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/*
vox - a musical real-time vocoder. version 1.0
Copyright (C) 2000  Simon MORLAT (simon.morlat@free.fr)

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
*/

#include "tables.h"
#include "lpc.h"
#define THRES 0.06
#define Dmin 10.81e-3

/* Levinson Durbin algorithm for computing LPC coefficients using 
autocorrelation fonction */
void lev_durb(double *corr,double *lpc_coef)
{
  double k[11],tab[11];
  double err,acc;
  int i,j;  
  double *a=tab;
  double *prev_a=lpc_coef;
  double *exch;
  
  
  /*init vectors*/
  for (i=0;i<11;i++)
  {
      prev_a[i]=0;
      a[i]=0;
  };
  err=corr[0];
  for(i=1;i<11;i++)
  {
      prev_a[0]=1;
      acc=0;
      for(j=0;j<i;j++) 
      {
	  acc=acc+prev_a[j]*corr[i-j];
      };
      a[i]=k[i]=-acc/err;
      for(j=1;j<i;j++)
      {
	  a[j]=prev_a[j]+k[i]*prev_a[i-j];
      };
      err=(1-k[i]*k[i])*err;
      exch=prev_a;
      prev_a=a;
      a=exch;
  };
}

void comp_lpc(double *buf_x,double *corr,double *lpc_coef,int n)
{
  double buffer[n*3];
  double acc,max=0;
  int i,j;
  /* computes LPC analysis for one subframe */
  /* hamming windowing*/
  acc=0;
  for(i=0;i<2*n;i++)
  {
      acc+=buf_x[i]*buf_x[i];
  };
  if (acc>THRES) 
  {
      for(i=0;i<3*n;i++)
      {
	  buffer[i]=buf_x[i-n]*HammingWindowTable[i];
      };
      /* autocorrelation computation*/
      for(i=0;i<11;i++)
      {
	  acc=0;
	  for(j=i;j<n*3;j++)	    
          {
	      acc=acc+buffer[j]*buffer[j-i];
	  };
	  /* correction with binomial coeffs */
	  corr[i]=acc;//*BinomialWindowTable[i];
      };
      corr[0]=corr[0]*(1.0+1.0/1024.0);
      lev_durb(corr,lpc_coef);
  } 
  else
  {
      for(i=0;i<11;i++)
      {
	  lpc_coef[i]=0;
      };
  }
}
  


/* LPC to LSP coefficients conversion */

/* evaluate  function C(x) (whose roots are  LSP coeffs)*/

double evalc(double cw,double *fonc)
{
  double b[7];
  double x,res;
  int k;

  x=cw;
  b[5]=1;
  b[6]=0;
  for(k=4;k>0;k--)
  {
      b[k]=2*x*b[k+1]-b[k+2]+fonc[5-k];
  };
  res=x*b[1]-b[2]+fonc[5]/2;
  return(res);
}



/* converts LPC vector into LSP frequency vector */
/* all LSP frenquencies are in [0;PI] but are normalized to be in [0;1] */
void lpc2lsp(double lpc_coef[],double *f1,double *f2,double lsp_coef[])
{
  
  int i,k=1;
  double *fonc,*prev_f,*f_exch;
  double prev_sign1,sign,prev_sign2;
  double *s, *prev_s,*s_exch;
  double lpc_exp[11];

  /* first computes an additional bandwidth expansion on LPC coeffs*/
  for(i=1;i<11;i++)
  {
      lpc_exp[i]=lpc_coef[i]*BandExpTable[i];
  };
  /* computes the F1 and F2 coeffs*/
  f1[0]=f2[0]=1;
  for(i=0;i<5;i++)
  {
      f1[i+1]=lpc_exp[i+1]+lpc_exp[10-i]-f1[i];
      f2[i+1]=lpc_exp[i+1]-lpc_exp[10-i]+f2[i];
  }; 

   /*find the roots of C(x) alternatively for F1 and F2*/
  fonc=f1;
  prev_f=f2;
  prev_sign1=evalc(1.0,f1);
  prev_sign2=evalc(1.0,f2);
  s=&prev_sign1;
  prev_s=&prev_sign2;
  for(i=1;i<256;i++)
  {
      sign=evalc(CosineTable[i],fonc);
      if ((sign)*(*s)<0)
      {
	  /* interpolate to find root*/
	  lsp_coef[k]=((double)i-(*s)/(sign-(*s)))/256.0;
	  k++;
	  /* chek if all roots are found */
	  if (k==11) i=257;
	  (*s)=sign;
	  /* pointers exchange  */
	  s_exch=s;
	  s=prev_s;
	  prev_s=s_exch;
	  f_exch=fonc;
	  fonc=prev_f;
	  prev_f=f_exch;
       }
       else (*s)=sign;
  }
  /* if here all roots are not found , use  lspDC vector */
  if (k!=11)
  {
      for(i=1;i<11;i++)
      {
	  lsp_coef[i]=LspDcTable[i];
      };
  };
}


/* converts lsp frequencies to lpc coeffs */

void lsp2lpc(double *lsp_coef,double *lpc_coef)
{
   int i,j=0,index,ok=1;
   double lspcos[11],delta,tmp,p_avg;
   double F1[12],F2[12]; /* begin at indice two*/

   F1[0]=0;F1[1]=1;
   F2[0]=0;F2[1]=1;
   /* stability check */
   while(ok && (j<11))
   {
       ok=0;
       for(i=1;i<10;i++)
       {
	   if( (lsp_coef[i+1]-lsp_coef[i]) < Dmin)
	   {
	       ok=1;
	       p_avg=(lsp_coef[i]+lsp_coef[i+1])/2.0;
	       lsp_coef[i]=p_avg-Dmin/2.0;
	       lsp_coef[i+1]=p_avg+Dmin/2.0;
	   };
       };
       j++;
   }
   
   /* first converts lsp frequencies to lsp coefficients */
   for (i=1;i<11;i++)
   {
       /* interpolation */
       tmp=lsp_coef[i]*255.0;
       index=(int)tmp;
       delta=CosineTable[index+1]-CosineTable[index];
       lspcos[i]=CosineTable[index]+delta*(tmp-index);
   };

   for(i=2;i<7;i++)
   {
       F1[i]=-2*lspcos[2*i-3]*F1[i-1]+2*F1[i-2];
       F2[i]=-2*lspcos[2*i-2]*F2[i-1]+2*F2[i-2]; 
       for(j=i-1;j>1;j--)
       {
	   F1[j]=F1[j]-2*lspcos[2*i-3]*F1[j-1]+F1[j-2];
	   F2[j]=F2[j]-2*lspcos[2*i-2]*F2[j-1]+F2[j-2];
       };
   };
   for(i=6;i>1;i--)
   {
       F1[i]=F1[i]+F1[i-1];
       F2[i]=F2[i]-F2[i-1];
   };
   for(i=2;i<7;i++)
   {
       lpc_coef[i-1]=(F1[i]+F2[i])*0.5;
       lpc_coef[i+4]=(F1[8-i]-F2[8-i])*0.5;
   };
   lpc_coef[0]=1;
}