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1 /***********************************************************************
2 Copyright (c) 2006-2011, Skype Limited. All rights reserved.
3 Redistribution and use in source and binary forms, with or without
4 modification, are permitted provided that the following conditions
5 are met:
6 - Redistributions of source code must retain the above copyright notice,
7 this list of conditions and the following disclaimer.
8 - Redistributions in binary form must reproduce the above copyright
9 notice, this list of conditions and the following disclaimer in the
10 documentation and/or other materials provided with the distribution.
11 - Neither the name of Internet Society, IETF or IETF Trust, nor the
12 names of specific contributors, may be used to endorse or promote
13 products derived from this software without specific prior written
14 permission.
15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
16 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
19 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
20 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
21 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
22 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
23 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
24 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
25 POSSIBILITY OF SUCH DAMAGE.
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 
35 #define RC_THRESHOLD        0.9999f
36 
37 /* compute inverse of LPC prediction gain, and                          */
38 /* test if LPC coefficients are stable (all poles within unit circle)   */
39 /* this code is based on silk_a2k_FLP()                                 */
silk_LPC_inverse_pred_gain_FLP(const silk_float * A,opus_int32 order)40 silk_float silk_LPC_inverse_pred_gain_FLP(  /* O    return inverse prediction gain, energy domain               */
41     const silk_float    *A,                 /* I    prediction coefficients [order]                             */
42     opus_int32          order               /* I    prediction order                                            */
43 )
44 {
45     opus_int   k, n;
46     double     invGain, rc, rc_mult1, rc_mult2;
47     silk_float Atmp[ 2 ][ SILK_MAX_ORDER_LPC ];
48     silk_float *Aold, *Anew;
49 
50     Anew = Atmp[ order & 1 ];
51     silk_memcpy( Anew, A, order * sizeof(silk_float) );
52 
53     invGain = 1.0;
54     for( k = order - 1; k > 0; k-- ) {
55         rc = -Anew[ k ];
56         if( rc > RC_THRESHOLD || rc < -RC_THRESHOLD ) {
57             return 0.0f;
58         }
59         rc_mult1 = 1.0f - rc * rc;
60         rc_mult2 = 1.0f / rc_mult1;
61         invGain *= rc_mult1;
62         /* swap pointers */
63         Aold = Anew;
64         Anew = Atmp[ k & 1 ];
65         for( n = 0; n < k; n++ ) {
66             Anew[ n ] = (silk_float)( ( Aold[ n ] - Aold[ k - n - 1 ] * rc ) * rc_mult2 );
67         }
68     }
69     rc = -Anew[ 0 ];
70     if( rc > RC_THRESHOLD || rc < -RC_THRESHOLD ) {
71         return 0.0f;
72     }
73     rc_mult1 = 1.0f - rc * rc;
74     invGain *= rc_mult1;
75     return (silk_float)invGain;
76 }
77