gainquant.c

视频监控vc源代码.对于做视频系统的朋友们很有帮助

/******************************************************************

    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 "gainquant.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;
}