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- /***********************************************************************
- Copyright (c) 2006-2011, Skype Limited. All rights reserved.
- Redistribution and use in source and binary forms, with or without
- modification, are permitted provided that the following conditions
- are met:
- - Redistributions of source code must retain the above copyright notice,
- this list of conditions and the following disclaimer.
- - Redistributions in binary form must reproduce the above copyright
- notice, this list of conditions and the following disclaimer in the
- documentation and/or other materials provided with the distribution.
- - Neither the name of Internet Society, IETF or IETF Trust, nor the
- names of specific contributors, may be used to endorse or promote
- products derived from this software without specific prior written
- permission.
- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
- CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
- INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
- CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
- POSSIBILITY OF SUCH DAMAGE.
- ***********************************************************************/
- #ifdef HAVE_CONFIG_H
- #include "config.h"
- #endif
- #include "SigProc_FLP.h"
- #include "tuning_parameters.h"
- #include "define.h"
- /* This code implements the method from https://www.opus-codec.org/docs/vos_fastburg.pdf */
- /* Compute reflection coefficients from input signal */
- silk_float silk_burg_modified_FLP(
- silk_float af[], /* O prediction coefficients (length order) */
- const silk_float x[], /* I input signal, length: nb_subfr*(D+L_sub) */
- const silk_float minInvGain, /* I minimum inverse prediction gain */
- const opus_int subfr_length, /* I input signal subframe length (incl. D preceding samples) */
- const opus_int nb_subfr, /* I number of subframes stacked in x */
- const opus_int D /* I order */
- )
- {
- opus_int k, n, s, reached_max_gain;
- double invGain, num, nrg, rc, tmp1, tmp2, x1, x2, atmp;
- const silk_float *x_ptr;
- double c[ SILK_MAX_ORDER_LPC + 1 ];
- double g[ SILK_MAX_ORDER_LPC + 1 ];
- double a[ SILK_MAX_ORDER_LPC ];
- /* Compute autocorrelations, added over subframes */
- silk_memset( c, 0, (D + 1) * sizeof( double ) );
- for( s = 0; s < nb_subfr; s++ ) {
- x_ptr = x + s * subfr_length;
- for( n = 0; n < D + 1; n++ ) {
- c[ n ] += silk_inner_product_FLP( x_ptr, x_ptr + n, subfr_length - n );
- }
- }
- for( n = 0; n < D + 1; n++ ) {
- c[ n ] *= 2.0;
- }
- /* Initialize */
- c[ 0 ] += FIND_LPC_COND_FAC * c[ 0 ] + 1e-9f ;
- g[ 0 ] = c[ 0 ];
- tmp1 = 0.0f;
- for( s = 0; s < nb_subfr; s++ ) {
- x_ptr = x + s * subfr_length;
- x1 = x_ptr[ 0 ];
- x2 = x_ptr[ subfr_length - 1 ];
- tmp1 += x1 * x1 + x2 * x2;
- }
- g[ 0 ] -= tmp1;
- g[ 1 ] = c[ 1 ];
- rc = - g[ 1 ] / g[ 0 ];
- silk_assert( rc > -1.0 && rc < 1.0 );
- a[ 0 ] = rc;
- invGain = ( 1.0 - rc * rc );
- reached_max_gain = 0;
- for( n = 1; n < D; n++ ) {
- for( k = 0; k < (n >> 1) + 1; k++ ) {
- tmp1 = g[ k ];
- tmp2 = g[ n - k ];
- g[ k ] = tmp1 + rc * tmp2;
- g[ n - k ] = tmp2 + rc * tmp1;
- }
- for( s = 0; s < nb_subfr; s++ ) {
- x_ptr = x + s * subfr_length;
- x1 = x_ptr[ n ];
- x2 = x_ptr[ subfr_length - n - 1 ];
- tmp1 = x1;
- tmp2 = x2;
- for( k = 0; k < n; k++ ) {
- atmp = a[ k ];
- c[ k + 1 ] -= x1 * x_ptr[ n - k - 1 ] + x2 * x_ptr[ subfr_length - n + k ];
- tmp1 += x_ptr[ n - k - 1 ] * atmp;
- tmp2 += x_ptr[ subfr_length - n + k ] * atmp;
- }
- for( k = 0; k <= n; k++ ) {
- g[ k ] -= tmp1 * x_ptr[ n - k ] + tmp2 * x_ptr[ subfr_length - n + k - 1 ];
- }
- }
- /* Calculate nominator and denominator for the next order reflection (parcor) coefficient */
- tmp1 = c[ n + 1 ];
- num = 0.0f;
- nrg = g[ 0 ];
- for( k = 0; k < n; k++ ) {
- atmp = a[ k ];
- tmp1 += c[ n - k ] * atmp;
- num += g[ n - k ] * atmp;
- nrg += g[ k + 1 ] * atmp;
- }
- g[ n + 1] = tmp1;
- num += tmp1;
- silk_assert( nrg > 0.0 );
- /* Calculate the next order reflection (parcor) coefficient */
- rc = -num / nrg;
- silk_assert( rc > -1.0 && rc < 1.0 );
- /* Update inverse prediction gain */
- tmp1 = invGain * ( 1.0 - rc * rc );
- if( tmp1 <= minInvGain ) {
- /* Max prediction gain exceeded; set reflection coefficient such that max prediction gain is exactly hit */
- rc = sqrt( 1.0 - minInvGain / invGain );
- if( num > 0 ) {
- /* Ensure adjusted reflection coefficient has the original sign */
- rc = -rc;
- }
- invGain = minInvGain;
- reached_max_gain = 1;
- } else {
- invGain = tmp1;
- }
- /* Update the AR coefficients */
- for( k = 0; k < (n + 1) >> 1; k++ ) {
- tmp1 = a[ k ];
- tmp2 = a[ n - k - 1 ];
- a[ k ] = tmp1 + rc * tmp2;
- a[ n - k - 1 ] = tmp2 + rc * tmp1;
- }
- a[ n ] = rc;
- if( reached_max_gain ) {
- /* Reached max prediction gain; set remaining coefficients to zero and exit loop */
- for( k = n + 1; k < D; k++ ) {
- a[ k ] = 0.0;
- }
- break;
- }
- }
- /* Convert to silk_float */
- for( k = 0; k < D; k++ ) {
- af[ k ] = (silk_float)( -a[ k ] );
- }
- nrg = c[ 0 ] * 0.5 * (1.0 - FIND_LPC_COND_FAC);
- /* Subtract energy of preceding samples from C0 */
- for( s = 0; s < nb_subfr; s++ ) {
- nrg -= silk_energy_FLP( x + s * subfr_length, D );
- }
- /* Approximate residual energy */
- nrg *= invGain;
- /* Return approximate residual energy */
- return (silk_float)nrg;
- }
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