pre_proc.cpp

实现3GPP的GSM中AMR语音的CODECS。

------------------------------------------------------------------------------
 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]

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

Word16 Pre_Process_reset(Pre_ProcessState *state)
{
    if (state == (Pre_ProcessState *) NULL)
    {
        /*  fprintf(stderr, "Pre_Process_reset: invalid parameter\n");  */
        return(-1);
    }

    state->y2_hi = 0;
    state->y2_lo = 0;
    state->y1_hi = 0;
    state->y1_lo = 0;
    state->x0 = 0;
    state->x1 = 0;

    return(0);
}

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


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

 Inputs:
    state = a pointer to an array of pointers to structures of
        type Pre_ProcessState

 Outputs:
    state points to a NULL address

 Returns:
    None.

 Global Variables Used:
    None.

 Local Variables Needed:
    None.

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

 The memory used for state memory is freed.

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

 None.

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

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

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

void Pre_Process_exit (Pre_ProcessState **state)
{
  if (state == NULL || *state == NULL)
      return;

  // deallocate memory
  free(*state);
  *state = NULL;

  return;
}

------------------------------------------------------------------------------
 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 Pre_Process_exit(Pre_ProcessState **state)
{
    if (state == NULL || *state == NULL)
    {
        return;
    }

    /* deallocate memory */
    oscl_free(*state);
    *state = NULL;

    return;
}

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

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

 Inputs:
    st = a pointer to a structure of type Pre_ProcessState
    signal = input/output signal (Word16)
    lg = length of signal (Word16)

 Outputs:
    st points to the updated structure

 Returns:
    return_value = 0 (int)

 Global Variables Used:
    a = points to a buffer of filter coefficients
    b = points to a buffer of filter coefficients

 Local Variables Needed:
    None.

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

 This module performs the preprocessing of the input speech.
 The signal is passed through a 2nd order high pass filtering with cut off
 frequency at 80 Hz. The input is divided by two in the filtering process.

    y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b[2]*x[i-2]/2
                     + a[1]*y[i-1] + a[2]*y[i-2];

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

 None.

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

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

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

int Pre_Process (
    Pre_ProcessState *st,
    Word16 signal[], // input/output signal
    Word16 lg)       // lenght of signal
{
    Word16 i, x2;
    Word32 L_tmp;

    for (i = 0; i < lg; i++)
    {
        x2 = st->x1;
        st->x1 = st->x0;
        st->x0 = signal[i];

        //  y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b140[2]*x[i-2]/2
        //                     + a[1]*y[i-1] + a[2] * y[i-2];

        L_tmp = Mpy_32_16 (st->y1_hi, st->y1_lo, a[1]);
        L_tmp = L_add (L_tmp, Mpy_32_16 (st->y2_hi, st->y2_lo, a[2]));
        L_tmp = L_mac (L_tmp, st->x0, b[0]);
        L_tmp = L_mac (L_tmp, st->x1, b[1]);
        L_tmp = L_mac (L_tmp, x2, b[2]);
        L_tmp = L_shl (L_tmp, 3);
        signal[i] = pv_round (L_tmp);

        st->y2_hi = st->y1_hi;
        st->y2_lo = st->y1_lo;
        L_Extract (L_tmp, &st->y1_hi, &st->y1_lo);
    }
    return 0;
}

------------------------------------------------------------------------------
 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]

------------------------------------------------------------------------------
*/
/*
    filter coefficients (fc = 80 Hz, coeff. b[] is divided by 2)
    const Word16 b[3] = {1899, -3798, 1899};
    const Word16 a[3] = {4096, 7807, -3733};

*/

void Pre_Process(
    Pre_ProcessState *st,
    Word16 signal[], /* input/output signal */
    Word16 lg)       /* length of signal    */
{
    register Word16 i;
    Word16 x_n_2;
    Word16 x_n_1;
    Word32 L_tmp;
    Word16 *p_signal = signal;

    x_n_2 = st->x1;
    x_n_1 = st->x0;

    for (i = lg; i != 0; i--)
    {


        /*  y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b140[2]*x[i-2]/2  */
        /*                     + a[1]*y[i-1] + a[2] * y[i-2];      */

        L_tmp     = ((Word32) st->y1_hi) * 7807;
        L_tmp    += (Word32)(((Word32) st->y1_lo * 7807) >> 15);

        L_tmp    += ((Word32) st->y2_hi) * (-3733);
        st->y2_hi =  st->y1_hi;
        L_tmp    += (Word32)(((Word32) st->y2_lo * (-3733)) >> 15);
        st->y2_lo =  st->y1_lo;

        L_tmp    += ((Word32) x_n_2) * 1899;
        x_n_2     =  x_n_1;
        L_tmp    += ((Word32) x_n_1) * (-3798);
        x_n_1     = *(p_signal);
        L_tmp    += ((Word32) x_n_1) * 1899;


        *(p_signal++) = (Word16)((L_tmp + 0x0000800L) >> 12);

        st->y1_hi = (Word16)(L_tmp >> 12);
        st->y1_lo = (Word16)((L_tmp << 3) - ((Word32)(st->y1_hi) << 15));

    }

    st->x1 = x_n_2;
    st->x0 = x_n_1;

    return;
}