The Tor Browser: media/libvorbis/lib/vorbis

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revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

     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 1994-2009             *

     9  * by the Xiph.Org Foundation http://www.xiph.org/                  *

    10  *                                                                  *

    11  ********************************************************************

    13   function: LPC low level routines

    14   last mod: $Id: lpc.c 16227 2009-07-08 06:58:46Z xiphmont $

    16  ********************************************************************/

    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.  */

    24 /* Preserved Copyright: *********************************************/

    26 /* Copyright 1992, 1993, 1994 by Jutta Degener and Carsten Bormann,

    27 Technische Universita"t Berlin

    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.

    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.

    40 Berlin, 28.11.1994

    41 Jutta Degener

    42 Carsten Bormann

    44 *********************************************************************/

    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"

    55 /* Autocorrelation LPC coeff generation algorithm invented by

    56    N. Levinson in 1947, modified by J. Durbin in 1959. */

    58 /* Input : n elements of time doamin data

    59    Output: m lpc coefficients, excitation energy */

    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   double epsilon;

    66   int i,j;

    68   /* autocorrelation, p+1 lag coefficients */

    69   j=m+1;

    70   while(j--){

    71     double d=0; /* double needed for accumulator depth */

    72     for(i=j;i<n;i++)d+=(double)data[i]*data[i-j];

    73     aut[j]=d;

    74   }

    76   /* Generate lpc coefficients from autocorr values */

    78   /* set our noise floor to about -100dB */

    79   error=aut[0] * (1. + 1e-10);

    80   epsilon=1e-9*aut[0]+1e-10;

    82   for(i=0;i<m;i++){

    83     double r= -aut[i+1];

    85     if(error<epsilon){

    86       memset(lpc+i,0,(m-i)*sizeof(*lpc));

    87       goto done;

    88     }

    90     /* Sum up this iteration's reflection coefficient; note that in

    91        Vorbis we don't save it.  If anyone wants to recycle this code

    92        and needs reflection coefficients, save the results of 'r' from

    93        each iteration. */

    95     for(j=0;j<i;j++)r-=lpc[j]*aut[i-j];

    96     r/=error;

    98     /* Update LPC coefficients and total error */

   100     lpc[i]=r;

   101     for(j=0;j<i/2;j++){

   102       double tmp=lpc[j];

   104       lpc[j]+=r*lpc[i-1-j];

   105       lpc[i-1-j]+=r*tmp;

   106     }

   107     if(i&1)lpc[j]+=lpc[j]*r;

   109     error*=1.-r*r;

   111   }

   113  done:

   115   /* slightly damp the filter */

   116   {

   117     double g = .99;

   118     double damp = g;

   119     for(j=0;j<m;j++){

   120       lpc[j]*=damp;

   121       damp*=g;

   122     }

   123   }

   125   for(j=0;j<m;j++)lpci[j]=(float)lpc[j];

   127   /* we need the error value to know how big an impulse to hit the

   128      filter with later */

   130   return error;

   131 }

   133 void vorbis_lpc_predict(float *coeff,float *prime,int m,

   134                      float *data,long n){

   136   /* in: coeff[0...m-1] LPC coefficients

   137          prime[0...m-1] initial values (allocated size of n+m-1)

   138     out: data[0...n-1] data samples */

   140   long i,j,o,p;

   141   float y;

   142   float *work=alloca(sizeof(*work)*(m+n));

   144   if(!prime)

   145     for(i=0;i<m;i++)

   146       work[i]=0.f;

   147   else

   148     for(i=0;i<m;i++)

   149       work[i]=prime[i];

   151   for(i=0;i<n;i++){

   152     y=0;

   153     o=i;

   154     p=m;

   155     for(j=0;j<m;j++)

   156       y-=work[o++]*coeff[--p];

   158     data[i]=work[o]=y;

   159   }

   160 }

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