pred_lt3.c

语音压缩编码中的g729p编码程序

/*
   ITU-T G.729 Annex C - Reference C code for floating point
                         implementation of G.729
                         Version 1.01 of 15.September.98
*/

/*
----------------------------------------------------------------------
                    COPYRIGHT NOTICE
----------------------------------------------------------------------
   ITU-T G.729 Annex C ANSI C source code
   Copyright (C) 1998, AT&T, France Telecom, NTT, University of
   Sherbrooke.  All rights reserved.

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

/*
 File : PRED_LT3.C
*/

#include "typedef.h"
#include "ld8k.h"
#include "tab_ld8k.h"

/*-------------------------------------------------------------------*
* Function  Pred_lt_3()                                             *
*           ~~~~~~~~~~~                                             *
*-------------------------------------------------------------------*
* Compute the result of long term prediction with fractional        *
* interpolation of resolution 1/3.                                  *
*                                                                   *
* On return exc[0..L_subfr-1] contains the interpolated signal      *
*   (adaptive codebook excitation)                                  *
*-------------------------------------------------------------------*/

void pred_lt_3(         /* Compute adaptive codebook                       */
    FLOAT exc[],          /* in/out: excitation vector, exc[0:l_sub-1] = out */
    int t0,               /* input : pitch lag                               */
    int frac,             /* input : Fraction of pitch lag (-1, 0, 1)  / 3   */
    int l_subfr           /* input : length of subframe.                     */
)
{
    int   i, j, k;
    FLOAT s, *x0, *x1, *x2, *c1, *c2;
    
    x0 = &exc[-t0];
    
    frac = -frac;
    if (frac < 0) {
        frac += UP_SAMP;
        x0--;
    }
    
    for (j=0; j<l_subfr; j++)
    {
        x1 = x0++;
        x2 = x0;
        c1 = &inter_3l[frac];
        c2 = &inter_3l[UP_SAMP-frac];
        
        s = (F)0.0;
        for(i=0, k=0; i< L_INTER10; i++, k+=UP_SAMP)
            s+= x1[-i] * c1[k] + x2[i] * c2[k];
        
        exc[j] = s;
    }
    
    return;
}