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78 lines
3.2 KiB
C
78 lines
3.2 KiB
C
/***********************************************************************
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Copyright (c) 2006-2012, Skype Limited. All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, (subject to the limitations in the disclaimer below)
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are permitted provided that the following conditions are met:
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- Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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- Neither the name of Skype Limited, nor the names of specific
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contributors, may be used to endorse or promote products derived from
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this software without specific prior written permission.
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NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED
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BY THIS LICENSE. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
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BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
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ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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***********************************************************************/
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#include "SKP_Silk_SigProc_FLP.h"
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/* Solve the normal equations using the Levinson-Durbin recursion */
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SKP_float SKP_Silk_levinsondurbin_FLP( /* O prediction error energy */
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SKP_float A[], /* O prediction coefficients [order] */
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const SKP_float corr[], /* I input auto-correlations [order + 1] */
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const SKP_int order /* I prediction order */
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)
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{
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SKP_int i, mHalf, m;
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SKP_float min_nrg, nrg, t, km, Atmp1, Atmp2;
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min_nrg = 1e-12f * corr[ 0 ] + 1e-9f;
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nrg = corr[ 0 ];
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nrg = SKP_max_float(min_nrg, nrg);
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A[ 0 ] = corr[ 1 ] / nrg;
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nrg -= A[ 0 ] * corr[ 1 ];
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nrg = SKP_max_float(min_nrg, nrg);
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for( m = 1; m < order; m++ )
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{
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t = corr[ m + 1 ];
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for( i = 0; i < m; i++ ) {
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t -= A[ i ] * corr[ m - i ];
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}
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/* reflection coefficient */
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km = t / nrg;
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/* residual energy */
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nrg -= km * t;
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nrg = SKP_max_float(min_nrg, nrg);
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mHalf = m >> 1;
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for( i = 0; i < mHalf; i++ ) {
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Atmp1 = A[ i ];
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Atmp2 = A[ m - i - 1 ];
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A[ m - i - 1 ] -= km * Atmp1;
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A[ i ] -= km * Atmp2;
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}
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if( m & 1 ) {
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A[ mHalf ] -= km * A[ mHalf ];
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}
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A[ m ] = km;
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}
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/* return the residual energy */
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return nrg;
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}
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