ref: 1c6c3d17a7d1868ef49834405f5f0ee9f59a5a00
dir: /silk/float/silk_levinsondurbin_FLP.c/
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#include "silk_SigProc_FLP.h"
/* Solve the normal equations using the Levinson-Durbin recursion */
SKP_float silk_levinsondurbin_FLP( /* O prediction error energy */
SKP_float A[], /* O prediction coefficients [order] */
const SKP_float corr[], /* I input auto-correlations [order + 1] */
const opus_int order /* I prediction order */
)
{
opus_int i, mHalf, m;
SKP_float min_nrg, nrg, t, km, Atmp1, Atmp2;
min_nrg = 1e-12f * corr[ 0 ] + 1e-9f;
nrg = corr[ 0 ];
nrg = SKP_max_float(min_nrg, nrg);
A[ 0 ] = corr[ 1 ] / nrg;
nrg -= A[ 0 ] * corr[ 1 ];
nrg = SKP_max_float(min_nrg, nrg);
for( m = 1; m < order; m++ )
{
t = corr[ m + 1 ];
for( i = 0; i < m; i++ ) {
t -= A[ i ] * corr[ m - i ];
}
/* reflection coefficient */
km = t / nrg;
/* residual energy */
nrg -= km * t;
nrg = SKP_max_float(min_nrg, nrg);
mHalf = m >> 1;
for( i = 0; i < mHalf; i++ ) {
Atmp1 = A[ i ];
Atmp2 = A[ m - i - 1 ];
A[ m - i - 1 ] -= km * Atmp1;
A[ i ] -= km * Atmp2;
}
if( m & 1 ) {
A[ mHalf ] -= km * A[ mHalf ];
}
A[ m ] = km;
}
/* return the residual energy */
return nrg;
}