code.c

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/*
 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
 * Universitaet Berlin.  See the accompanying file "COPYRIGHT" for
 * details.  THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
 */

/* $Header$ */

#include "config.h"

#ifdef   HAS_STRING_H
#include <string.h>
#else
#  include "proto.h"
   extern char * memcpy P((char *, char *, int));
#endif

#include "private.h"
#include "gsm.h"
#include "proto.h"

/*
 *  4.2 FIXED POINT IMPLEMENTATION OF THE RPE-LTP CODER
 */

void Gsm_Coder P8((S,s,LARc,Nc,bc,Mc,xmaxc,xMc),

   struct gsm_state  * S,

   word  * s,  /* [0..159] samples        IN */

/*
 * The RPE-LTD coder works on a frame by frame basis.  The length of
 * the frame is equal to 160 samples.  Some computations are done
 * once per frame to produce at the output of the coder the
 * LARc[1..8] parameters which are the coded LAR coefficients and
 * also to realize the inverse filtering operation for the entire
 * frame (160 samples of signal d[0..159]).  These parts produce at
 * the output of the coder:
 */

   word  * LARc,  /* [0..7] LAR coefficients    OUT   */

/*
 * Procedure 4.2.11 to 4.2.18 are to be executed four times per
 * frame.  That means once for each sub-segment RPE-LTP analysis of
 * 40 samples.  These parts produce at the output of the coder:
 */

   word  * Nc, /* [0..3] LTP lag       OUT   */
   word  * bc, /* [0..3] coded LTP gain      OUT   */
   word  * Mc, /* [0..3] RPE grid selection     OUT     */
   word  * xmaxc,/* [0..3] Coded maximum amplitude OUT   */
   word  * xMc /* [13*4] normalized RPE samples OUT   */
)
{
   int   k;
   word  * dp  = S->dp0 + 120;   /* [ -120...-1 ] */
   word  * dpp = dp;    /* [ 0...39 ]   */

   word  e[50];

   word  so[160];

   memset(e,0,sizeof e);
   Gsm_Preprocess       (S, s, so);
   Gsm_LPC_Analysis     (S, so, LARc);
   Gsm_Short_Term_Analysis_Filter   (S, LARc, so);

   for (k = 0; k <= 3; k++, xMc += 13) {

      Gsm_Long_Term_Predictor ( S,
                so+k*40, /* d      [0..39] IN   */
                dp,    /* dp  [-120..-1] IN  */
               e + 5,     /* e      [0..39] OUT */
               dpp,    /* dpp    [0..39] OUT */
                Nc++,
                bc++);

      Gsm_RPE_Encoding  ( S,
               e + 5,   /* e    ][0..39][ IN/OUT */
                 xmaxc++, Mc++, xMc );
      /*
       * Gsm_Update_of_reconstructed_short_time_residual_signal
       *       ( dpp, e + 5, dp );
       */

      { register int i;
        for (i = 0; i <= 39; i++)
         dp[ i ] = GSM_ADD( e[5 + i], dpp[i] );
      }
      dp  += 40;
      dpp += 40;

   }
   (void)memcpy( (char *)S->dp0, (char *)(S->dp0 + 160),
      120 * sizeof(*S->dp0) );
}