lpcdecode.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

    LPC_decode.c 

    Copyright (C) The Internet Society (2004). 
    All Rights Reserved.

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

#include <math.h>
#include <string.h>

#include "helpfun.h"
#include "lsf.h"
#include "iLBC_define.h"
#include "LPCdecode.h"
#include "constants.h"

/*---------------------------------------------------------------*
 *  interpolation of lsf coefficients for the decoder
 *--------------------------------------------------------------*/

void LSFinterpolate2a_dec( 
    float *a,           /* (o) lpc coefficients for a sub-frame */
    float *lsf1,    /* (i) first lsf coefficient vector */


    float *lsf2,    /* (i) second lsf coefficient vector */
    float coef,         /* (i) interpolation weight */
    int length          /* (i) length of lsf vectors */
){
    float  lsftmp[LPC_FILTERORDER];
    
    interpolate(lsftmp, lsf1, lsf2, coef, length);
    lsf2a(a, lsftmp);
}

/*---------------------------------------------------------------*
 *  obtain dequantized lsf coefficients from quantization index 
 *--------------------------------------------------------------*/

void SimplelsfDEQ(
    float *lsfdeq,    /* (o) dequantized lsf coefficients */
    int *index,         /* (i) quantization index */
    int lpc_n           /* (i) number of LPCs */
){  
    int i, j, pos, cb_pos;

    /* decode first LSF */
    
    pos = 0;
    cb_pos = 0;
    for (i = 0; i < LSF_NSPLIT; i++) {
        for (j = 0; j < dim_lsfCbTbl[i]; j++) {
            lsfdeq[pos + j] = lsfCbTbl[cb_pos + 
                (long)(index[i])*dim_lsfCbTbl[i] + j];
        }       
        pos += dim_lsfCbTbl[i];
        cb_pos += size_lsfCbTbl[i]*dim_lsfCbTbl[i];
    }

    if (lpc_n>1) {

        /* decode last LSF */

        pos = 0;
        cb_pos = 0;
        for (i = 0; i < LSF_NSPLIT; i++) {
            for (j = 0; j < dim_lsfCbTbl[i]; j++) {
                lsfdeq[LPC_FILTERORDER + pos + j] = 
                    lsfCbTbl[cb_pos + 
                    (long)(index[LSF_NSPLIT + i])*
                    dim_lsfCbTbl[i] + j];
            }       
            pos += dim_lsfCbTbl[i];
            cb_pos += size_lsfCbTbl[i]*dim_lsfCbTbl[i];
        }
    }
}

/*----------------------------------------------------------------*


 *  obtain synthesis and weighting filters form lsf coefficients 
 *---------------------------------------------------------------*/

void DecoderInterpolateLSF( 
    float *syntdenum, /* (o) synthesis filter coefficients */
    float *weightdenum, /* (o) weighting denumerator 
                               coefficients */
    float *lsfdeq,       /* (i) dequantized lsf coefficients */
    int length,         /* (i) length of lsf coefficient vector */
    iLBC_Dec_Inst_t *iLBCdec_inst 
                        /* (i) the decoder state structure */
){
    int    i, pos, lp_length;
    float  lp[LPC_FILTERORDER + 1], *lsfdeq2;
        
    lsfdeq2 = lsfdeq + length;
    lp_length = length + 1;
    
    if (iLBCdec_inst->mode==30) {
        /* sub-frame 1: Interpolation between old and first */

        LSFinterpolate2a_dec(lp, iLBCdec_inst->lsfdeqold, lsfdeq, 
            lsf_weightTbl_30ms[0], length);
        memcpy(syntdenum,lp,lp_length*sizeof(float));
        bwexpand(weightdenum, lp, LPC_CHIRP_WEIGHTDENUM, 
            lp_length);

        /* sub-frames 2 to 6: interpolation between first 
           and last LSF */
    
        pos = lp_length;
        for (i = 1; i < 6; i++) {
            LSFinterpolate2a_dec(lp, lsfdeq, lsfdeq2, 
                lsf_weightTbl_30ms[i], length);
            memcpy(syntdenum + pos,lp,lp_length*sizeof(float));
            bwexpand(weightdenum + pos, lp, 
                LPC_CHIRP_WEIGHTDENUM, lp_length);
            pos += lp_length;
        }
    }
    else {
        pos = 0;
        for (i = 0; i < iLBCdec_inst->nsub; i++) {
            LSFinterpolate2a_dec(lp, iLBCdec_inst->lsfdeqold, 
                lsfdeq, lsf_weightTbl_20ms[i], length);
            memcpy(syntdenum+pos,lp,lp_length*sizeof(float));
            bwexpand(weightdenum+pos, lp, LPC_CHIRP_WEIGHTDENUM, 
                lp_length);
            pos += lp_length;
        }
    }
    
    /* update memory */



    if (iLBCdec_inst->mode==30)
        memcpy(iLBCdec_inst->lsfdeqold, lsfdeq2, 
                    length*sizeof(float));
    else
        memcpy(iLBCdec_inst->lsfdeqold, lsfdeq, 
                    length*sizeof(float));

}