interpretor/libsndfile-1.0.25/src/GSM610/preprocess.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 #include        <stdio.h>
   8 #include        <assert.h>
   9
  10 #include "gsm610_priv.h"
  11
  12 /*      4.2.0 .. 4.2.3  PREPROCESSING SECTION
  13  *
  14  *      After A-law to linear conversion (or directly from the
  15  *      Ato D converter) the following scaling is assumed for
  16  *      input to the RPE-LTP algorithm:
  17  *
  18  *      in:  0.1.....................12
  19  *           S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
  20  *
  21  *      Where S is the sign bit, v a valid bit, and * a "don't care" bit.
  22  *      The original signal is called sop[..]
  23  *
  24  *      out:   0.1................... 12
  25  *           S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
  26  */
  27
  28
  29 void Gsm_Preprocess (
  30         struct gsm_state * S,
  31         word             * s,
  32         word             * so )         /* [0..159]     IN/OUT  */
  33 {
  34
  35         word       z1 = S->z1;
  36         longword L_z2 = S->L_z2;
  37         word       mp = S->mp;
  38
  39         word            s1;
  40         longword      L_s2;
  41
  42         longword      L_temp;
  43
  44         word            msp, lsp;
  45         word            SO;
  46
  47         register int            k = 160;
  48
  49         while (k--) {
  50
  51         /*  4.2.1   Downscaling of the input signal
  52          */
  53                 SO = SASR_W( *s, 3 ) << 2;
  54                 s++;
  55
  56                 assert (SO >= -0x4000); /* downscaled by     */
  57                 assert (SO <=  0x3FFC); /* previous routine. */
  58
  59
  60         /*  4.2.2   Offset compensation
  61          *
  62          *  This part implements a high-pass filter and requires extended
  63          *  arithmetic precision for the recursive part of this filter.
  64          *  The input of this procedure is the array so[0...159] and the
  65          *  output the array sof[ 0...159 ].
  66          */
  67                 /*   Compute the non-recursive part
  68                  */
  69
  70                 s1 = SO - z1;                   /* s1 = gsm_sub( *so, z1 ); */
  71                 z1 = SO;
  72
  73                 assert(s1 != MIN_WORD);
  74
  75                 /*   Compute the recursive part
  76                  */
  77                 L_s2 = s1;
  78                 L_s2 <<= 15;
  79
  80                 /*   Execution of a 31 bv 16 bits multiplication
  81                  */
  82
  83                 msp = SASR_L( L_z2, 15 );
  84                 lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */
  85
  86                 L_s2  += GSM_MULT_R( lsp, 32735 );
  87                 L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/
  88                 L_z2   = GSM_L_ADD( L_temp, L_s2 );
  89
  90                 /*    Compute sof[k] with rounding
  91                  */
  92                 L_temp = GSM_L_ADD( L_z2, 16384 );
  93
  94         /*   4.2.3  Preemphasis
  95          */
  96
  97                 msp   = GSM_MULT_R( mp, -28180 );
  98                 mp    = SASR_L( L_temp, 15 );
  99                 *so++ = GSM_ADD( mp, msp );
 100         }
 101
 102         S->z1   = z1;
 103         S->L_z2 = L_z2;
 104         S->mp   = mp;
 105 }