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| - Redistributions in binary form must reproduce the above copyright |
| notice, this list of conditions and the following disclaimer in the |
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| products derived from this software without specific prior written |
| permission. |
| THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” |
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| ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE |
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| ***********************************************************************/ |
| |
| #ifdef HAVE_CONFIG_H |
| #include "config.h" |
| #endif |
| |
| #include "SigProc_FLP.h" |
| |
| /* Solve the normal equations using the Levinson-Durbin recursion */ |
| silk_float silk_levinsondurbin_FLP( /* O prediction error energy */ |
| silk_float A[], /* O prediction coefficients [order] */ |
| const silk_float corr[], /* I input auto-correlations [order + 1] */ |
| const opus_int order /* I prediction order */ |
| ) |
| { |
| opus_int i, mHalf, m; |
| silk_float min_nrg, nrg, t, km, Atmp1, Atmp2; |
| |
| min_nrg = 1e-12f * corr[ 0 ] + 1e-9f; |
| nrg = corr[ 0 ]; |
| nrg = silk_max_float(min_nrg, nrg); |
| A[ 0 ] = corr[ 1 ] / nrg; |
| nrg -= A[ 0 ] * corr[ 1 ]; |
| nrg = silk_max_float(min_nrg, nrg); |
| |
| for( m = 1; m < order; m++ ) |
| { |
| t = corr[ m + 1 ]; |
| for( i = 0; i < m; i++ ) { |
| t -= A[ i ] * corr[ m - i ]; |
| } |
| |
| /* reflection coefficient */ |
| km = t / nrg; |
| |
| /* residual energy */ |
| nrg -= km * t; |
| nrg = silk_max_float(min_nrg, nrg); |
| |
| mHalf = m >> 1; |
| for( i = 0; i < mHalf; i++ ) { |
| Atmp1 = A[ i ]; |
| Atmp2 = A[ m - i - 1 ]; |
| A[ m - i - 1 ] -= km * Atmp1; |
| A[ i ] -= km * Atmp2; |
| } |
| if( m & 1 ) { |
| A[ mHalf ] -= km * A[ mHalf ]; |
| } |
| A[ m ] = km; |
| } |
| |
| /* return the residual energy */ |
| return nrg; |
| } |
| |