interpretor/libsndfile-1.0.25/src/GSM610/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
   8 #include        <stdlib.h>
   9 #include        <string.h>
  10
  11 #include        "gsm610_priv.h"
  12
  13 /*
  14  *  4.2 FIXED POINT IMPLEMENTATION OF THE RPE-LTP CODER
  15  */
  16
  17 void Gsm_Coder (
  18
  19         struct gsm_state        * State,
  20
  21         word    * s,    /* [0..159] samples                     IN      */
  22
  23 /*
  24  * The RPE-LTD coder works on a frame by frame basis.  The length of
  25  * the frame is equal to 160 samples.  Some computations are done
  26  * once per frame to produce at the output of the coder the
  27  * LARc[1..8] parameters which are the coded LAR coefficients and
  28  * also to realize the inverse filtering operation for the entire
  29  * frame (160 samples of signal d[0..159]).  These parts produce at
  30  * the output of the coder:
  31  */
  32
  33         word    * LARc, /* [0..7] LAR coefficients              OUT     */
  34
  35 /*
  36  * Procedure 4.2.11 to 4.2.18 are to be executed four times per
  37  * frame.  That means once for each sub-segment RPE-LTP analysis of
  38  * 40 samples.  These parts produce at the output of the coder:
  39  */
  40
  41         word    * Nc,   /* [0..3] LTP lag                       OUT     */
  42         word    * bc,   /* [0..3] coded LTP gain                OUT     */
  43         word    * Mc,   /* [0..3] RPE grid selection            OUT     */
  44         word    * xmaxc,/* [0..3] Coded maximum amplitude       OUT     */
  45         word    * xMc   /* [13*4] normalized RPE samples        OUT     */
  46 )
  47 {
  48         int     k;
  49         word    * dp  = State->dp0 + 120;       /* [ -120...-1 ] */
  50         word    * dpp = dp;             /* [ 0...39 ]    */
  51
  52         word    so[160];
  53
  54         Gsm_Preprocess                  (State, s, so);
  55         Gsm_LPC_Analysis                (State, so, LARc);
  56         Gsm_Short_Term_Analysis_Filter  (State, LARc, so);
  57
  58         for (k = 0; k <= 3; k++, xMc += 13) {
  59
  60                 Gsm_Long_Term_Predictor ( State,
  61                                          so+k*40, /* d      [0..39] IN  */
  62                                          dp,      /* dp  [-120..-1] IN  */
  63                                         State->e + 5,     /* e      [0..39] OUT */
  64                                         dpp,      /* dpp    [0..39] OUT */
  65                                          Nc++,
  66                                          bc++);
  67
  68                 Gsm_RPE_Encoding        ( /*-S,-*/
  69                                         State->e + 5,   /* e      ][0..39][ IN/OUT */
  70                                           xmaxc++, Mc++, xMc );
  71                 /*
  72                  * Gsm_Update_of_reconstructed_short_time_residual_signal
  73                  *                      ( dpp, State->e + 5, dp );
  74                  */
  75
  76                 { register int i;
  77                   for (i = 0; i <= 39; i++)
  78                         dp[ i ] = GSM_ADD( State->e[5 + i], dpp[i] );
  79                 }
  80                 dp  += 40;
  81                 dpp += 40;
  82
  83         }
  84         (void)memcpy( (char *)State->dp0, (char *)(State->dp0 + 160),
  85                 120 * sizeof(*State->dp0) );
  86 }
  87