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1 /*********************************************************************** | |
2 Copyright (c) 2006-2011, Skype Limited. All rights reserved. | |
3 Redistribution and use in source and binary forms, with or without | |
4 modification, are permitted provided that the following conditions | |
5 are met: | |
6 - Redistributions of source code must retain the above copyright notice, | |
7 this list of conditions and the following disclaimer. | |
8 - Redistributions in binary form must reproduce the above copyright | |
9 notice, this list of conditions and the following disclaimer in the | |
10 documentation and/or other materials provided with the distribution. | |
11 - Neither the name of Internet Society, IETF or IETF Trust, nor the | |
12 names of specific contributors, may be used to endorse or promote | |
13 products derived from this software without specific prior written | |
14 permission. | |
15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" | |
16 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
17 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
18 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE | |
19 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR | |
20 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF | |
21 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS | |
22 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN | |
23 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) | |
24 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE | |
25 POSSIBILITY OF SUCH DAMAGE. | |
26 ***********************************************************************/ | |
27 | |
28 #ifdef HAVE_CONFIG_H | |
29 #include "config.h" | |
30 #endif | |
31 | |
32 #include "SigProc_FLP.h" | |
33 | |
34 /* Solve the normal equations using the Levinson-Durbin recursion */ | |
35 silk_float silk_levinsondurbin_FLP( /* O prediction error energy
*/ | |
36 silk_float A[], /* O prediction coefficients [
order] */ | |
37 const silk_float corr[], /* I input auto-correlations [ord
er + 1] */ | |
38 const opus_int order /* I prediction order
*/ | |
39 ) | |
40 { | |
41 opus_int i, mHalf, m; | |
42 silk_float min_nrg, nrg, t, km, Atmp1, Atmp2; | |
43 | |
44 min_nrg = 1e-12f * corr[ 0 ] + 1e-9f; | |
45 nrg = corr[ 0 ]; | |
46 nrg = silk_max_float(min_nrg, nrg); | |
47 A[ 0 ] = corr[ 1 ] / nrg; | |
48 nrg -= A[ 0 ] * corr[ 1 ]; | |
49 nrg = silk_max_float(min_nrg, nrg); | |
50 | |
51 for( m = 1; m < order; m++ ) | |
52 { | |
53 t = corr[ m + 1 ]; | |
54 for( i = 0; i < m; i++ ) { | |
55 t -= A[ i ] * corr[ m - i ]; | |
56 } | |
57 | |
58 /* reflection coefficient */ | |
59 km = t / nrg; | |
60 | |
61 /* residual energy */ | |
62 nrg -= km * t; | |
63 nrg = silk_max_float(min_nrg, nrg); | |
64 | |
65 mHalf = m >> 1; | |
66 for( i = 0; i < mHalf; i++ ) { | |
67 Atmp1 = A[ i ]; | |
68 Atmp2 = A[ m - i - 1 ]; | |
69 A[ m - i - 1 ] -= km * Atmp1; | |
70 A[ i ] -= km * Atmp2; | |
71 } | |
72 if( m & 1 ) { | |
73 A[ mHalf ] -= km * A[ mHalf ]; | |
74 } | |
75 A[ m ] = km; | |
76 } | |
77 | |
78 /* return the residual energy */ | |
79 return nrg; | |
80 } | |
81 | |
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