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27
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31
32 /* NLSF stabilizer: */
33 /* */
34 /* - Moves NLSFs further apart if they are too close */
35 /* - Moves NLSFs away from borders if they are too close */
36 /* - High effort to achieve a modification with minimum */
37 /* Euclidean distance to input vector */
38 /* - Output are sorted NLSF coefficients */
39 /* */
40
41 #include "SigProc_FIX.h"
42
43 /* Constant Definitions */
44 #define MAX_LOOPS 20
45
46 /* NLSF stabilizer, for a single input data vector */
silk_NLSF_stabilize(opus_int16 * NLSF_Q15,const opus_int16 * NDeltaMin_Q15,const opus_int L)47 void silk_NLSF_stabilize(
48 opus_int16 *NLSF_Q15, /* I/O Unstable/stabilized normalized LSF vector in Q15 [L] */
49 const opus_int16 *NDeltaMin_Q15, /* I Min distance vector, NDeltaMin_Q15[L] must be >= 1 [L+1] */
50 const opus_int L /* I Number of NLSF parameters in the input vector */
51 )
52 {
53 opus_int i, I=0, k, loops;
54 opus_int16 center_freq_Q15;
55 opus_int32 diff_Q15, min_diff_Q15, min_center_Q15, max_center_Q15;
56
57 /* This is necessary to ensure an output within range of a opus_int16 */
58 silk_assert( NDeltaMin_Q15[L] >= 1 );
59
60 for( loops = 0; loops < MAX_LOOPS; loops++ ) {
61 /**************************/
62 /* Find smallest distance */
63 /**************************/
64 /* First element */
65 min_diff_Q15 = NLSF_Q15[0] - NDeltaMin_Q15[0];
66 I = 0;
67 /* Middle elements */
68 for( i = 1; i <= L-1; i++ ) {
69 diff_Q15 = NLSF_Q15[i] - ( NLSF_Q15[i-1] + NDeltaMin_Q15[i] );
70 if( diff_Q15 < min_diff_Q15 ) {
71 min_diff_Q15 = diff_Q15;
72 I = i;
73 }
74 }
75 /* Last element */
76 diff_Q15 = ( 1 << 15 ) - ( NLSF_Q15[L-1] + NDeltaMin_Q15[L] );
77 if( diff_Q15 < min_diff_Q15 ) {
78 min_diff_Q15 = diff_Q15;
79 I = L;
80 }
81
82 /***************************************************/
83 /* Now check if the smallest distance non-negative */
84 /***************************************************/
85 if( min_diff_Q15 >= 0 ) {
86 return;
87 }
88
89 if( I == 0 ) {
90 /* Move away from lower limit */
91 NLSF_Q15[0] = NDeltaMin_Q15[0];
92
93 } else if( I == L) {
94 /* Move away from higher limit */
95 NLSF_Q15[L-1] = ( 1 << 15 ) - NDeltaMin_Q15[L];
96
97 } else {
98 /* Find the lower extreme for the location of the current center frequency */
99 min_center_Q15 = 0;
100 for( k = 0; k < I; k++ ) {
101 min_center_Q15 += NDeltaMin_Q15[k];
102 }
103 min_center_Q15 += silk_RSHIFT( NDeltaMin_Q15[I], 1 );
104
105 /* Find the upper extreme for the location of the current center frequency */
106 max_center_Q15 = 1 << 15;
107 for( k = L; k > I; k-- ) {
108 max_center_Q15 -= NDeltaMin_Q15[k];
109 }
110 max_center_Q15 -= silk_RSHIFT( NDeltaMin_Q15[I], 1 );
111
112 /* Move apart, sorted by value, keeping the same center frequency */
113 center_freq_Q15 = (opus_int16)silk_LIMIT_32( silk_RSHIFT_ROUND( (opus_int32)NLSF_Q15[I-1] + (opus_int32)NLSF_Q15[I], 1 ),
114 min_center_Q15, max_center_Q15 );
115 NLSF_Q15[I-1] = center_freq_Q15 - silk_RSHIFT( NDeltaMin_Q15[I], 1 );
116 NLSF_Q15[I] = NLSF_Q15[I-1] + NDeltaMin_Q15[I];
117 }
118 }
119
120 /* Safe and simple fall back method, which is less ideal than the above */
121 if( loops == MAX_LOOPS )
122 {
123 /* Insertion sort (fast for already almost sorted arrays): */
124 /* Best case: O(n) for an already sorted array */
125 /* Worst case: O(n^2) for an inversely sorted array */
126 silk_insertion_sort_increasing_all_values_int16( &NLSF_Q15[0], L );
127
128 /* First NLSF should be no less than NDeltaMin[0] */
129 NLSF_Q15[0] = silk_max_int( NLSF_Q15[0], NDeltaMin_Q15[0] );
130
131 /* Keep delta_min distance between the NLSFs */
132 for( i = 1; i < L; i++ )
133 NLSF_Q15[i] = silk_max_int( NLSF_Q15[i], NLSF_Q15[i-1] + NDeltaMin_Q15[i] );
134
135 /* Last NLSF should be no higher than 1 - NDeltaMin[L] */
136 NLSF_Q15[L-1] = silk_min_int( NLSF_Q15[L-1], (1<<15) - NDeltaMin_Q15[L] );
137
138 /* Keep NDeltaMin distance between the NLSFs */
139 for( i = L-2; i >= 0; i-- )
140 NLSF_Q15[i] = silk_min_int( NLSF_Q15[i], NLSF_Q15[i+1] - NDeltaMin_Q15[i+1] );
141 }
142 }
143