asterisk/codecs/ilbc/gainquant.c

 
/****************************************************************** 
 
    iLBC Speech Coder ANSI-C Source Code 
 
    gainquant.c  
 
    Copyright (c) 2001, 
    Global IP Sound AB. 
    All rights reserved. 
 
******************************************************************/ 
 
#include <string.h> 
#include <math.h> 
#include "constants.h" 
#include "filter.h" 
#include "gainquant.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; 
}