ref: fe741259c1050baa5c828444dd5a968ed658d1fb
dir: /silk/float/SKP_Silk_find_LPC_FLP.c/
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#include "SKP_Silk_main_FLP.h"
#include "SKP_Silk_tuning_parameters.h"
void SKP_Silk_find_LPC_FLP(
SKP_int16 NLSF_Q15[], /* O NLSFs */
SKP_int8 *interpIndex, /* O NLSF interp. index for NLSF interp. */
const SKP_int16 prev_NLSFq_Q15[], /* I Previous NLSFs, for NLSF interpolation */
const SKP_int useInterpNLSFs, /* I Flag */
const SKP_int firstFrameAfterReset, /* I Flag */
const SKP_int LPC_order, /* I LPC order */
const SKP_float x[], /* I Input signal */
const SKP_int subfr_length, /* I Subframe length incl preceeding samples */
const SKP_int nb_subfr /* I: Number of subframes */
)
{
SKP_int k;
SKP_float a[ MAX_LPC_ORDER ];
/* Used only for NLSF interpolation */
double res_nrg, res_nrg_2nd, res_nrg_interp;
SKP_int16 NLSF0_Q15[ MAX_LPC_ORDER ];
SKP_float a_tmp[ MAX_LPC_ORDER ];
SKP_float LPC_res[ ( MAX_FRAME_LENGTH + MAX_NB_SUBFR * MAX_LPC_ORDER ) / 2 ];
/* Default: No interpolation */
*interpIndex = 4;
/* Burg AR analysis for the full frame */
res_nrg = SKP_Silk_burg_modified_FLP( a, x, subfr_length, nb_subfr, FIND_LPC_COND_FAC, LPC_order );
if( firstFrameAfterReset ) {
SKP_Silk_bwexpander_FLP( a, LPC_order, FIND_LPC_CHIRP_FIRST_FRAME );
} else {
SKP_Silk_bwexpander_FLP( a_tmp, LPC_order, FIND_LPC_CHIRP );
}
if( useInterpNLSFs && !firstFrameAfterReset && nb_subfr == MAX_NB_SUBFR ) {
/* Optimal solution for last 10 ms; 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 */
res_nrg -= SKP_Silk_burg_modified_FLP( a_tmp, x + ( MAX_NB_SUBFR / 2 ) * subfr_length,
subfr_length, MAX_NB_SUBFR / 2, FIND_LPC_COND_FAC, LPC_order );
SKP_Silk_bwexpander_FLP( a_tmp, LPC_order, FIND_LPC_CHIRP );
/* Convert to NLSFs */
SKP_Silk_A2NLSF_FLP( NLSF_Q15, a_tmp, LPC_order );
/* Search over interpolation indices to find the one with lowest residual energy */
res_nrg_2nd = SKP_float_MAX;
for( k = 3; k >= 0; k-- ) {
/* Interpolate NLSFs for first half */
SKP_Silk_interpolate( NLSF0_Q15, prev_NLSFq_Q15, NLSF_Q15, k, LPC_order );
/* Convert to LPC for residual energy evaluation */
SKP_Silk_NLSF2A_stable_FLP( a_tmp, NLSF0_Q15, LPC_order );
/* Calculate residual energy with LSF interpolation */
SKP_Silk_LPC_analysis_filter_FLP( LPC_res, a_tmp, x, 2 * subfr_length, LPC_order );
res_nrg_interp =
SKP_Silk_energy_FLP( LPC_res + LPC_order, subfr_length - LPC_order ) +
SKP_Silk_energy_FLP( LPC_res + LPC_order + subfr_length, subfr_length - LPC_order );
/* Determine whether current interpolated NLSFs are best so far */
if( res_nrg_interp < res_nrg ) {
/* Interpolation has lower residual energy */
res_nrg = res_nrg_interp;
*interpIndex = (SKP_int8)k;
} else if( res_nrg_interp > res_nrg_2nd ) {
/* No reason to continue iterating - residual energies will continue to climb */
break;
}
res_nrg_2nd = res_nrg_interp;
}
}
if( *interpIndex == 4 ) {
/* NLSF interpolation is currently inactive, calculate NLSFs from full frame AR coefficients */
SKP_Silk_A2NLSF_FLP( NLSF_Q15, a, LPC_order );
}
SKP_assert( *interpIndex == 4 || ( useInterpNLSFs && !firstFrameAfterReset && nb_subfr == MAX_NB_SUBFR ) );
}