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source: downloads/libvorbis-1.2.0/lib/lpc.c @ 52

Last change on this file since 52 was 16, checked in by landauf, 17 years ago

added libvorbis

File size: 4.2 KB
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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 1994-2007             *
9 * by the Xiph.Org Foundation http://www.xiph.org/                  *
10 *                                                                  *
11 ********************************************************************
12
13  function: LPC low level routines
14  last mod: $Id: lpc.c 13293 2007-07-24 00:09:47Z xiphmont $
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,
27Technische Universita"t Berlin
28
29Any use of this software is permitted provided that this notice is not
30removed and that neither the authors nor the Technische Universita"t
31Berlin are deemed to have made any representations as to the
32suitability of this software for any purpose nor are held responsible
33for any defects of this software. THERE IS ABSOLUTELY NO WARRANTY FOR
34THIS SOFTWARE.
35
36As a matter of courtesy, the authors request to be informed about uses
37this software has found, about bugs in this software, and about any
38improvements that may be of general interest.
39
40Berlin, 28.11.1994
41Jutta Degener
42Carsten 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
61float 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
117void 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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