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;
 }