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ref: 55788c8c857f28f3b5e6d14cab978398d79fcf24
dir: /silk/fixed/find_LPC_FIX.c/

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

#include "main_FIX.h"
#include "tuning_parameters.h"

/* Finds LPC vector from correlations, and converts to NLSF */
void silk_find_LPC_FIX(
    opus_int16                       NLSF_Q15[],             /* O    NLSFs                                                           */
    opus_int8                        *interpIndex,           /* O    NLSF interpolation index, only used for NLSF interpolation      */
    const opus_int16                 prev_NLSFq_Q15[],       /* I    previous NLSFs, only used for NLSF interpolation                */
    const opus_int                   useInterpNLSFs,         /* I    Flag                                                            */
    const opus_int                   firstFrameAfterReset,   /* I    Flag                                                            */
    const opus_int                   LPC_order,              /* I    LPC order                                                       */
    const opus_int16                 x[],                    /* I    Input signal                                                    */
    const opus_int                   subfr_length,           /* I    Input signal subframe length including preceeding samples       */
    const opus_int                   nb_subfr                /* I:   Number of subframes                                             */
)
{
    opus_int     k;
    opus_int32   a_Q16[ MAX_LPC_ORDER ];
    opus_int     isInterpLower, shift;
    opus_int32   res_nrg0, res_nrg1;
    opus_int     rshift0, rshift1;

    /* Used only for LSF interpolation */
    opus_int32   a_tmp_Q16[ MAX_LPC_ORDER ], res_nrg_interp, res_nrg, res_tmp_nrg, res_nrg_2nd;
    opus_int     res_nrg_interp_Q, res_nrg_Q, res_tmp_nrg_Q, res_nrg_2nd_Q;
    opus_int16   a_tmp_Q12[ MAX_LPC_ORDER ];
    opus_int16   NLSF0_Q15[ MAX_LPC_ORDER ];
    opus_int16   LPC_res[ ( MAX_FRAME_LENGTH + MAX_NB_SUBFR * MAX_LPC_ORDER ) / 2 ];

    /* Default: no interpolation */
    *interpIndex = 4;

    /* Burg AR analysis for the full frame */
    silk_burg_modified( &res_nrg, &res_nrg_Q, a_Q16, x, subfr_length, nb_subfr, SILK_FIX_CONST( FIND_LPC_COND_FAC, 32 ), LPC_order );

    if( firstFrameAfterReset ) {
        silk_bwexpander_32( a_Q16, LPC_order, SILK_FIX_CONST( FIND_LPC_CHIRP_FIRST_FRAME, 16 ) );
    } else {
        silk_bwexpander_32( a_Q16, LPC_order, SILK_FIX_CONST( FIND_LPC_CHIRP, 16 ) );
    }

    if( useInterpNLSFs && !firstFrameAfterReset && nb_subfr == MAX_NB_SUBFR ) {

        /* Optimal solution for last 10 ms */
        silk_burg_modified( &res_tmp_nrg, &res_tmp_nrg_Q, a_tmp_Q16, x + ( MAX_NB_SUBFR >> 1 ) * subfr_length,
            subfr_length, ( MAX_NB_SUBFR >> 1 ), SILK_FIX_CONST( FIND_LPC_COND_FAC, 32 ), LPC_order );

        silk_bwexpander_32( a_tmp_Q16, LPC_order, SILK_FIX_CONST( FIND_LPC_CHIRP, 16 ) );

        /* subtract residual energy here, as that's easier than adding it to the    */
        /* residual energy of the first 10 ms in each iteration of the search below */
        shift = res_tmp_nrg_Q - res_nrg_Q;
        if( shift >= 0 ) {
            if( shift < 32 ) {
                res_nrg = res_nrg - silk_RSHIFT( res_tmp_nrg, shift );
            }
        } else {
            silk_assert( shift > -32 );
            res_nrg   = silk_RSHIFT( res_nrg, -shift ) - res_tmp_nrg;
            res_nrg_Q = res_tmp_nrg_Q;
        }

        /* Convert to NLSFs */
        silk_A2NLSF( NLSF_Q15, a_tmp_Q16, LPC_order );

        /* Search over interpolation indices to find the one with lowest residual energy */
        res_nrg_2nd = silk_int32_MAX;
        for( k = 3; k >= 0; k-- ) {
            /* Interpolate NLSFs for first half */
            silk_interpolate( NLSF0_Q15, prev_NLSFq_Q15, NLSF_Q15, k, LPC_order );

            /* Convert to LPC for residual energy evaluation */
            silk_NLSF2A( a_tmp_Q12, NLSF0_Q15, LPC_order );

            /* Calculate residual energy with NLSF interpolation */
            silk_LPC_analysis_filter( LPC_res, x, a_tmp_Q12, 2 * subfr_length, LPC_order );

            silk_sum_sqr_shift( &res_nrg0, &rshift0, LPC_res + LPC_order,                subfr_length - LPC_order );
            silk_sum_sqr_shift( &res_nrg1, &rshift1, LPC_res + LPC_order + subfr_length, subfr_length - LPC_order );

            /* Add subframe energies from first half frame */
            shift = rshift0 - rshift1;
            if( shift >= 0 ) {
                res_nrg1         = silk_RSHIFT( res_nrg1, shift );
                res_nrg_interp_Q = -rshift0;
            } else {
                res_nrg0         = silk_RSHIFT( res_nrg0, -shift );
                res_nrg_interp_Q = -rshift1;
            }
            res_nrg_interp = silk_ADD32( res_nrg0, res_nrg1 );

            /* Compare with first half energy without NLSF interpolation, or best interpolated value so far */
            shift = res_nrg_interp_Q - res_nrg_Q;
            if( shift >= 0 ) {
                if( silk_RSHIFT( res_nrg_interp, shift ) < res_nrg ) {
                    isInterpLower = silk_TRUE;
                } else {
                    isInterpLower = silk_FALSE;
                }
            } else {
                if( -shift < 32 ) {
                    if( res_nrg_interp < silk_RSHIFT( res_nrg, -shift ) ) {
                        isInterpLower = silk_TRUE;
                    } else {
                        isInterpLower = silk_FALSE;
                    }
                } else {
                    isInterpLower = silk_FALSE;
                }
            }

            /* Determine whether current interpolated NLSFs are best so far */
            if( isInterpLower == silk_TRUE ) {
                /* Interpolation has lower residual energy */
                res_nrg   = res_nrg_interp;
                res_nrg_Q = res_nrg_interp_Q;
                *interpIndex = (opus_int8)k;
            }
            res_nrg_2nd   = res_nrg_interp;
            res_nrg_2nd_Q = res_nrg_interp_Q;
        }
    }

    if( *interpIndex == 4 ) {
        /* NLSF interpolation is currently inactive, calculate NLSFs from full frame AR coefficients */
        silk_A2NLSF( NLSF_Q15, a_Q16, LPC_order );
    }

    silk_assert( *interpIndex == 4 || ( useInterpNLSFs && !firstFrameAfterReset && nb_subfr == MAX_NB_SUBFR ) );
}