michael@0: /***********************************************************************
michael@0: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
michael@0: Redistribution and use in source and binary forms, with or without
michael@0: modification, are permitted provided that the following conditions
michael@0: are met:
michael@0: - Redistributions of source code must retain the above copyright notice,
michael@0: this list of conditions and the following disclaimer.
michael@0: - Redistributions in binary form must reproduce the above copyright
michael@0: notice, this list of conditions and the following disclaimer in the
michael@0: documentation and/or other materials provided with the distribution.
michael@0: - Neither the name of Internet Society, IETF or IETF Trust, nor the
michael@0: names of specific contributors, may be used to endorse or promote
michael@0: products derived from this software without specific prior written
michael@0: permission.
michael@0: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
michael@0: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
michael@0: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
michael@0: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
michael@0: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
michael@0: CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
michael@0: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
michael@0: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
michael@0: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
michael@0: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
michael@0: POSSIBILITY OF SUCH DAMAGE.
michael@0: ***********************************************************************/
michael@0: 
michael@0: #ifdef HAVE_CONFIG_H
michael@0: #include "config.h"
michael@0: #endif
michael@0: 
michael@0: #include "SigProc_FIX.h"
michael@0: #include "SigProc_FLP.h"
michael@0: 
michael@0: #define RC_THRESHOLD        0.9999f
michael@0: 
michael@0: /* compute inverse of LPC prediction gain, and                          */
michael@0: /* test if LPC coefficients are stable (all poles within unit circle)   */
michael@0: /* this code is based on silk_a2k_FLP()                                 */
michael@0: silk_float silk_LPC_inverse_pred_gain_FLP(  /* O    return inverse prediction gain, energy domain               */
michael@0:     const silk_float    *A,                 /* I    prediction coefficients [order]                             */
michael@0:     opus_int32          order               /* I    prediction order                                            */
michael@0: )
michael@0: {
michael@0:     opus_int   k, n;
michael@0:     double     invGain, rc, rc_mult1, rc_mult2;
michael@0:     silk_float Atmp[ 2 ][ SILK_MAX_ORDER_LPC ];
michael@0:     silk_float *Aold, *Anew;
michael@0: 
michael@0:     Anew = Atmp[ order & 1 ];
michael@0:     silk_memcpy( Anew, A, order * sizeof(silk_float) );
michael@0: 
michael@0:     invGain = 1.0;
michael@0:     for( k = order - 1; k > 0; k-- ) {
michael@0:         rc = -Anew[ k ];
michael@0:         if( rc > RC_THRESHOLD || rc < -RC_THRESHOLD ) {
michael@0:             return 0.0f;
michael@0:         }
michael@0:         rc_mult1 = 1.0f - rc * rc;
michael@0:         rc_mult2 = 1.0f / rc_mult1;
michael@0:         invGain *= rc_mult1;
michael@0:         /* swap pointers */
michael@0:         Aold = Anew;
michael@0:         Anew = Atmp[ k & 1 ];
michael@0:         for( n = 0; n < k; n++ ) {
michael@0:             Anew[ n ] = (silk_float)( ( Aold[ n ] - Aold[ k - n - 1 ] * rc ) * rc_mult2 );
michael@0:         }
michael@0:     }
michael@0:     rc = -Anew[ 0 ];
michael@0:     if( rc > RC_THRESHOLD || rc < -RC_THRESHOLD ) {
michael@0:         return 0.0f;
michael@0:     }
michael@0:     rc_mult1 = 1.0f - rc * rc;
michael@0:     invGain *= rc_mult1;
michael@0:     return (silk_float)invGain;
michael@0: }