gainquant.c

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   /******************************************************************
 
       iLBC Speech Coder ANSI-C Source Code
 
 
 
 
 
 
       gainquant.c
 
       Copyright (C) The Internet Society (2004).
       All Rights Reserved.
 
   ******************************************************************/
 
   #include <string.h>
   #include <math.h>
   #include "constants.h"
   #include "filter.h"
 
   /*----------------------------------------------------------------*
    *  quantizer for the gain in the gain-shape coding of residual
    *---------------------------------------------------------------*/
 
   float gainquant(/* (o) quantized gain value */
       float in,       /* (i) gain value */
       float maxIn,/* (i) maximum of gain value */
       int cblen,      /* (i) number of quantization indices */
       int *index      /* (o) quantization index */
   ){
       int i, tindex;
       float minmeasure,measure, *cb, scale;
 
       /* ensure a lower bound on the scaling factor */
 
       scale=maxIn;
 
       if (scale<0.1) {
           scale=(float)0.1;
       }
 
       /* select the quantization table */
 
       if (cblen == 8) {
           cb = gain_sq3Tbl;
       } else if (cblen == 16) {
           cb = gain_sq4Tbl;
       } else  {
           cb = gain_sq5Tbl;
       }
 
       /* select the best index in the quantization table */
 
       minmeasure=10000000.0;
       tindex=0;
       for (i=0; i<cblen; i++) {
 
 
 
 
 
           measure=(in-scale*cb[i])*(in-scale*cb[i]);
 
           if (measure<minmeasure) {
               tindex=i;
               minmeasure=measure;
           }
       }
       *index=tindex;
 
       /* return the quantized value */
 
       return scale*cb[tindex];
   }
 
   /*----------------------------------------------------------------*
    *  decoder for quantized gains in the gain-shape coding of
    *  residual
    *---------------------------------------------------------------*/
 
   float gaindequant(  /* (o) quantized gain value */
       int index,      /* (i) quantization index */
       float maxIn,/* (i) maximum of unquantized gain */
       int cblen       /* (i) number of quantization indices */
   ){
       float scale;
 
       /* obtain correct scale factor */
 
       scale=(float)fabs(maxIn);
 
       if (scale<0.1) {
           scale=(float)0.1;
       }
 
       /* select the quantization table and return the decoded value */
 
       if (cblen==8) {
           return scale*gain_sq3Tbl[index];
       } else if (cblen==16) {
           return scale*gain_sq4Tbl[index];
       }
       else if (cblen==32) {
           return scale*gain_sq5Tbl[index];
       }
 
       return 0.0;
   }