Line data    Source code

       1             : /***********************************************************************
       2             : Copyright (c) 2006-2011, Skype Limited. All rights reserved.
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      15             : THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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      26             : ***********************************************************************/
      27             : 
      28             : #ifdef HAVE_CONFIG_H
      29             : #include "config.h"
      30             : #endif
      31             : 
      32             : #include "SigProc_FIX.h"
      33             : #include "SigProc_FLP.h"
      34             : #include "define.h"
      35             : 
      36             : /* compute inverse of LPC prediction gain, and                          */
      37             : /* test if LPC coefficients are stable (all poles within unit circle)   */
      38             : /* this code is based on silk_a2k_FLP()                                 */
      39           0 : silk_float silk_LPC_inverse_pred_gain_FLP(  /* O    return inverse prediction gain, energy domain               */
      40             :     const silk_float    *A,                 /* I    prediction coefficients [order]                             */
      41             :     opus_int32          order               /* I    prediction order                                            */
      42             : )
      43             : {
      44             :     opus_int   k, n;
      45             :     double     invGain, rc, rc_mult1, rc_mult2, tmp1, tmp2;
      46             :     silk_float Atmp[ SILK_MAX_ORDER_LPC ];
      47             : 
      48           0 :     silk_memcpy( Atmp, A, order * sizeof(silk_float) );
      49             : 
      50           0 :     invGain = 1.0;
      51           0 :     for( k = order - 1; k > 0; k-- ) {
      52           0 :         rc = -Atmp[ k ];
      53           0 :         rc_mult1 = 1.0f - rc * rc;
      54           0 :         invGain *= rc_mult1;
      55           0 :         if( invGain * MAX_PREDICTION_POWER_GAIN < 1.0f ) {
      56           0 :             return 0.0f;
      57             :         }
      58           0 :         rc_mult2 = 1.0f / rc_mult1;
      59           0 :         for( n = 0; n < (k + 1) >> 1; n++ ) {
      60           0 :             tmp1 = Atmp[ n ];
      61           0 :             tmp2 = Atmp[ k - n - 1 ];
      62           0 :             Atmp[ n ]         = (silk_float)( ( tmp1 - tmp2 * rc ) * rc_mult2 );
      63           0 :             Atmp[ k - n - 1 ] = (silk_float)( ( tmp2 - tmp1 * rc ) * rc_mult2 );
      64             :         }
      65             :     }
      66           0 :     rc = -Atmp[ 0 ];
      67           0 :     rc_mult1 = 1.0f - rc * rc;
      68           0 :     invGain *= rc_mult1;
      69           0 :     if( invGain * MAX_PREDICTION_POWER_GAIN < 1.0f ) {
      70           0 :         return 0.0f;
      71             :     }
      72           0 :     return (silk_float)invGain;
      73             : }