ref: c43b1bc8c0a55dde4b7b33cf3f6eba9595ecdd99
dir: /silk/NLSF_stabilize.c/
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
/* NLSF stabilizer: */
/* */
/* - Moves NLSFs further apart if they are too close */
/* - Moves NLSFs away from borders if they are too close */
/* - High effort to achieve a modification with minimum */
/* Euclidean distance to input vector */
/* - Output are sorted NLSF coefficients */
/* */
#include "SigProc_FIX.h"
/* Constant Definitions */
#define MAX_LOOPS 20
/* NLSF stabilizer, for a single input data vector */
void silk_NLSF_stabilize(
opus_int16 *NLSF_Q15, /* I/O Unstable/stabilized normalized LSF vector in Q15 [L] */
const opus_int16 *NDeltaMin_Q15, /* I Min distance vector, NDeltaMin_Q15[L] must be >= 1 [L+1] */
const opus_int L /* I Number of NLSF parameters in the input vector */
)
{
opus_int i, I=0, k, loops;
opus_int16 center_freq_Q15;
opus_int32 diff_Q15, min_diff_Q15, min_center_Q15, max_center_Q15;
/* This is necessary to ensure an output within range of a opus_int16 */
silk_assert( NDeltaMin_Q15[L] >= 1 );
for( loops = 0; loops < MAX_LOOPS; loops++ ) {
/**************************/
/* Find smallest distance */
/**************************/
/* First element */
min_diff_Q15 = NLSF_Q15[0] - NDeltaMin_Q15[0];
I = 0;
/* Middle elements */
for( i = 1; i <= L-1; i++ ) {
diff_Q15 = NLSF_Q15[i] - ( NLSF_Q15[i-1] + NDeltaMin_Q15[i] );
if( diff_Q15 < min_diff_Q15 ) {
min_diff_Q15 = diff_Q15;
I = i;
}
}
/* Last element */
diff_Q15 = ( 1 << 15 ) - ( NLSF_Q15[L-1] + NDeltaMin_Q15[L] );
if( diff_Q15 < min_diff_Q15 ) {
min_diff_Q15 = diff_Q15;
I = L;
}
/***************************************************/
/* Now check if the smallest distance non-negative */
/***************************************************/
if( min_diff_Q15 >= 0 ) {
return;
}
if( I == 0 ) {
/* Move away from lower limit */
NLSF_Q15[0] = NDeltaMin_Q15[0];
} else if( I == L) {
/* Move away from higher limit */
NLSF_Q15[L-1] = ( 1 << 15 ) - NDeltaMin_Q15[L];
} else {
/* Find the lower extreme for the location of the current center frequency */
min_center_Q15 = 0;
for( k = 0; k < I; k++ ) {
min_center_Q15 += NDeltaMin_Q15[k];
}
min_center_Q15 += silk_RSHIFT( NDeltaMin_Q15[I], 1 );
/* Find the upper extreme for the location of the current center frequency */
max_center_Q15 = 1 << 15;
for( k = L; k > I; k-- ) {
max_center_Q15 -= NDeltaMin_Q15[k];
}
max_center_Q15 -= silk_RSHIFT( NDeltaMin_Q15[I], 1 );
/* Move apart, sorted by value, keeping the same center frequency */
center_freq_Q15 = (opus_int16)silk_LIMIT_32( silk_RSHIFT_ROUND( (opus_int32)NLSF_Q15[I-1] + (opus_int32)NLSF_Q15[I], 1 ),
min_center_Q15, max_center_Q15 );
NLSF_Q15[I-1] = center_freq_Q15 - silk_RSHIFT( NDeltaMin_Q15[I], 1 );
NLSF_Q15[I] = NLSF_Q15[I-1] + NDeltaMin_Q15[I];
}
}
/* Safe and simple fall back method, which is less ideal than the above */
if( loops == MAX_LOOPS )
{
/* Insertion sort (fast for already almost sorted arrays): */
/* Best case: O(n) for an already sorted array */
/* Worst case: O(n^2) for an inversely sorted array */
silk_insertion_sort_increasing_all_values_int16( &NLSF_Q15[0], L );
/* First NLSF should be no less than NDeltaMin[0] */
NLSF_Q15[0] = silk_max_int( NLSF_Q15[0], NDeltaMin_Q15[0] );
/* Keep delta_min distance between the NLSFs */
for( i = 1; i < L; i++ )
NLSF_Q15[i] = silk_max_int( NLSF_Q15[i], NLSF_Q15[i-1] + NDeltaMin_Q15[i] );
/* Last NLSF should be no higher than 1 - NDeltaMin[L] */
NLSF_Q15[L-1] = silk_min_int( NLSF_Q15[L-1], (1<<15) - NDeltaMin_Q15[L] );
/* Keep NDeltaMin distance between the NLSFs */
for( i = L-2; i >= 0; i-- )
NLSF_Q15[i] = silk_min_int( NLSF_Q15[i], NLSF_Q15[i+1] - NDeltaMin_Q15[i+1] );
}
}