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) );
}