gc_pred.cpp

实现3GPP的GSM中AMR语音的CODECS。

        {
            *pOverflow = 1;
            L_tmp = MAX_32;
        }
        else if (L_tmp < (Word32) 0xffe00000L)
        {
            *pOverflow = 1;
            L_tmp = MIN_32;
        }
        else
        {
            L_tmp = L_tmp << 10;
        }

        for (i = 0; i < 4; i++)
        {
            L_temp2 = ((((Word32) pred[i]) * st->past_qua_en[i]) << 1);
            L_tmp = L_add(L_tmp, L_temp2, pOverflow);  /* Q13 * Q10 -> Q24 */
        }

        gcode0 = (Word16)(L_tmp >> 16);               /* 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)            */

        if (mode == MR74) /* For IS641 bitexactness */
        {
            L_tmp = (((Word32) gcode0) * 5439) << 1;  /* Q8 * Q15 -> Q24 */
        }
        else
        {
            L_tmp = (((Word32) gcode0) * 5443) << 1;  /* Q8 * Q15 -> Q24 */
        }

        if (L_tmp < 0)
        {
            L_tmp = ~((~L_tmp) >> 8);
        }
        else
        {
            L_tmp = L_tmp >> 8;     /* -> Q16 */
        }

        *exp_gcode0 = (Word16)(L_tmp >> 16);
        if (L_tmp < 0)
        {
            L_temp1 = ~((~L_tmp) >> 1);
        }
        else
        {
            L_temp1 = L_tmp >> 1;
        }
        L_temp2 = (Word32) * exp_gcode0 << 15;
        *frac_gcode0 = (Word16)(L_sub(L_temp1, L_temp2, pOverflow));
        /* -> Q0.Q15 */
    }

    return;
}

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

/*
------------------------------------------------------------------------------
 FUNCTION NAME: gc_pred_update
------------------------------------------------------------------------------
 INPUT AND OUTPUT DEFINITIONS

 Inputs:
    st = pointer to a structure of type gc_predState
    qua_ener_MR122 = quantized energy for update (Q10); calculated as
             (log2(qua_err)) (Word16)
    qua_ener = quantized energy for update (Q10); calculated as
           (20*log10(qua_err)) (Word16)

 Outputs:
    structure pointed to by st contains the calculated quantized energy
      for update

 Returns:
    None

 Global Variables Used:
    None

 Local Variables Needed:
    None

------------------------------------------------------------------------------
 FUNCTION DESCRIPTION

 This function updates the MA predictor with the last quantized energy.

------------------------------------------------------------------------------
 REQUIREMENTS

 None

------------------------------------------------------------------------------
 REFERENCES

 gc_pred.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001

------------------------------------------------------------------------------
 PSEUDO-CODE

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];
        st->past_qua_en_MR122[i] = st->past_qua_en_MR122[i - 1];
    }

    st->past_qua_en_MR122[0] = qua_ener_MR122;  //    log2 (qua_err), Q10

    st->past_qua_en[0] = qua_ener;              // 20*log10(qua_err), Q10

}

------------------------------------------------------------------------------
 RESOURCES USED [optional]

 When the code is written for a specific target processor the
 the resources used should be documented below.

 HEAP MEMORY USED: x bytes

 STACK MEMORY USED: x bytes

 CLOCK CYCLES: (cycle count equation for this function) + (variable
                used to represent cycle count for each subroutine
                called)
     where: (cycle count variable) = cycle count for [subroutine
                                     name]

------------------------------------------------------------------------------
 CAUTION [optional]
 [State any special notes, constraints or cautions for users of this function]

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

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))              */
)
{
    st->past_qua_en[3] = st->past_qua_en[2];
    st->past_qua_en_MR122[3] = st->past_qua_en_MR122[2];

    st->past_qua_en[2] = st->past_qua_en[1];
    st->past_qua_en_MR122[2] = st->past_qua_en_MR122[1];

    st->past_qua_en[1] = st->past_qua_en[0];
    st->past_qua_en_MR122[1] = st->past_qua_en_MR122[0];

    st->past_qua_en_MR122[0] = qua_ener_MR122; /*    log2 (qua_err), Q10 */

    st->past_qua_en[0] = qua_ener;            /* 20*log10(qua_err), Q10 */

    return;
}

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

/*
------------------------------------------------------------------------------
 FUNCTION NAME: gc_pred_average_limited
------------------------------------------------------------------------------
 INPUT AND OUTPUT DEFINITIONS

 Inputs:
    st = pointer to a structure of type gc_predState
    ener_avg_MR122 = pointer to the averaged quantized energy (Q10);
             calculated as (log2(qua_err)) (Word16)
    ener_avg = pointer to the averaged quantized energy (Q10); calculated
           as (20*log10(qua_err)) (Word16)
    pOverflow = pointer to overflow (Flag)

 Outputs:
    store pointed to by ener_avg_MR122 contains the new averaged quantized
      energy
    store pointed to by ener_avg contains the new averaged quantized
      energy
    pOverflow = 1 if the math functions called by gc_pred_average_limited
            results in overflow else zero.

 Returns:
    None

 Global Variables Used:
    None

 Local Variables Needed:
    None

------------------------------------------------------------------------------
 FUNCTION DESCRIPTION

 This function calculates the average of MA predictor state values (with a
 lower limit) used in error concealment.

------------------------------------------------------------------------------
 REQUIREMENTS

 None

------------------------------------------------------------------------------
 REFERENCES

 gc_pred.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001

------------------------------------------------------------------------------
 PSEUDO-CODE

The original etsi reference code uses a global flag Overflow. However, in the
actual implementation a pointer to a the overflow flag is passed in.

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;
    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 = ..

    if (sub (av_pred_en, MIN_ENERGY_MR122) < 0)
    {
        av_pred_en = MIN_ENERGY_MR122;
    }
    *ener_avg_MR122 = av_pred_en;

    // do average for other modes (20*log10() domain)
    av_pred_en = 0;
    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 = ..

    if (sub (av_pred_en, MIN_ENERGY) < 0)
    {
        av_pred_en = MIN_ENERGY;
    }
    *ener_avg = av_pred_en;
}

------------------------------------------------------------------------------
 RESOURCES USED [optional]

 When the code is written for a specific target processor the
 the resources used should be documented below.

 HEAP MEMORY USED: x bytes

 STACK MEMORY USED: x bytes

 CLOCK CYCLES: (cycle count equation for this function) + (variable
                used to represent cycle count for each subroutine
                called)
     where: (cycle count variable) = cycle count for [subroutine
                                     name]

------------------------------------------------------------------------------
 CAUTION [optional]
 [State any special notes, constraints or cautions for users of this function]

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

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))             */
    Flag *pOverflow
)
{
    Word16 av_pred_en;
    register Word16 i;

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

    /* av_pred_en = 0.25*av_pred_en  (with sign-extension)*/
    if (av_pred_en < 0)
    {
        av_pred_en = (av_pred_en >> 2) | 0xc000;
    }
    else
    {
        av_pred_en >>= 2;
    }

    /* if (av_pred_en < -14/(20Log10(2))) av_pred_en = .. */
    if (av_pred_en < MIN_ENERGY_MR122)
    {
        av_pred_en = MIN_ENERGY_MR122;
    }
    *ener_avg_MR122 = av_pred_en;

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

    /* av_pred_en = 0.25*av_pred_en  (with sign-extension)*/
    if (av_pred_en < 0)
    {
        av_pred_en = (av_pred_en >> 2) | 0xc000;
    }
    else
    {
        av_pred_en >>= 2;
    }

    /* if (av_pred_en < -14) av_pred_en = .. */
    if (av_pred_en < MIN_ENERGY)
    {
        av_pred_en = MIN_ENERGY;
    }
    *ener_avg = av_pred_en;
}