opus/silk/float/schur_FLP.c

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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "SigProc_FLP.h"

silk_float silk_schur_FLP(                  /* O    returns residual energy                                     */
    silk_float          refl_coef[],        /* O    reflection coefficients (length order)                      */
    const silk_float    auto_corr[],        /* I    autocorrelation sequence (length order+1)                   */
    opus_int            order               /* I    order                                                       */
)
{
    opus_int   k, n;
    double C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
    double Ctmp1, Ctmp2, rc_tmp;

    silk_assert( order <= SILK_MAX_ORDER_LPC );

    /* Copy correlations */
    for( k = 0; k < order+1; k++ ) {
        C[ k ][ 0 ] = C[ k ][ 1 ] = auto_corr[ k ];
    }

    for( k = 0; k < order; k++ ) {
        /* Get reflection coefficient */
        rc_tmp = -C[ k + 1 ][ 0 ] / silk_max_float( C[ 0 ][ 1 ], 1e-9f );

        /* Save the output */
        refl_coef[ k ] = (silk_float)rc_tmp;

        /* Update correlations */
        for( n = 0; n < order - k; n++ ) {
            Ctmp1 = C[ n + k + 1 ][ 0 ];
            Ctmp2 = C[ n ][ 1 ];
            C[ n + k + 1 ][ 0 ] = Ctmp1 + Ctmp2 * rc_tmp;
            C[ n ][ 1 ]         = Ctmp2 + Ctmp1 * rc_tmp;
        }
    }

    /* Return residual energy */
    return (silk_float)C[ 0 ][ 1 ];
}