gainquant.cxx

来自「MiniSip Client with DomainKeys Authentic」· CXX 代码 · 共 108 行

//A.22 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" 
    
   /*----------------------------------------------------------------* 
    *  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; 
   }