michael@0: /***********************************************************************
michael@0: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
michael@0: Redistribution and use in source and binary forms, with or without
michael@0: modification, are permitted provided that the following conditions
michael@0: are met:
michael@0: - Redistributions of source code must retain the above copyright notice,
michael@0: this list of conditions and the following disclaimer.
michael@0: - Redistributions in binary form must reproduce the above copyright
michael@0: notice, this list of conditions and the following disclaimer in the
michael@0: documentation and/or other materials provided with the distribution.
michael@0: - Neither the name of Internet Society, IETF or IETF Trust, nor the
michael@0: names of specific contributors, may be used to endorse or promote
michael@0: products derived from this software without specific prior written
michael@0: permission.
michael@0: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
michael@0: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
michael@0: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
michael@0: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
michael@0: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
michael@0: CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
michael@0: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
michael@0: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
michael@0: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
michael@0: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
michael@0: POSSIBILITY OF SUCH DAMAGE.
michael@0: ***********************************************************************/
michael@0: 
michael@0: #ifdef HAVE_CONFIG_H
michael@0: #include "config.h"
michael@0: #endif
michael@0: 
michael@0: #include "SigProc_FLP.h"
michael@0: 
michael@0: /* Solve the normal equations using the Levinson-Durbin recursion */
michael@0: silk_float silk_levinsondurbin_FLP(         /* O    prediction error energy                                     */
michael@0:     silk_float          A[],                /* O    prediction coefficients    [order]                          */
michael@0:     const silk_float    corr[],             /* I    input auto-correlations [order + 1]                         */
michael@0:     const opus_int      order               /* I    prediction order                                            */
michael@0: )
michael@0: {
michael@0:     opus_int   i, mHalf, m;
michael@0:     silk_float min_nrg, nrg, t, km, Atmp1, Atmp2;
michael@0: 
michael@0:     min_nrg = 1e-12f * corr[ 0 ] + 1e-9f;
michael@0:     nrg = corr[ 0 ];
michael@0:     nrg = silk_max_float(min_nrg, nrg);
michael@0:     A[ 0 ] = corr[ 1 ] / nrg;
michael@0:     nrg -= A[ 0 ] * corr[ 1 ];
michael@0:     nrg = silk_max_float(min_nrg, nrg);
michael@0: 
michael@0:     for( m = 1; m < order; m++ )
michael@0:     {
michael@0:         t = corr[ m + 1 ];
michael@0:         for( i = 0; i < m; i++ ) {
michael@0:             t -= A[ i ] * corr[ m - i ];
michael@0:         }
michael@0: 
michael@0:         /* reflection coefficient */
michael@0:         km = t / nrg;
michael@0: 
michael@0:         /* residual energy */
michael@0:         nrg -= km * t;
michael@0:         nrg = silk_max_float(min_nrg, nrg);
michael@0: 
michael@0:         mHalf = m >> 1;
michael@0:         for( i = 0; i < mHalf; i++ ) {
michael@0:             Atmp1 = A[ i ];
michael@0:             Atmp2 = A[ m - i - 1 ];
michael@0:             A[ m - i - 1 ] -= km * Atmp1;
michael@0:             A[ i ]         -= km * Atmp2;
michael@0:         }
michael@0:         if( m & 1 ) {
michael@0:             A[ mHalf ]     -= km * A[ mHalf ];
michael@0:         }
michael@0:         A[ m ] = km;
michael@0:     }
michael@0: 
michael@0:     /* return the residual energy */
michael@0:     return nrg;
michael@0: }
michael@0: