82 lines
3.2 KiB
C
82 lines
3.2 KiB
C
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/***********************************************************************
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Copyright (c) 2006-2011, 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, are permitted provided that the following conditions
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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 Internet Society, IETF or IETF Trust, nor the
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names of specific contributors, may be used to endorse or promote
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products derived from this software without specific prior written
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permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS”
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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***********************************************************************/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include "SigProc_FLP.h"
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/* Solve the normal equations using the Levinson-Durbin recursion */
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silk_float silk_levinsondurbin_FLP( /* O prediction error energy */
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silk_float A[], /* O prediction coefficients [order] */
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const silk_float corr[], /* I input auto-correlations [order + 1] */
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const opus_int order /* I prediction order */
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)
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{
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opus_int i, mHalf, m;
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silk_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 = silk_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 = silk_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 = silk_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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