gc_pred.c

arm音频编解码库

        ener = MEAN_ENER_MR122; move32 ();                  /* Q24 (Q17) */
        for (i = 0; i < NPRED; i++)
        {
            ener = L_mac (ener, st->past_qua_en_MR122[i], pred_MR122[i]);
                                                     /* Q10 * Q13 -> Q24 */
                                                     /* Q10 * Q6  -> Q17 */
        }

        /*-------------------------------------------------------------------*
         *  predicted codebook gain                                          *
         *  ~~~~~~~~~~~~~~~~~~~~~~~                                          *
         *  gc0     = Pow10( (ener*constant - ener_code*constant) / 20 )     *
         *          = Pow2(ener-ener_code)                                   *
         *          = Pow2(int(d)+frac(d))                                   *
         *                                                                   *
         *  (store exp and frac for pow2())                                  *
         *-------------------------------------------------------------------*/

        ener = L_shr (L_sub (ener, ener_code), 1);                /* Q16 */
        L_Extract(ener, exp_gcode0, frac_gcode0);
    }
    else /* all modes except 12.2 */
    {
        Word32 L_tmp;
        Word16 exp_code, gcode0;
        
        /*-----------------------------------------------------------------*
         *  Compute: means_ener - 10log10(ener_code/ L_sufr)               *
         *-----------------------------------------------------------------*/

        exp_code = norm_l (ener_code);
        ener_code = L_shl (ener_code, exp_code);
        
        /* Log2 = log2 + 27 */
        Log2_norm (ener_code, exp_code, &exp, &frac);
        
        /* fact = 10/log2(10) = 3.01 = 24660 Q13 */
        L_tmp = Mpy_32_16(exp, frac, -24660); /* Q0.Q15 * Q13 -> Q14 */

        /*   L_tmp = means_ener - 10log10(ener_code/L_SUBFR)
         *         = means_ener - 10log10(ener_code) + 10log10(L_SUBFR)
         *         = K - fact * Log2(ener_code)
         *         = K - fact * log2(ener_code) - fact*27
         *
         *   ==> K = means_ener + fact*27 + 10log10(L_SUBFR)
         *
         *   means_ener =       33    =  540672    Q14  (MR475, MR515, MR59)
         *   means_ener =       28.75 =  471040    Q14  (MR67)
         *   means_ener =       30    =  491520    Q14  (MR74)
         *   means_ener =       36    =  589824    Q14  (MR795)
         *   means_ener =       33    =  540672    Q14  (MR102)         
         *   10log10(L_SUBFR) = 16.02 =  262481.51 Q14
         *   fact * 27                = 1331640    Q14
         *   -----------------------------------------
         *   (MR475, MR515, MR59)   K = 2134793.51 Q14 ~= 16678 * 64 * 2
         *   (MR67)                 K = 2065161.51 Q14 ~= 32268 * 32 * 2
         *   (MR74)                 K = 2085641.51 Q14 ~= 32588 * 32 * 2
         *   (MR795)                K = 2183945.51 Q14 ~= 17062 * 64 * 2
         *   (MR102)                K = 2134793.51 Q14 ~= 16678 * 64 * 2         
         */

        if (test (), sub (mode, MR102) == 0)
        {
            /* mean = 33 dB */
            L_tmp = L_mac(L_tmp, 16678, 64);     /* Q14 */
        }
        else if (test (), sub (mode, MR795) == 0)
        {
            /* ener_code  = <xn xn> * 2^27*2^exp_code
               frac_en    = ener_code / 2^16
                          = <xn xn> * 2^11*2^exp_code
               <xn xn>    = <xn xn>*2^11*2^exp * 2^exp_en
                         := frac_en            * 2^exp_en

               ==> exp_en = -11-exp_code;
             */
            *frac_en = extract_h (ener_code); move16 ();
            *exp_en = sub (-11, exp_code);    move16 ();

            /* mean = 36 dB */
            L_tmp = L_mac(L_tmp, 17062, 64);     /* Q14 */
        }
        else if (test (), sub (mode, MR74) == 0)
        {
            /* mean = 30 dB */
            L_tmp = L_mac(L_tmp, 32588, 32);     /* Q14 */
        }
        else if (test (), sub (mode, MR67) == 0)
        {
            /* mean = 28.75 dB */
            L_tmp = L_mac(L_tmp, 32268, 32);     /* Q14 */
        }
        else /* MR59, MR515, MR475 */
        {
            /* mean = 33 dB */
            L_tmp = L_mac(L_tmp, 16678, 64);     /* Q14 */
        }
        
        /*-----------------------------------------------------------------*
         * Compute gcode0.                                                 *
         *  = Sum(i=0,3) pred[i]*past_qua_en[i] - ener_code + mean_ener    *
         *-----------------------------------------------------------------*/

        L_tmp = L_shl(L_tmp, 10);                /* Q24 */
        for (i = 0; i < 4; i++)
            L_tmp = L_mac(L_tmp, pred[i], st->past_qua_en[i]);
                                                 /* Q13 * Q10 -> Q24 */

        gcode0 = extract_h(L_tmp);               /* Q8  */

        /*-----------------------------------------------------------------*
         * gcode0 = pow(10.0, gcode0/20)                                   *
         *        = pow(2, 3.3219*gcode0/20)                               *
         *        = pow(2, 0.166*gcode0)                                   *
         *-----------------------------------------------------------------*/

        /* 5439 Q15 = 0.165985                                        */
        /* (correct: 1/(20*log10(2)) 0.166096 = 5443 Q15)             */
        test ();
        if (sub (mode, MR74) == 0) /* For IS641 bitexactness */
            L_tmp = L_mult(gcode0, 5439);  /* Q8 * Q15 -> Q24 */
        else
            L_tmp = L_mult(gcode0, 5443);  /* Q8 * Q15 -> Q24 */

        L_tmp = L_shr(L_tmp, 8);                   /*          -> Q16 */
        L_Extract(L_tmp, exp_gcode0, frac_gcode0); /*       -> Q0.Q15 */
    }
}


/*************************************************************************
 *
 * FUNCTION:  gc_pred_update()
 *
 * PURPOSE: update MA predictor with last quantized energy
 *
 *************************************************************************/
void gc_pred_update(
    gc_predState *st,      /* i/o: State struct                     */
    Word16 qua_ener_MR122, /* i  : quantized energy for update, Q10 */
                           /*      (log2(qua_err))                  */
    Word16 qua_ener        /* i  : quantized energy for update, Q10 */
                           /*      (20*log10(qua_err))              */
)
{
    Word16 i;

    for (i = 3; i > 0; i--)
    {
        st->past_qua_en[i] = st->past_qua_en[i - 1];             move16 ();
        st->past_qua_en_MR122[i] = st->past_qua_en_MR122[i - 1]; move16 ();
    }

    st->past_qua_en_MR122[0] = qua_ener_MR122;  /*    log2 (qua_err), Q10 */
	                                                             move16 ();
    st->past_qua_en[0] = qua_ener;              /* 20*log10(qua_err), Q10 */
	                                                             move16 ();
}

/*************************************************************************
 *
 * FUNCTION:  gc_pred_average_limited()
 *
 * PURPOSE: get average of MA predictor state values (with a lower limit)
 *          [used in error concealment]
 *
 *************************************************************************/
void gc_pred_average_limited(
    gc_predState *st,       /* i: State struct                    */
    Word16 *ener_avg_MR122, /* o: everaged quantized energy,  Q10 */
                            /*    (log2(qua_err))                 */
    Word16 *ener_avg        /* o: averaged quantized energy,  Q10 */
                            /*    (20*log10(qua_err))             */
)
{
    Word16 av_pred_en;
    Word16 i;

    /* do average in MR122 mode (log2() domain) */
    av_pred_en = 0;                                        move16 ();
    for (i = 0; i < NPRED; i++)
    {
        av_pred_en = add (av_pred_en, st->past_qua_en_MR122[i]);
    }

    /* av_pred_en = 0.25*av_pred_en */
    av_pred_en = mult (av_pred_en, 8192);

    /* if (av_pred_en < -14/(20Log10(2))) av_pred_en = .. */
    test ();
    if (sub (av_pred_en, MIN_ENERGY_MR122) < 0)
    {
        av_pred_en = MIN_ENERGY_MR122;                     move16 ();
    }
    *ener_avg_MR122 = av_pred_en;                          move16 ();

    /* do average for other modes (20*log10() domain) */
    av_pred_en = 0;                                        move16 ();
    for (i = 0; i < NPRED; i++)
    {
        av_pred_en = add (av_pred_en, st->past_qua_en[i]);
    }

    /* av_pred_en = 0.25*av_pred_en */
    av_pred_en = mult (av_pred_en, 8192);

    /* if (av_pred_en < -14) av_pred_en = .. */
    test ();
    if (sub (av_pred_en, MIN_ENERGY) < 0)
    {
        av_pred_en = MIN_ENERGY;                           move16 ();
    }
    *ener_avg = av_pred_en;                                move16 ();
}