int_lpc.cpp

实现3GPP的GSM中AMR语音的CODECS。

                             present frame (M)                               */
    Word16 Az[],       /* o :interpolated LP parameters
                             in subframes 1 and 3 (AZ_SIZE)                  */
    Flag  *pOverflow
)
{
    Word16 i;
    Word16 lsp[M];
    Word16 *p_lsp_old = &lsp_old[0];
    Word16 *p_lsp_mid = &lsp_mid[0];
    Word16 *p_lsp_new = &lsp_new[0];
    Word16 *p_lsp     = &lsp[0];

    /*  lsp[i] = lsp_mid[i] * 0.5 + lsp_old[i] * 0.5 */

    for (i = M >> 1; i != 0; i--)
    {
        *(p_lsp++) = (*(p_lsp_old++) >> 1) + (*(p_lsp_mid++) >> 1);
        *(p_lsp++) = (*(p_lsp_old++) >> 1) + (*(p_lsp_mid++) >> 1);
    }
    Lsp_Az(lsp, Az, pOverflow);            /* Subframe 1 */
    Az += MP1 * 2;

    p_lsp_mid = &lsp_mid[0];
    p_lsp     = &lsp[0];

    for (i = M >> 1; i != 0; i--)
    {
        *(p_lsp++) = (*(p_lsp_mid++) >> 1) + (*(p_lsp_new++) >> 1);
        *(p_lsp++) = (*(p_lsp_mid++) >> 1) + (*(p_lsp_new++) >> 1);
    }

    Lsp_Az(lsp, Az, pOverflow);            /* Subframe 3 */

    return;
}


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

 Inputs:
    lsp_old -- array of type Word16 -- LSP vector at the
                                       4th subfr. of past frame (M)
    lsp_new -- array of type Word16 -- LSP vector at the 4th subfr. of
                                       present frame (M)

 Outputs:
    Az -- array of type Word16 -- interpolated LP parameters in.
                                  all subframes.
    pOverflow -- pointer to type Flag -- Overflow indicator

 Returns:
    None

 Global Variables Used:


 Local Variables Needed:
    None

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

 PURPOSE:  Interpolates the LSPs and convert to LP parameters to get
           a different LP filter in each subframe.

 DESCRIPTION:
    The 20 ms speech frame is divided into 4 subframes.
    The LSPs are quantized and transmitted at the 4th subframe
    (once per frame) and interpolated at the 1st, 2nd and 3rd subframe.

         |------|------|------|------|
            sf1    sf2    sf3    sf4
      F0                          F1

    sf1:   3/4 F0 + 1/4 F1         sf3:   1/4 F0 + 3/4 F1
    sf2:   1/2 F0 + 1/2 F1         sf4:       F1

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

 None

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

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

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


------------------------------------------------------------------------------
 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 Int_lpc_1to3(
    Word16 lsp_old[], /* input : LSP vector at the 4th SF of past frame    */
    Word16 lsp_new[], /* input : LSP vector at the 4th SF of present frame */
    Word16 Az[],      /* output: interpolated LP parameters in all SFs     */
    Flag   *pOverflow
)
{
    Word16 i;
    Word16 temp;
    Word16 temp2;

    Word16 lsp[M];

    for (i = 0; i < M; i++)
    {
        temp = shr(lsp_old[i], 2, pOverflow);
        temp = sub(lsp_old[i], temp, pOverflow);
        temp2 = shr(lsp_new[i], 2, pOverflow);

        lsp[i] = add(temp2, temp, pOverflow);
    }

    Lsp_Az(
        lsp,
        Az,
        pOverflow);        /* Subframe 1 */

    Az += MP1;


    for (i = 0; i < M; i++)
    {
        temp = shr(lsp_new[i], 1, pOverflow);
        temp2 = shr(lsp_old[i], 1, pOverflow);
        lsp[i] = add(temp, temp2, pOverflow);
    }

    Lsp_Az(
        lsp,
        Az,
        pOverflow);        /* Subframe 2 */

    Az += MP1;

    for (i = 0; i < M; i++)
    {
        temp = shr(lsp_new[i], 2, pOverflow);
        temp = sub(lsp_new[i], temp, pOverflow);
        temp2 = shr(lsp_old[i], 2, pOverflow);

        lsp[i] = add(temp2, temp, pOverflow);
    }

    Lsp_Az(
        lsp,
        Az,
        pOverflow);       /* Subframe 3 */

    Az += MP1;

    Lsp_Az(
        lsp_new,
        Az,
        pOverflow);        /* Subframe 4 */

    return;
}
/*
------------------------------------------------------------------------------
 FUNCTION NAME: Int_lpc_1to3_2
------------------------------------------------------------------------------
 INPUT AND OUTPUT DEFINITIONS

 Inputs:
    lsp_old -- array of type Word16 -- LSP vector at the
                                       4th subfr. of past frame (M)
    lsp_new -- array of type Word16 -- LSP vector at the 4th subfr. of
                                       present frame (M)

 Outputs:
    Az -- array of type Word16 -- interpolated LP parameters in.
                                  subfr 1, 2, and 3.
    pOverflow -- pointer to type Flag -- Overflow indicator

 Returns:
    None

 Global Variables Used:
    None

 Local Variables Needed:
    None

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

 Interpolation of the LPC parameters.
 Same as the previous function but we do not recompute Az() for
 subframe 4 because it is already available.

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

 None

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

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

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


------------------------------------------------------------------------------
 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 Int_lpc_1to3_2(
    Word16 lsp_old[],  /* input : LSP vector at the 4th SF of past frame    */
    Word16 lsp_new[],  /* input : LSP vector at the 4th SF of present frame */
    Word16 Az[],       /* output: interpolated LP parameters in SFs 1,2,3   */
    Flag   *pOverflow
)
{
    Word16 i;
    Word16 temp;
    Word16 temp2;
    Word16 lsp[M];

    for (i = 0; i < M; i++)
    {
        temp = shr(lsp_old[i], 2, pOverflow);

        temp = sub(lsp_old[i], temp, pOverflow);

        temp2 = shr(lsp_new[i], 2, pOverflow);

        lsp[i] = add(temp2, temp, pOverflow);
    }

    Lsp_Az(
        lsp,
        Az,
        pOverflow);        /* Subframe 1 */

    Az += MP1;

    for (i = 0; i < M; i++)
    {
        temp = shr(lsp_new[i], 1, pOverflow);
        temp2 = shr(lsp_old[i], 1, pOverflow);

        lsp[i] = add(temp2, temp, pOverflow);
    }

    Lsp_Az(
        lsp,
        Az,
        pOverflow);        /* Subframe 2 */

    Az += MP1;

    for (i = 0; i < M; i++)
    {
        temp = shr(lsp_new[i], 2, pOverflow);
        temp = sub(lsp_new[i], temp, pOverflow);
        temp2 = shr(lsp_old[i], 2, pOverflow);

        lsp[i] = add(temp, temp2, pOverflow);
    }

    Lsp_Az(
        lsp,
        Az,
        pOverflow);        /* Subframe 3 */

    return;
}