codecs/ilbc/gainquant.c

   1
   2 /******************************************************************
   3
   4     iLBC Speech Coder ANSI-C Source Code
   5
   6     gainquant.c
   7
   8     Copyright (C) The Internet Society (2004).
   9     All Rights Reserved.
  10
  11
  12
  13 ******************************************************************/
  14
  15 #include <string.h>
  16 #include <math.h>
  17 #include "constants.h"
  18 #include "gainquant.h"
  19 #include "filter.h"
  20
  21 /*----------------------------------------------------------------*
  22  *  quantizer for the gain in the gain-shape coding of residual
  23  *---------------------------------------------------------------*/
  24
  25 float gainquant(/* (o) quantized gain value */
  26     float in,       /* (i) gain value */
  27     float maxIn,/* (i) maximum of gain value */
  28     int cblen,      /* (i) number of quantization indices */
  29     int *index      /* (o) quantization index */
  30 ){
  31     int i, tindex;
  32     float minmeasure,measure, *cb, scale;
  33
  34     /* ensure a lower bound on the scaling factor */
  35
  36     scale=maxIn;
  37
  38     if (scale<0.1) {
  39         scale=(float)0.1;
  40     }
  41
  42     /* select the quantization table */
  43
  44     if (cblen == 8) {
  45         cb = gain_sq3Tbl;
  46     } else if (cblen == 16) {
  47         cb = gain_sq4Tbl;
  48     } else  {
  49         cb = gain_sq5Tbl;
  50     }
  51
  52     /* select the best index in the quantization table */
  53
  54     minmeasure=10000000.0;
  55     tindex=0;
  56     for (i=0; i<cblen; i++) {
  57         measure=(in-scale*cb[i])*(in-scale*cb[i]);
  58
  59         if (measure<minmeasure) {
  60             tindex=i;
  61             minmeasure=measure;
  62         }
  63     }
  64     *index=tindex;
  65
  66     /* return the quantized value */
  67
  68
  69
  70     return scale*cb[tindex];
  71 }
  72
  73 /*----------------------------------------------------------------*
  74  *  decoder for quantized gains in the gain-shape coding of
  75  *  residual
  76  *---------------------------------------------------------------*/
  77
  78 float gaindequant(  /* (o) quantized gain value */
  79     int index,      /* (i) quantization index */
  80     float maxIn,/* (i) maximum of unquantized gain */
  81     int cblen       /* (i) number of quantization indices */
  82 ){
  83     float scale;
  84
  85     /* obtain correct scale factor */
  86
  87     scale=(float)fabs(maxIn);
  88
  89     if (scale<0.1) {
  90         scale=(float)0.1;
  91     }
  92
  93     /* select the quantization table and return the decoded value */
  94
  95     if (cblen==8) {
  96         return scale*gain_sq3Tbl[index];
  97     } else if (cblen==16) {
  98         return scale*gain_sq4Tbl[index];
  99     }
 100     else if (cblen==32) {
 101         return scale*gain_sq5Tbl[index];
 102     }
 103
 104     return 0.0;
 105 }
 106
 107