ref: 4154dad41e1fe1cd86812836c73787ed5be962dd
dir: /silk/fixed/silk_find_LPC_FIX.c/
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#include "silk_main_FIX.h"
#include "silk_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 - SKP_RSHIFT( res_tmp_nrg, shift );
}
} else {
SKP_assert( shift > -32 );
res_nrg = SKP_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 = SKP_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 = SKP_RSHIFT( res_nrg1, shift );
res_nrg_interp_Q = -rshift0;
} else {
res_nrg0 = SKP_RSHIFT( res_nrg0, -shift );
res_nrg_interp_Q = -rshift1;
}
res_nrg_interp = SKP_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( SKP_RSHIFT( res_nrg_interp, shift ) < res_nrg ) {
isInterpLower = SKP_TRUE;
} else {
isInterpLower = SKP_FALSE;
}
} else {
if( -shift < 32 ) {
if( res_nrg_interp < SKP_RSHIFT( res_nrg, -shift ) ) {
isInterpLower = SKP_TRUE;
} else {
isInterpLower = SKP_FALSE;
}
} else {
isInterpLower = SKP_FALSE;
}
}
/* Determine whether current interpolated NLSFs are best so far */
if( isInterpLower == SKP_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 );
}
SKP_assert( *interpIndex == 4 || ( useInterpNLSFs && !firstFrameAfterReset && nb_subfr == MAX_NB_SUBFR ) );
}