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lpc.c (4295B)
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1 /********************************************************************
2 * *
3 * THIS FILE IS PART OF THE OggVorbis SOFTWARE CODEC SOURCE CODE. *
4 * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS *
5 * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
6 * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. *
7 * *
8 * THE OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2002 *
9 * by the XIPHOPHORUS Company http://www.xiph.org/ *
10 * *
11 ********************************************************************
12
13 function: LPC low level routines
14 last mod: $Id: lpc.c 1919 2005-07-24 14:18:04Z baford $
15
16 ********************************************************************/
17
18 /* Some of these routines (autocorrelator, LPC coefficient estimator)
19 are derived from code written by Jutta Degener and Carsten Bormann;
20 thus we include their copyright below. The entirety of this file
21 is freely redistributable on the condition that both of these
22 copyright notices are preserved without modification. */
23
24 /* Preserved Copyright: *********************************************/
25
26 /* Copyright 1992, 1993, 1994 by Jutta Degener and Carsten Bormann,
27 Technische Universita"t Berlin
28
29 Any use of this software is permitted provided that this notice is not
30 removed and that neither the authors nor the Technische Universita"t
31 Berlin are deemed to have made any representations as to the
32 suitability of this software for any purpose nor are held responsible
33 for any defects of this software. THERE IS ABSOLUTELY NO WARRANTY FOR
34 THIS SOFTWARE.
35
36 As a matter of courtesy, the authors request to be informed about uses
37 this software has found, about bugs in this software, and about any
38 improvements that may be of general interest.
39
40 Berlin, 28.11.1994
41 Jutta Degener
42 Carsten Bormann
43
44 *********************************************************************/
45
46 #include <stdlib.h>
47 #include <string.h>
48 #include <math.h>
49 #include "os.h"
50 #include "smallft.h"
51 #include "lpc.h"
52 #include "scales.h"
53 #include "misc.h"
54
55 /* Autocorrelation LPC coeff generation algorithm invented by
56 N. Levinson in 1947, modified by J. Durbin in 1959. */
57
58 /* Input : n elements of time doamin data
59 Output: m lpc coefficients, excitation energy */
60
61 float vorbis_lpc_from_data(float *data,float *lpci,int n,int m){
62 double *aut=alloca(sizeof(*aut)*(m+1));
63 double *lpc=alloca(sizeof(*lpc)*(m));
64 double error;
65 int i,j;
66
67 /* autocorrelation, p+1 lag coefficients */
68 j=m+1;
69 while(j--){
70 double d=0; /* double needed for accumulator depth */
71 for(i=j;i<n;i++)d+=(double)data[i]*data[i-j];
72 aut[j]=d;
73 }
74
75 /* Generate lpc coefficients from autocorr values */
76
77 error=aut[0];
78
79 for(i=0;i<m;i++){
80 double r= -aut[i+1];
81
82 if(error==0){
83 memset(lpci,0,m*sizeof(*lpci));
84 return 0;
85 }
86
87 /* Sum up this iteration's reflection coefficient; note that in
88 Vorbis we don't save it. If anyone wants to recycle this code
89 and needs reflection coefficients, save the results of 'r' from
90 each iteration. */
91
92 for(j=0;j<i;j++)r-=lpc[j]*aut[i-j];
93 r/=error;
94
95 /* Update LPC coefficients and total error */
96
97 lpc[i]=r;
98 for(j=0;j<i/2;j++){
99 double tmp=lpc[j];
100
101 lpc[j]+=r*lpc[i-1-j];
102 lpc[i-1-j]+=r*tmp;
103 }
104 if(i%2)lpc[j]+=lpc[j]*r;
105
106 error*=1.f-r*r;
107 }
108
109 for(j=0;j<m;j++)lpci[j]=(float)lpc[j];
110
111 /* we need the error value to know how big an impulse to hit the
112 filter with later */
113
114 return error;
115 }
116
117 void vorbis_lpc_predict(float *coeff,float *prime,int m,
118 float *data,long n){
119
120 /* in: coeff[0...m-1] LPC coefficients
121 prime[0...m-1] initial values (allocated size of n+m-1)
122 out: data[0...n-1] data samples */
123
124 long i,j,o,p;
125 float y;
126 float *work=alloca(sizeof(*work)*(m+n));
127
128 if(!prime)
129 for(i=0;i<m;i++)
130 work[i]=0.f;
131 else
132 for(i=0;i<m;i++)
133 work[i]=prime[i];
134
135 for(i=0;i<n;i++){
136 y=0;
137 o=i;
138 p=m;
139 for(j=0;j<m;j++)
140 y-=work[o++]*coeff[--p];
141
142 data[i]=work[o]=y;
143 }
144 }
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