       inst->enc_reflCoefs[i] = refCs[i];
    342     inst->enc_Energy = outEnergy;
    343   } else {
    344     /* Average history with new values. */
    345     for (i = 0; i < (inst->enc_nrOfCoefs); i++) {
    346       inst->enc_reflCoefs[i] = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(
    347           inst->enc_reflCoefs[i], ReflBeta, 15);
    348       inst->enc_reflCoefs[i] += (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(
    349           refCs[i], ReflBetaComp, 15);
    350     }
    351     inst->enc_Energy = (outEnergy >> 2) + (inst->enc_Energy >> 1)
    352         + (inst->enc_Energy >> 2);
    353   }
    354 
    355   if (inst->enc_Energy < 1) {
    356     inst->enc_Energy = 1;
    357   }
    358 
    359   if ((inst->enc_msSinceSID > (inst->enc_interval - 1)) || forceSID) {
    360 
    361     /* Search for best dbov value. */
    362     index = 0;
    363     for (i = 1; i < 93; i++) {
    364       /* Always round downwards. */
    365       if ((inst->enc_Energy - WebRtcCng_kDbov[i]) > 0) {
    366         index = i;
    367         break;
    368       }
    369     }
    370     if ((i == 93) && (index == 0))
    371       index = 94;
    372     SIDdata[0] = (uint8_t)index;
    373 
    374     /* Quantize coefficients with tweak for WebRtc implementation of RFC3389. */
    375     if (inst->enc_nrOfCoefs == WEBRTC_CNG_MAX_LPC_ORDER) {
    376       for (i = 0; i < inst->enc_nrOfCoefs; i++) {
    377         /* Q15 to Q7 with rounding. */
    378         SIDdata[i + 1] = ((inst->enc_reflCoefs[i] + 128) >> 8);
    379       }
    380     } else {
    381       for (i = 0; i < inst->enc_nrOfCoefs; i++) {
    382         /* Q15 to Q7 with rounding. */
    383         SIDdata[i + 1] = (127 + ((inst->enc_reflCoefs[i] + 128) >> 8));
    384       }
    385     }
    386 
    387     inst->enc_msSinceSID = 0;
    388     *bytesOut = inst->enc_nrOfCoefs + 1;
    389 
    390     inst->enc_msSinceSID +=
    391         (int16_t)((1000 * nrOfSamples) / inst->enc_sampfreq);
    392     return (int)(inst->enc_nrOfCoefs + 1);
    393   } else {
    394     inst->enc_msSinceSID +=
    395         (int16_t)((1000 * nrOfSamples) / inst->enc_sampfreq);
    396     *bytesOut = 0;
    397     return 0;
    398   }
    399 }
    400 
    401 /****************************************************************************
    402  * WebRtcCng_UpdateSid(...)
    403  *
    404  * These functions updates the CN state, when a new SID packet arrives
    405  *
    406  * Input:
    407  *    - cng_inst      : Pointer to created instance that should be freed
    408  *    - SID           : SID packet, all headers removed
    409  *    - length        : Length in bytes of SID packet
    410  *
    411  * Return value       :  0 - Ok
    412  *                      -1 - Error
    413  */
    414 int16_t WebRtcCng_UpdateSid(CNG_dec_inst* cng_inst, uint8_t* SID,
    415                             size_t length) {
    416 
    417   WebRtcCngDecoder* inst = (WebRtcCngDecoder*) cng_inst;
    418   int16_t refCs[WEBRTC_CNG_MAX_LPC_ORDER];
    419   int32_t targetEnergy;
    420   int i;
    421 
    422   if (inst->initflag != 1) {
    423     inst->errorcode = CNG_DECODER_NOT_INITIATED;
    424     return -1;
    425   }
    426 
    427   /* Throw away reflection coefficients of higher order than we can handle. */
    428   if (length > (WEBRTC_CNG_MAX_LPC_ORDER + 1))
    429     length = WEBRTC_CNG_MAX_LPC_ORDER + 1;
    430 
    431   inst->dec_order = (int16_t)length - 1;
    432 
    433   if (SID[0] > 93)
    434     SID[0] = 93;
    435   targetEnergy = WebRtcCng_kDbov[SID[0]];
    436   /* Take down target energy to 75%. */
    437   targetEnergy = targetEnergy >> 1;
    438   targetEnergy += targetEnergy >> 2;
    439 
    440   inst->dec_target_energy = targetEnergy;
    441 
    442   /* Reconstruct coeffs with tweak for WebRtc implementation of RFC3389. */
    443   if (inst->dec_order == WEBRTC_CNG_MAX_LPC_ORDER) {
    444     for (i = 0; i < (inst->dec_order); i++) {
    445       refCs[i] = SID[i + 1] << 8; /* Q7 to Q15*/
    446       inst->dec_target_reflCoefs[i] = refCs[i];
    447     }
    448   } else {
    449     for (i = 0; i < (inst->dec_order); i++) {
    450       refCs[i] = (SID[i + 1] - 127) << 8; /* Q7 to Q15. */
    451       inst->dec_target_reflCoefs[i] = refCs[i];
    452     }
    453   }
    454 
    455   for (i = (inst->dec_order); i < WEBRTC_CNG_MAX_LPC_ORDER; i++) {
    456     refCs[i] = 0;
    457     inst->dec_target_reflCoefs[i] = refCs[i];
    458   }
    459 
    460   return 0;
    461 }
    462 
    463 /****************************************************************************
    464  * WebRtcCng_Generate(...)
    465  *
    466  * These functions generates CN data when needed
    467  *
    468  * Input:
    469  *    - cng_inst      : Pointer to created instance that should be freed
    470  *    - outData       : pointer to area to write CN data
    471  *    - nrOfSamples   : How much data to generate
    472  *
    473  * Return value        :  0 - Ok
    474  *                       -1 - Error
    475  */
    476 int16_t WebRtcCng_Generate(CNG_dec_inst* cng_inst, int16_t* outData,
    477                            size_t nrOfSamples, int16_t new_period) {
    478   WebRtcCngDecoder* inst = (WebRtcCngDecoder*) cng_inst;
    479 
    480   size_t i;
    481   int16_t excitation[WEBRTC_CNG_MAX_OUTSIZE_ORDER];
    482   int16_t low[WEBRTC_CNG_MAX_OUTSIZE_ORDER];
    483   int16_t lpPoly[WEBRTC_CNG_MAX_LPC_ORDER + 1];
    484   int16_t ReflBetaStd = 26214;  /* 0.8 in q15. */
    485   int16_t ReflBetaCompStd = 6553;  /* 0.2 in q15. */
    486   int16_t ReflBetaNewP = 19661;  /* 0.6 in q15. */
    487   int16_t ReflBetaCompNewP = 13107;  /* 0.4 in q15. */
    488   int16_t Beta, BetaC, tmp1, tmp2, tmp3;
    489   int32_t targetEnergy;
    490   int16_t En;
    491   int16_t temp16;
    492 
    493   if (nrOfSamples > WEBRTC_CNG_MAX_OUTSIZE_ORDER) {
    494     inst->errorcode = CNG_DISALLOWED_FRAME_SIZE;
    495     return -1;
    496   }
    497 
    498   if (new_period) {
    499     inst->dec_used_scale_factor = inst->dec_target_scale_factor;
    500     Beta = ReflBetaNewP;
    501     BetaC = ReflBetaCompNewP;
    502   } else {
    503     Beta = ReflBetaStd;
    504     BetaC = ReflBetaCompStd;
    505   }
    506 
    507   /* Here we use a 0.5 weighting, should possibly be modified to 0.6. */
    508   tmp1 = inst->dec_used_scale_factor << 2; /* Q13->Q15 */
    509   tmp2 = inst->dec_target_scale_factor << 2; /* Q13->Q15 */
    510   tmp3 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(tmp1, Beta, 15);
    511   tmp3 += (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(tmp2, BetaC, 15);
    512   inst->dec_used_scale_factor = tmp3 >> 2; /* Q15->Q13 */
    513 
    514   inst->dec_used_energy = inst->dec_used_energy >> 1;
    515   inst->dec_used_energy += inst->dec_target_energy >> 1;
    516 
    517   /* Do the same for the reflection coeffs. */
    518   for (i = 0; i < WEBRTC_CNG_MAX_LPC_ORDER; i++) {
    519     inst->dec_used_reflCoefs[i] = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(
    520         inst->dec_used_reflCoefs[i], Beta, 15);
    521     inst->dec_used_reflCoefs[i] += (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(
    522         inst->dec_target_reflCoefs[i], BetaC, 15);
    523   }
    524 
    525   /* Compute the polynomial coefficients. */
    526   WebRtcCng_K2a16(inst->dec_used_reflCoefs, WEBRTC_CNG_MAX_LPC_ORDER, lpPoly);
    527 
    528 
    529   targetEnergy = inst->dec_used_energy;
    530 
    531   /* Calculate scaling factor based on filter energy. */
    532   En = 8192;  /* 1.0 in Q13. */
    533   for (i = 0; i < (WEBRTC_CNG_MAX_LPC_ORDER); i++) {
    534 
    535     /* Floating point value for reference.
    536        E *= 1.0 - (inst->dec_used_reflCoefs[i] / 32768.0) *
    537        (inst->dec_used_reflCoefs[i] / 32768.0);
    538      */
    539 
    540     /* Same in fixed point. */
    541     /* K(i).^2 in Q15. */
    542     temp16 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(
    543         inst->dec_used_reflCoefs[i], inst->dec_used_reflCoefs[i], 15);
    544     /* 1 - K(i).^2 in Q15. */
    545     temp16 = 0x7fff - temp16;
    546     En = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(En, temp16, 15);
    547   }
    548 
    549   /* float scaling= sqrt(E * inst->dec_target_energy / (1 << 24)); */
    550 
    551   /* Calculate sqrt(En * target_energy / excitation energy) */
    552   targetEnergy = WebRtcSpl_Sqrt(inst->dec_used_energy);
    553 
    554   En = (int16_t) WebRtcSpl_Sqrt(En) << 6;
    555   En = (En * 3) >> 1;  /* 1.5 estimates sqrt(2). */
    556   inst->dec_used_scale_factor = (int16_t)((En * targetEnergy) >> 12);
    557 
    558   /* Generate excitation. */
    559   /* Excitation energy per sample is 2.^24 - Q13 N(0,1). */
    560   for (i = 0; i < nrOfSamples; i++) {
    561     excitation[i] = WebRtcSpl_RandN(&inst->dec_seed) >> 1;
    562   }
    563 
    564   /* Scale to correct energy. */
    565   WebRtcSpl_ScaleVector(excitation, excitation, inst->dec_used_scale_factor,
    566                         nrOfSamples, 13);
    567 
    568   /* |lpPoly| - Coefficients in Q12.
    569    * |excitation| - Speech samples.
    570    * |nst->dec_filtstate| - State preservation.
    571    * |outData| - Filtered speech samples. */
    572   WebRtcSpl_FilterAR(lpPoly, WEBRTC_CNG_MAX_LPC_ORDER + 1, excitation,
    573                      nrOfSamples, inst->dec_filtstate, WEBRTC_CNG_MAX_LPC_ORDER,
    574                      inst->dec_filtstateLow, WEBRTC_CNG_MAX_LPC_ORDER, outData,
    575                      low, nrOfSamples);
    576 
    577   return 0;
    578 }
    579 
    580 /****************************************************************************
    581  * WebRtcCng_GetErrorCodeEnc/Dec(...)
    582  *
    583  * This functions can be used to check the error code of a CNG instance. When
    584  * a function returns -1 a error code will be set for that instance. The
    585  * function below extract the code of the last error that occured in the
    586  * specified instance.
    587  *
    588  * Input:
    589  *    - CNG_inst    : CNG enc/dec instance
    590  *
    591  * Return value     : Error code
    592  */
    593 int16_t WebRtcCng_GetErrorCodeEnc(CNG_enc_inst* cng_inst) {
    594   /* Typecast pointer to real structure. */
    595   WebRtcCngEncoder* inst = (WebRtcCngEncoder*) cng_inst;
    596   return inst->errorcode;
    597 }
    598 
    599 int16_t WebRtcCng_GetErrorCodeDec(CNG_dec_inst* cng_inst) {
    600   /* Typecast pointer to real structure. */
    601   WebRtcCngDecoder* inst = (WebRtcCngDecoder*) cng_inst;
    602   return inst->errorcode;
    603 }
    604