cannam@154: /***********************************************************************
cannam@154: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
cannam@154: Redistribution and use in source and binary forms, with or without
cannam@154: modification, are permitted provided that the following conditions
cannam@154: are met:
cannam@154: - Redistributions of source code must retain the above copyright notice,
cannam@154: this list of conditions and the following disclaimer.
cannam@154: - Redistributions in binary form must reproduce the above copyright
cannam@154: notice, this list of conditions and the following disclaimer in the
cannam@154: documentation and/or other materials provided with the distribution.
cannam@154: - Neither the name of Internet Society, IETF or IETF Trust, nor the
cannam@154: names of specific contributors, may be used to endorse or promote
cannam@154: products derived from this software without specific prior written
cannam@154: permission.
cannam@154: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
cannam@154: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
cannam@154: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
cannam@154: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
cannam@154: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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cannam@154: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
cannam@154: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
cannam@154: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
cannam@154: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
cannam@154: POSSIBILITY OF SUCH DAMAGE.
cannam@154: ***********************************************************************/
cannam@154: 
cannam@154: #ifdef HAVE_CONFIG_H
cannam@154: #include "config.h"
cannam@154: #endif
cannam@154: 
cannam@154: #include "SigProc_FIX.h"
cannam@154: #include "SigProc_FLP.h"
cannam@154: #include "define.h"
cannam@154: 
cannam@154: /* compute inverse of LPC prediction gain, and                          */
cannam@154: /* test if LPC coefficients are stable (all poles within unit circle)   */
cannam@154: /* this code is based on silk_a2k_FLP()                                 */
cannam@154: silk_float silk_LPC_inverse_pred_gain_FLP(  /* O    return inverse prediction gain, energy domain               */
cannam@154:     const silk_float    *A,                 /* I    prediction coefficients [order]                             */
cannam@154:     opus_int32          order               /* I    prediction order                                            */
cannam@154: )
cannam@154: {
cannam@154:     opus_int   k, n;
cannam@154:     double     invGain, rc, rc_mult1, rc_mult2, tmp1, tmp2;
cannam@154:     silk_float Atmp[ SILK_MAX_ORDER_LPC ];
cannam@154: 
cannam@154:     silk_memcpy( Atmp, A, order * sizeof(silk_float) );
cannam@154: 
cannam@154:     invGain = 1.0;
cannam@154:     for( k = order - 1; k > 0; k-- ) {
cannam@154:         rc = -Atmp[ k ];
cannam@154:         rc_mult1 = 1.0f - rc * rc;
cannam@154:         invGain *= rc_mult1;
cannam@154:         if( invGain * MAX_PREDICTION_POWER_GAIN < 1.0f ) {
cannam@154:             return 0.0f;
cannam@154:         }
cannam@154:         rc_mult2 = 1.0f / rc_mult1;
cannam@154:         for( n = 0; n < (k + 1) >> 1; n++ ) {
cannam@154:             tmp1 = Atmp[ n ];
cannam@154:             tmp2 = Atmp[ k - n - 1 ];
cannam@154:             Atmp[ n ]         = (silk_float)( ( tmp1 - tmp2 * rc ) * rc_mult2 );
cannam@154:             Atmp[ k - n - 1 ] = (silk_float)( ( tmp2 - tmp1 * rc ) * rc_mult2 );
cannam@154:         }
cannam@154:     }
cannam@154:     rc = -Atmp[ 0 ];
cannam@154:     rc_mult1 = 1.0f - rc * rc;
cannam@154:     invGain *= rc_mult1;
cannam@154:     if( invGain * MAX_PREDICTION_POWER_GAIN < 1.0f ) {
cannam@154:         return 0.0f;
cannam@154:     }
cannam@154:     return (silk_float)invGain;
cannam@154: }