libs/gsm/src/code.c

   1 /*
   2  * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
   3  * Universitaet Berlin.  See the accompanying file "COPYRIGHT" for
   4  * details.  THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
   5  */
   6
   7 /* $Header: /tmp_amd/presto/export/kbs/jutta/src/gsm/RCS/code.c,v 1.3 1996/07/02 09:59:05 jutta Exp $ */
   8
   9 #include <string.h>
  10
  11 #include        "private.h"
  12 #include        "gsm.h"
  13 #include        "proto.h"
  14
  15 /*
  16  *  4.2 FIXED POINT IMPLEMENTATION OF THE RPE-LTP CODER
  17  */
  18
  19 void Gsm_Coder P8((S,s,LARc,Nc,bc,Mc,xmaxc,xMc),
  20
  21         struct gsm_state        * S,
  22
  23         word    * s,    /* [0..159] samples                     IN      */
  24
  25 /*
  26  * The RPE-LTD coder works on a frame by frame basis.  The length of
  27  * the frame is equal to 160 samples.  Some computations are done
  28  * once per frame to produce at the output of the coder the
  29  * LARc[1..8] parameters which are the coded LAR coefficients and
  30  * also to realize the inverse filtering operation for the entire
  31  * frame (160 samples of signal d[0..159]).  These parts produce at
  32  * the output of the coder:
  33  */
  34
  35         word    * LARc, /* [0..7] LAR coefficients              OUT     */
  36
  37 /*
  38  * Procedure 4.2.11 to 4.2.18 are to be executed four times per
  39  * frame.  That means once for each sub-segment RPE-LTP analysis of
  40  * 40 samples.  These parts produce at the output of the coder:
  41  */
  42
  43         word    * Nc,   /* [0..3] LTP lag                       OUT     */
  44         word    * bc,   /* [0..3] coded LTP gain                OUT     */
  45         word    * Mc,   /* [0..3] RPE grid selection            OUT     */
  46         word    * xmaxc,/* [0..3] Coded maximum amplitude       OUT     */
  47         word    * xMc   /* [13*4] normalized RPE samples        OUT     */
  48 )
  49 {
  50         int     k;
  51         word    * dp  = S->dp0 + 120;   /* [ -120...-1 ] */
  52         word    * dpp = dp;             /* [ 0...39 ]    */
  53
  54         word    so[160];
  55
  56         Gsm_Preprocess                  (S, s, so);
  57         Gsm_LPC_Analysis                (S, so, LARc);
  58         Gsm_Short_Term_Analysis_Filter  (S, LARc, so);
  59
  60         for (k = 0; k <= 3; k++, xMc += 13) {
  61
  62                 Gsm_Long_Term_Predictor ( S,
  63                                          so+k*40, /* d      [0..39] IN  */
  64                                          dp,      /* dp  [-120..-1] IN  */
  65                                         S->e + 5, /* e      [0..39] OUT */
  66                                         dpp,      /* dpp    [0..39] OUT */
  67                                          Nc++,
  68                                          bc++);
  69
  70                 Gsm_RPE_Encoding        ( S,
  71                                         S->e + 5,/* e     ][0..39][ IN/OUT */
  72                                           xmaxc++, Mc++, xMc );
  73                 /*
  74                  * Gsm_Update_of_reconstructed_short_time_residual_signal
  75                  *                      ( dpp, S->e + 5, dp );
  76                  */
  77
  78                 { register int i;
  79                   register longword ltmp;
  80                   for (i = 0; i <= 39; i++)
  81                         dp[ i ] = GSM_ADD( S->e[5 + i], dpp[i] );
  82                 }
  83                 dp  += 40;
  84                 dpp += 40;
  85
  86         }
  87         (void)memcpy( (char *)S->dp0, (char *)(S->dp0 + 160),
  88                 120 * sizeof(*S->dp0) );
  89 }