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26***********************************************************************/
27
28#ifdef HAVE_CONFIG_H
29#include "config.h"
30#endif
31
32#include "SigProc_FLP.h"
33
34silk_float silk_schur_FLP(                  /* O    returns residual energy                                     */
35    silk_float          refl_coef[],        /* O    reflection coefficients (length order)                      */
36    const silk_float    auto_corr[],        /* I    autocorrelation sequence (length order+1)                   */
37    opus_int            order               /* I    order                                                       */
38)
39{
40    opus_int   k, n;
41    silk_float C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
42    silk_float Ctmp1, Ctmp2, rc_tmp;
43
44    silk_assert( order==6||order==8||order==10||order==12||order==14||order==16 );
45
46    /* Copy correlations */
47    for( k = 0; k < order+1; k++ ) {
48        C[ k ][ 0 ] = C[ k ][ 1 ] = auto_corr[ k ];
49    }
50
51    for( k = 0; k < order; k++ ) {
52        /* Get reflection coefficient */
53        rc_tmp = -C[ k + 1 ][ 0 ] / silk_max_float( C[ 0 ][ 1 ], 1e-9f );
54
55        /* Save the output */
56        refl_coef[ k ] = rc_tmp;
57
58        /* Update correlations */
59        for( n = 0; n < order - k; n++ ) {
60            Ctmp1 = C[ n + k + 1 ][ 0 ];
61            Ctmp2 = C[ n ][ 1 ];
62            C[ n + k + 1 ][ 0 ] = Ctmp1 + Ctmp2 * rc_tmp;
63            C[ n ][ 1 ]         = Ctmp2 + Ctmp1 * rc_tmp;
64        }
65    }
66
67    /* Return residual energy */
68    return C[ 0 ][ 1 ];
69}
70
71