Chris@69: /***********************************************************************
Chris@69: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
Chris@69: Redistribution and use in source and binary forms, with or without
Chris@69: modification, are permitted provided that the following conditions
Chris@69: are met:
Chris@69: - Redistributions of source code must retain the above copyright notice,
Chris@69: this list of conditions and the following disclaimer.
Chris@69: - Redistributions in binary form must reproduce the above copyright
Chris@69: notice, this list of conditions and the following disclaimer in the
Chris@69: documentation and/or other materials provided with the distribution.
Chris@69: - Neither the name of Internet Society, IETF or IETF Trust, nor the
Chris@69: names of specific contributors, may be used to endorse or promote
Chris@69: products derived from this software without specific prior written
Chris@69: permission.
Chris@69: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
Chris@69: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
Chris@69: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
Chris@69: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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Chris@69: POSSIBILITY OF SUCH DAMAGE.
Chris@69: ***********************************************************************/
Chris@69: 
Chris@69: #ifdef HAVE_CONFIG_H
Chris@69: #include "config.h"
Chris@69: #endif
Chris@69: 
Chris@69: #include "SigProc_FIX.h"
Chris@69: #include "SigProc_FLP.h"
Chris@69: #include "define.h"
Chris@69: 
Chris@69: /* compute inverse of LPC prediction gain, and                          */
Chris@69: /* test if LPC coefficients are stable (all poles within unit circle)   */
Chris@69: /* this code is based on silk_a2k_FLP()                                 */
Chris@69: silk_float silk_LPC_inverse_pred_gain_FLP(  /* O    return inverse prediction gain, energy domain               */
Chris@69:     const silk_float    *A,                 /* I    prediction coefficients [order]                             */
Chris@69:     opus_int32          order               /* I    prediction order                                            */
Chris@69: )
Chris@69: {
Chris@69:     opus_int   k, n;
Chris@69:     double     invGain, rc, rc_mult1, rc_mult2, tmp1, tmp2;
Chris@69:     silk_float Atmp[ SILK_MAX_ORDER_LPC ];
Chris@69: 
Chris@69:     silk_memcpy( Atmp, A, order * sizeof(silk_float) );
Chris@69: 
Chris@69:     invGain = 1.0;
Chris@69:     for( k = order - 1; k > 0; k-- ) {
Chris@69:         rc = -Atmp[ k ];
Chris@69:         rc_mult1 = 1.0f - rc * rc;
Chris@69:         invGain *= rc_mult1;
Chris@69:         if( invGain * MAX_PREDICTION_POWER_GAIN < 1.0f ) {
Chris@69:             return 0.0f;
Chris@69:         }
Chris@69:         rc_mult2 = 1.0f / rc_mult1;
Chris@69:         for( n = 0; n < (k + 1) >> 1; n++ ) {
Chris@69:             tmp1 = Atmp[ n ];
Chris@69:             tmp2 = Atmp[ k - n - 1 ];
Chris@69:             Atmp[ n ]         = (silk_float)( ( tmp1 - tmp2 * rc ) * rc_mult2 );
Chris@69:             Atmp[ k - n - 1 ] = (silk_float)( ( tmp2 - tmp1 * rc ) * rc_mult2 );
Chris@69:         }
Chris@69:     }
Chris@69:     rc = -Atmp[ 0 ];
Chris@69:     rc_mult1 = 1.0f - rc * rc;
Chris@69:     invGain *= rc_mult1;
Chris@69:     if( invGain * MAX_PREDICTION_POWER_GAIN < 1.0f ) {
Chris@69:         return 0.0f;
Chris@69:     }
Chris@69:     return (silk_float)invGain;
Chris@69: }