/*
********************************************************************************
*
*      GSM AMR-NB speech codec   R98   Version 7.6.0   December 12, 2001
*                                R99   Version 3.3.0                
*                                REL-4 Version 4.1.0                
*
********************************************************************************
*
*      File             : a_refl.c
*      Purpose          : Convert from direct form coefficients to 
*                         reflection coefficients
*
********************************************************************************
*/
/*
********************************************************************************
*                         MODULE INCLUDE FILE AND VERSION ID
********************************************************************************
*/
#include "a_refl.h"
const char a_refl_id[] = "@(#)$Id $" a_refl_h;
 

/*
********************************************************************************
*                         INCLUDE FILES
********************************************************************************
*/
#include "typedef.h"
#include "basic_op.h"
#include "oper_32b.h"
#include "count.h"
#include "cnst.h"

/*
********************************************************************************
*                         LOCAL VARIABLES AND TABLES
********************************************************************************
*/

/*
********************************************************************************
*                         PUBLIC PROGRAM CODE
********************************************************************************
*/
/*
**************************************************************************
*
*  Function    : A_Refl
*
**************************************************************************
*/ 
void A_Refl(
   Word16 a[],	      /* i   : Directform coefficients */
   Word16 refl[]      /* o   : Reflection coefficients */
)
{				       
   /* local variables */
   Word16 i,j;
   Word16 aState[M];
   Word16 bState[M];
   Word16 normShift;
   Word16 normProd;
   Word32 L_acc;
   Word16 scale;
   Word32 L_temp;
   Word16 temp;
   Word16 mult_ex;

   /* initialize states */
   for (i = 0; i < M; i++)
   {
      aState[i] = a[i];                         move16 ();
   }
   
   /* backward Levinson recursion */
   for (i = M-1; i >= 0; i--)
   {
      if (sub_ex(abs_s_ex(aState[i]), 4096) >= 0)
      {
         goto ExitRefl;
      }
      
      refl[i] = shl_ex(aState[i], 3);

      L_temp = L_mult_ex(refl[i], refl[i]);
      L_acc = L_sub_ex(MAX_32, L_temp);
      
      normShift = norm_l_ex(L_acc);
      scale = sub_ex(15, normShift);
      
      L_acc = L_shl_ex(L_acc, normShift);
      normProd = round_ex(L_acc);

      mult_ex = div_s(16384, normProd);
      
      for (j = 0; j < i; j++)
      {
         L_acc = L_deposit_h_ex(aState[j]);
         L_acc = L_msu_ex(L_acc, refl[i], aState[i-j-1]);
         
         temp = round_ex(L_acc);
         L_temp = L_mult_ex(mult_ex, temp);
         L_temp = L_shr_r_ex(L_temp, scale);
         
         if (L_sub_ex(L_abs_ex(L_temp), 32767) > 0)
         {
            goto ExitRefl;
         }
         
         bState[j] = extract_l_ex(L_temp);
      }
      
      for (j = 0; j < i; j++)
      {
         aState[j] = bState[j];              move16 ();
      }
   }
   return;

ExitRefl:
   for (i = 0; i < M; i++)
   {
      refl[i] = 0;                           move16 ();
   }
}