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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