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27
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31
32 #include "SigProc_FLP.h"
33
34 /* Solve the normal equations using the Levinson-Durbin recursion */
silk_levinsondurbin_FLP(silk_float A[],const silk_float corr[],const opus_int order)35 silk_float silk_levinsondurbin_FLP( /* O prediction error energy */
36 silk_float A[], /* O prediction coefficients [order] */
37 const silk_float corr[], /* I input auto-correlations [order + 1] */
38 const opus_int order /* I prediction order */
39 )
40 {
41 opus_int i, mHalf, m;
42 silk_float min_nrg, nrg, t, km, Atmp1, Atmp2;
43
44 min_nrg = 1e-12f * corr[ 0 ] + 1e-9f;
45 nrg = corr[ 0 ];
46 nrg = silk_max_float(min_nrg, nrg);
47 A[ 0 ] = corr[ 1 ] / nrg;
48 nrg -= A[ 0 ] * corr[ 1 ];
49 nrg = silk_max_float(min_nrg, nrg);
50
51 for( m = 1; m < order; m++ )
52 {
53 t = corr[ m + 1 ];
54 for( i = 0; i < m; i++ ) {
55 t -= A[ i ] * corr[ m - i ];
56 }
57
58 /* reflection coefficient */
59 km = t / nrg;
60
61 /* residual energy */
62 nrg -= km * t;
63 nrg = silk_max_float(min_nrg, nrg);
64
65 mHalf = m >> 1;
66 for( i = 0; i < mHalf; i++ ) {
67 Atmp1 = A[ i ];
68 Atmp2 = A[ m - i - 1 ];
69 A[ m - i - 1 ] -= km * Atmp1;
70 A[ i ] -= km * Atmp2;
71 }
72 if( m & 1 ) {
73 A[ mHalf ] -= km * A[ mHalf ];
74 }
75 A[ m ] = km;
76 }
77
78 /* return the residual energy */
79 return nrg;
80 }
81
82