/***************************************************************************
 *
 *   File Name: dtx.c
 *
 *   Purpose:   Contains functions for performing DTX operation and comfort
 *              noise generation.
 *
 *     Below is a listing of all the functions appearing in the file.
 *     The functions are arranged according to their purpose.  Under
 *     each heading, the ordering is hierarchical.
 *
 *     Resetting of static variables of TX DTX:
 *       reset_tx_dtx()
 *     Resetting of static variables of RX DTX:
 *       reset_rx_dtx()
 *
 *     TX DTX handler (called by the speech encoder):
 *       tx_dtx()
 *     RX DTX handler (called by the speech decoder):
 *       rx_dtx()
 *     Encoding of comfort noise parameters into SID frame:
 *       CN_encoding()
 *     Encoding of SID codeword into SID frame:
 *       sid_codeword_encoding()
 *     Detecting of SID codeword from a frame:
 *       sid_frame_detection()
 *     Update the LSF parameter history:
 *       update_lsf_history()
 *     Update the reference LSF parameter vector:
 *       update_lsf_p_CN()
 *     Compute the averaged LSF parameter vector:
 *       aver_lsf_history()
 *     Update the fixed codebook gain parameter history of the encoder:
 *       update_gain_code_history_tx()
 *     Update the fixed codebook gain parameter history of the decoder:
 *       update_gain_code_history_rx()
 *     Compute the unquantized fixed codebook gain:
 *       compute_CN_excitation_gain()
 *     Update the reference fixed codebook gain:
 *       update_gcode0_CN()
 *     Compute the averaged fixed codebook gain:
 *       aver_gain_code_history()
 *     Compute the comfort noise fixed codebook excitation:
 *       build_CN_code()
 *       Generate a random integer value:
 *         pseudonoise()
 *     Interpolate a comfort noise parameter value over the comfort noise
 *       update period:
 *       interpolate_CN_param()
 *     Interpolate comfort noise LSF pparameter values over the comfort
 *       noise update period:
 *       interpolate_CN_lsf()
 *         interpolate_CN_param()
 *
 **************************************************************************/

#include "gsm_efr.h"
#include "typedef.h"
#include "namespace.h"
#include "basic_op.h"
#include "cnst.h"
#include "sig_proc.h"
#include "memops.h"
#include "no_count.h"
#include "dtx.h"
#include "enc_state.h"
#include "dec_state.h"

/* Inverse values of DTX hangover period and DTX hangover period + 1 */

#define INV_DTX_HANGOVER (0x7fff / DTX_HANGOVER)
#define INV_DTX_HANGOVER_P1 (0x7fff / (DTX_HANGOVER+1))

#define NB_PULSE 10 /* Number of pulses in fixed codebook excitation */

/* Constant DTX_ELAPSED_THRESHOLD is used as threshold for allowing
   SID frame updating without hangover period in case when elapsed
   time measured from previous SID update is below 24 */

#define DTX_ELAPSED_THRESHOLD (24 + DTX_HANGOVER - 1)

/*************************************************************************
 *
 *   FUNCTION NAME: reset_tx_dtx
 *
 *   PURPOSE:  Resets the static variables of the TX DTX handler to their
 *             initial values
 *
 *************************************************************************/

void reset_tx_dtx (struct EFR_encoder_state *st)
{
    Word16 i;

    /* suppose infinitely long speech period before start */

    st->txdtx_hangover = DTX_HANGOVER;
    st->txdtx_N_elapsed = 0x7fff;
    st->txdtx_ctrl = TX_SP_FLAG | TX_VAD_FLAG;

    for (i = 0; i < 6; i++)
    {
        st->old_CN_mem_tx[i] = 0;
    }

    for (i = 0; i < DTX_HANGOVER; i++)
    {
        st->lsf_old_tx[i][0] = 1384;
        st->lsf_old_tx[i][1] = 2077;
        st->lsf_old_tx[i][2] = 3420;
        st->lsf_old_tx[i][3] = 5108;
        st->lsf_old_tx[i][4] = 6742;
        st->lsf_old_tx[i][5] = 8122;
        st->lsf_old_tx[i][6] = 9863;
        st->lsf_old_tx[i][7] = 11092;
        st->lsf_old_tx[i][8] = 12714;
        st->lsf_old_tx[i][9] = 13701;
    }

    for (i = 0; i < 4 * DTX_HANGOVER; i++)
    {
        st->gain_code_old_tx[i] = 0;
    }

    st->L_pn_seed_tx = PN_INITIAL_SEED;

    st->buf_p_tx = 0;
    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: reset_rx_dtx
 *
 *   PURPOSE:  Resets the static variables of the RX DTX handler to their
 *             initial values
 *
 *************************************************************************/

void reset_rx_dtx (struct EFR_decoder_state *st)
{
    Word16 i;

    /* suppose infinitely long speech period before start */

    st->rxdtx_aver_period = DTX_HANGOVER;
    st->rxdtx_N_elapsed = 0x7fff;
    st->rxdtx_ctrl = RX_SP_FLAG;

    for (i = 0; i < DTX_HANGOVER; i++)
    {
        st->lsf_old_rx[i][0] = 1384;
        st->lsf_old_rx[i][1] = 2077;
        st->lsf_old_rx[i][2] = 3420;
        st->lsf_old_rx[i][3] = 5108;
        st->lsf_old_rx[i][4] = 6742;
        st->lsf_old_rx[i][5] = 8122;
        st->lsf_old_rx[i][6] = 9863;
        st->lsf_old_rx[i][7] = 11092;
        st->lsf_old_rx[i][8] = 12714;
        st->lsf_old_rx[i][9] = 13701;
    }

    for (i = 0; i < 4 * DTX_HANGOVER; i++)
    {
        st->gain_code_old_rx[i] = 0;
    }

    st->L_pn_seed_rx = PN_INITIAL_SEED;
    st->rx_dtx_state = CN_INT_PERIOD - 1;

    st->prev_SID_frames_lost = 0;
    st->buf_p_rx = 0;

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: tx_dtx
 *
 *   PURPOSE: DTX handler of the speech encoder. Determines when to add
 *            the hangover period to the end of the speech burst, and
 *            also determines when to use old SID parameters, and when
 *            to update the SID parameters. This function also initializes
 *            the pseudo noise generator shift register.
 *
 *            Operation of the TX DTX handler is based on the VAD flag
 *            given as input from the speech encoder.
 *
 *   INPUTS:      VAD_flag      Voice activity decision
 *                *txdtx_ctrl   Old encoder DTX control word
 *
 *   OUTPUTS:     *txdtx_ctrl   Updated encoder DTX control word
 *                L_pn_seed_tx  Initialized pseudo noise generator shift
 *                              register (global variable)
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void tx_dtx (
    struct EFR_encoder_state *st,
    Word16 VAD_flag
)
{
    /* N_elapsed (frames since last SID update) is incremented. If SID
       is updated N_elapsed is cleared later in this function */

    st->txdtx_N_elapsed = add (st->txdtx_N_elapsed, 1);

    /* If voice activity was detected, reset hangover counter */

    if (sub (VAD_flag, 1) == 0)
    {
        st->txdtx_hangover = DTX_HANGOVER;
        st->txdtx_ctrl = TX_SP_FLAG | TX_VAD_FLAG;
    }
    else
    {
        if (st->txdtx_hangover == 0)
        {
            /* Hangover period is over, SID should be updated */

            st->txdtx_N_elapsed = 0;

            /* Check if this is the first frame after hangover period */
            if ((st->txdtx_ctrl & TX_HANGOVER_ACTIVE) != 0)
            {
                st->txdtx_ctrl = TX_PREV_HANGOVER_ACTIVE
                    | TX_SID_UPDATE;
                st->L_pn_seed_tx = PN_INITIAL_SEED;
            }
            else
            {
                st->txdtx_ctrl = TX_SID_UPDATE;
            }
        }
        else
        {
            /* Hangover period is not over, update hangover counter */
            st->txdtx_hangover = sub (st->txdtx_hangover, 1);

            /* Check if elapsed time from last SID update is greater than
               threshold. If not, set SP=0 (although hangover period is not
               over) and use old SID parameters for new SID frame.
               N_elapsed counter must be summed with hangover counter in order
               to avoid erroneus SP=1 decision in case when N_elapsed is grown
               bigger than threshold and hangover period is still active */

            if (sub (add (st->txdtx_N_elapsed, st->txdtx_hangover),
                     DTX_ELAPSED_THRESHOLD) < 0)
            {
                /* old SID frame should be used */
                st->txdtx_ctrl = TX_USE_OLD_SID;
            }
            else
            {
                if ((st->txdtx_ctrl & TX_HANGOVER_ACTIVE) != 0)
                {
                    st->txdtx_ctrl = TX_PREV_HANGOVER_ACTIVE
                        | TX_HANGOVER_ACTIVE
                        | TX_SP_FLAG;
                }
                else
                {
                    st->txdtx_ctrl = TX_HANGOVER_ACTIVE
                        | TX_SP_FLAG;
                }
            }
        }
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: rx_dtx
 *
 *   PURPOSE: DTX handler of the speech decoder. Determines when to update
 *            the reference comfort noise parameters (LSF and gain) at the
 *            end of the speech burst. Also classifies the incoming frames
 *            according to SID flag and BFI flag
 *            and determines when the transmission is active during comfort
 *            noise insertion. This function also initializes the pseudo
 *            noise generator shift register.
 *
 *            Operation of the RX DTX handler is based on measuring the
 *            lengths of speech bursts and the lengths of the pauses between
 *            speech bursts to determine when there exists a hangover period
 *            at the end of a speech burst. The idea is to keep in sync with
 *            the TX DTX handler to be able to update the reference comfort
 *            noise parameters at the same time instances.
 *
 *   INPUTS:      *rxdtx_ctrl   Old decoder DTX control word
 *                TAF           Time alignment flag
 *                bfi           Bad frame indicator flag
 *                SID_flag      Silence descriptor flag
 *
 *   OUTPUTS:     *rxdtx_ctrl   Updated decoder DTX control word
 *                rx_dtx_state  Updated state of comfort noise interpolation
 *                              period (global variable)
 *                L_pn_seed_rx  Initialized pseudo noise generator shift
 *                              register (global variable)
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void rx_dtx (
    struct EFR_decoder_state *st,
    Word16 TAF,
    Word16 bfi,
    Word16 SID_flag
)
{
    Word16 frame_type;

    /* Frame classification according to bfi-flag and ternary-valued
       SID flag. The frames between SID updates (not actually trans-
       mitted) are also classified here; they will be discarded later
       and provided with "NO TRANSMISSION"-flag */

    if ((sub (SID_flag, 2) == 0) && (bfi == 0))
    {
        frame_type = VALID_SID_FRAME;                   move16 (); 
    }
    else if ((SID_flag == 0) && (bfi == 0))
    {
        frame_type = GOOD_SPEECH_FRAME;                 move16 (); 
    }
    else if ((SID_flag == 0) && (bfi != 0))
    {
        frame_type = UNUSABLE_FRAME;                    move16 (); 
    }
    else
    {
        frame_type = INVALID_SID_FRAME;                 move16 (); 
    }

    /* Update of decoder state */
    /* Previous frame was classified as a speech frame */
    if ((st->rxdtx_ctrl & RX_SP_FLAG) != 0)
    {
        if (sub (frame_type, VALID_SID_FRAME) == 0)
        {
            st->rxdtx_ctrl = RX_FIRST_SID_UPDATE;
        }
        else if (sub (frame_type, INVALID_SID_FRAME) == 0)
        {
            st->rxdtx_ctrl = RX_FIRST_SID_UPDATE
                           | RX_INVALID_SID_FRAME;
        }
        else if (sub (frame_type, UNUSABLE_FRAME) == 0)
        {
            st->rxdtx_ctrl = RX_SP_FLAG;
        }
        else if (sub (frame_type, GOOD_SPEECH_FRAME) == 0)
        {
            st->rxdtx_ctrl = RX_SP_FLAG;
        }
    }
    else
    {
        if (sub (frame_type, VALID_SID_FRAME) == 0)
        {
            st->rxdtx_ctrl = RX_CONT_SID_UPDATE;
        }
        else if (sub (frame_type, INVALID_SID_FRAME) == 0)
        {
            st->rxdtx_ctrl = RX_CONT_SID_UPDATE
                           | RX_INVALID_SID_FRAME;
        }
        else if (sub (frame_type, UNUSABLE_FRAME) == 0)
        {
            st->rxdtx_ctrl = RX_CNI_BFI;
        }
        else if (sub (frame_type, GOOD_SPEECH_FRAME) == 0)
        {
            /* If the previous frame (during CNI period) was muted,
               raise the RX_PREV_DTX_MUTING flag */
            if ((st->rxdtx_ctrl & RX_DTX_MUTING) != 0)
            {
                st->rxdtx_ctrl = RX_SP_FLAG | RX_FIRST_SP_FLAG
                               | RX_PREV_DTX_MUTING;
            }
            else
            {
                st->rxdtx_ctrl = RX_SP_FLAG | RX_FIRST_SP_FLAG;
            }
        }
    }

    if ((st->rxdtx_ctrl & RX_SP_FLAG) != 0)
    {
        st->prev_SID_frames_lost = 0;
        st->rx_dtx_state = CN_INT_PERIOD - 1;
    }
    else
    {
        /* First SID frame */
        if ((st->rxdtx_ctrl & RX_FIRST_SID_UPDATE) != 0)
        {
            st->prev_SID_frames_lost = 0;
            st->rx_dtx_state = CN_INT_PERIOD - 1;
        }

        /* SID frame detected, but not the first SID */
        if ((st->rxdtx_ctrl & RX_CONT_SID_UPDATE) != 0)
        {
            st->prev_SID_frames_lost = 0;

            if (sub (frame_type, VALID_SID_FRAME) == 0)
            {
                st->rx_dtx_state = 0;
            }
            else if (sub (frame_type, INVALID_SID_FRAME) == 0)
            {
                if (sub(st->rx_dtx_state, (CN_INT_PERIOD - 1)) < 0)
                {
                    st->rx_dtx_state = add(st->rx_dtx_state, 1);
                }
            }
        }

        /* Bad frame received in CNI mode */
        if ((st->rxdtx_ctrl & RX_CNI_BFI) != 0)
        {
            if (sub (st->rx_dtx_state, (CN_INT_PERIOD - 1)) < 0)
            {
                st->rx_dtx_state = add (st->rx_dtx_state, 1);
            }

            /* If an unusable frame is received during CNI period
               when TAF == 1, the frame is classified as a lost
               SID frame */
            if (sub (TAF, 1) == 0)
            {
                st->rxdtx_ctrl = st->rxdtx_ctrl | RX_LOST_SID_FRAME;
                st->prev_SID_frames_lost = add (st->prev_SID_frames_lost, 1);
            }
            else /* No transmission occurred */
            {
                st->rxdtx_ctrl = st->rxdtx_ctrl | RX_NO_TRANSMISSION;
            }

            if (sub (st->prev_SID_frames_lost, 1) > 0)
            {
                st->rxdtx_ctrl = st->rxdtx_ctrl | RX_DTX_MUTING;
            }
        }
    }

    /* N_elapsed (frames since last SID update) is incremented. If SID
       is updated N_elapsed is cleared later in this function */

    st->rxdtx_N_elapsed = add (st->rxdtx_N_elapsed, 1);

    if ((st->rxdtx_ctrl & RX_SP_FLAG) != 0)
    {
        st->rxdtx_aver_period = DTX_HANGOVER;
    }
    else
    {
        if (sub (st->rxdtx_N_elapsed, DTX_ELAPSED_THRESHOLD) > 0)
        {
            st->rxdtx_ctrl |= RX_UPD_SID_QUANT_MEM;
            st->rxdtx_N_elapsed = 0;
            st->rxdtx_aver_period = 0;
            st->L_pn_seed_rx = PN_INITIAL_SEED;
        }
        else if (st->rxdtx_aver_period == 0)
        {
            st->rxdtx_N_elapsed = 0;
        }
        else
        {
            st->rxdtx_aver_period = sub (st->rxdtx_aver_period, 1);
        }
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: CN_encoding
 *
 *   PURPOSE:  Encoding of the comfort noise parameters into a SID frame.
 *             Use old SID parameters if necessary. Set the parameter
 *             indices not used by comfort noise parameters to zero.
 *
 *   INPUTS:      params[0..56]  Comfort noise parameter frame from the
 *                               speech encoder
 *                txdtx_ctrl     TX DTX handler control word
 *
 *   OUTPUTS:     params[0..56]  Comfort noise encoded parameter frame
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void CN_encoding (
    struct EFR_encoder_state *st,
    Word16 params[],
    Word16 txdtx_ctrl
)
{
    Word16 i;

    if ((txdtx_ctrl & TX_SID_UPDATE) != 0)
    {
        /* Store new CN parameters in memory to be used later as old
           CN parameters */

        /* LPC parameter indices */
        for (i = 0; i < 5; i++)
        {
            st->old_CN_mem_tx[i] = params[i];
        }
        /* Codebook index computed in last subframe */
        st->old_CN_mem_tx[5] = params[56];
    }
    if ((txdtx_ctrl & TX_USE_OLD_SID) != 0)
    {
        /* Use old CN parameters previously stored in memory */
        for (i = 0; i < 5; i++)
        {
            params[i] = st->old_CN_mem_tx[i];
        }
        params[17] = st->old_CN_mem_tx[5];
        params[30] = st->old_CN_mem_tx[5];
        params[43] = st->old_CN_mem_tx[5];
        params[56] = st->old_CN_mem_tx[5];
    }
    /* Set all the rest of the parameters to zero (SID codeword will
       be written later) */
    for (i = 0; i < 12; i++)
    {
        params[i + 5] = 0;
        params[i + 18] = 0;
        params[i + 31] = 0;
        params[i + 44] = 0;
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: update_lsf_history
 *
 *   PURPOSE: Update the LSF parameter history. The LSF parameters kept
 *            in the buffer are used later for computing the reference
 *            LSF parameter vector and the averaged LSF parameter vector.
 *
 *   INPUTS:      lsf1[0..9]    LSF vector of the 1st half of the frame
 *                lsf2[0..9]    LSF vector of the 2nd half of the frame
 *                lsf_old[0..DTX_HANGOVER-1][0..M-1]
 *                              Old LSF history
 *
 *   OUTPUTS:     lsf_old[0..DTX_HANGOVER-1][0..M-1]
 *                              Updated LSF history
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void update_lsf_history (
    Word16 lsf1[M],
    Word16 lsf2[M],
    Word16 lsf_old[DTX_HANGOVER][M]
)
{
    Word16 i, j, temp;

    /* shift LSF data to make room for LSFs from current frame */
    /* This can also be implemented by using circular buffering */

    for (i = DTX_HANGOVER - 1; i > 0; i--)
    {
        for (j = 0; j < M; j++)
        {
            lsf_old[i][j] = lsf_old[i - 1][j];         move16 (); 
        }
    }

    /* Store new LSF data to lsf_old buffer */

    for (i = 0; i < M; i++)
    {
        temp = add (shr (lsf1[i], 1), shr (lsf2[i], 1));
        lsf_old[0][i] = temp;                          move16 (); 
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: update_lsf_p_CN
 *
 *   PURPOSE: Update the reference LSF parameter vector. The reference
 *            vector is computed by averaging the quantized LSF parameter
 *            vectors which exist in the LSF parameter history.
 *
 *   INPUTS:      lsf_old[0..DTX_HANGOVER-1][0..M-1]
 *                                 LSF parameter history
 *
 *   OUTPUTS:     lsf_p_CN[0..9]   Computed reference LSF parameter vector
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void update_lsf_p_CN (
    Word16 lsf_old[DTX_HANGOVER][M],
    Word16 lsf_p_CN[M]
)
{
    Word16 i, j;
    Word32 L_temp;

    for (j = 0; j < M; j++)
    {
        L_temp = L_mult (INV_DTX_HANGOVER, lsf_old[0][j]);
        for (i = 1; i < DTX_HANGOVER; i++)
        {
            L_temp = L_mac (L_temp, INV_DTX_HANGOVER, lsf_old[i][j]);
        }
        lsf_p_CN[j] = round (L_temp);                  move16 (); 
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: aver_lsf_history
 *
 *   PURPOSE: Compute the averaged LSF parameter vector. Computation is
 *            performed by averaging the LSF parameter vectors which exist
 *            in the LSF parameter history, together with the LSF
 *            parameter vectors of the current frame.
 *
 *   INPUTS:      lsf_old[0..DTX_HANGOVER-1][0..M-1]
 *                                   LSF parameter history
 *                lsf1[0..M-1]       LSF vector of the 1st half of the frame
 *                lsf2[0..M-1]       LSF vector of the 2nd half of the frame
 *
 *   OUTPUTS:     lsf_aver[0..M-1]   Averaged LSF parameter vector
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void aver_lsf_history (
    Word16 lsf_old[DTX_HANGOVER][M],
    Word16 lsf1[M],
    Word16 lsf2[M],
    Word16 lsf_aver[M]
)
{
    Word16 i, j;
    Word32 L_temp;

    for (j = 0; j < M; j++)
    {
        L_temp = L_mult (0x3fff, lsf1[j]);
        L_temp = L_mac (L_temp, 0x3fff, lsf2[j]);
        L_temp = L_mult (INV_DTX_HANGOVER_P1, extract_h (L_temp));

        for (i = 0; i < DTX_HANGOVER; i++)
        {
            L_temp = L_mac (L_temp, INV_DTX_HANGOVER_P1, lsf_old[i][j]);
        }

        lsf_aver[j] = extract_h (L_temp);              move16 (); 
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: update_gain_code_history_tx
 *
 *   PURPOSE: Update the fixed codebook gain parameter history of the
 *            encoder. The fixed codebook gain parameters kept in the buffer
 *            are used later for computing the reference fixed codebook
 *            gain parameter value and the averaged fixed codebook gain
 *            parameter value.
 *
 *   INPUTS:      new_gain_code   New fixed codebook gain value
 *
 *                gain_code_old_tx[0..4*DTX_HANGOVER-1]
 *                                Old fixed codebook gain history of encoder
 *
 *   OUTPUTS:     gain_code_old_tx[0..4*DTX_HANGOVER-1]
 *                                Updated fixed codebook gain history of encoder
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void update_gain_code_history_tx (
    struct EFR_encoder_state *st,
    Word16 new_gain_code
)
{
    /* Circular buffer */
    st->gain_code_old_tx[st->buf_p_tx] = new_gain_code;

    if (sub (st->buf_p_tx, (4 * DTX_HANGOVER - 1)) == 0)
    {
        st->buf_p_tx = 0;
    }
    else
    {
        st->buf_p_tx = add (st->buf_p_tx, 1);
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: update_gain_code_history_rx
 *
 *   PURPOSE: Update the fixed codebook gain parameter history of the
 *            decoder. The fixed codebook gain parameters kept in the buffer
 *            are used later for computing the reference fixed codebook
 *            gain parameter value.
 *
 *   INPUTS:      new_gain_code   New fixed codebook gain value
 *
 *                gain_code_old_tx[0..4*DTX_HANGOVER-1]
 *                                Old fixed codebook gain history of decoder
 *
 *   OUTPUTS:     gain_code_old_tx[0..4*DTX_HANGOVER-1]
 *                                Updated fixed codebk gain history of decoder
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void update_gain_code_history_rx (
    struct EFR_decoder_state *st,
    Word16 new_gain_code
)
{
    /* Circular buffer */
    st->gain_code_old_rx[st->buf_p_rx] = new_gain_code;

    if (sub (st->buf_p_rx, (4 * DTX_HANGOVER - 1)) == 0)
    {
        st->buf_p_rx = 0;
    }
    else
    {
        st->buf_p_rx = add (st->buf_p_rx, 1);
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: compute_CN_excitation_gain
 *
 *   PURPOSE: Compute the unquantized fixed codebook gain. Computation is
 *            based on the energy of the Linear Prediction residual signal.
 *
 *   INPUTS:      res2[0..39]   Linear Prediction residual signal
 *
 *   OUTPUTS:     none
 *
 *   RETURN VALUE: Unquantized fixed codebook gain
 *
 *************************************************************************/

Word16 compute_CN_excitation_gain (
    Word16 res2[L_SUBFR]
)
{
    Word16 i, norm, norm1, temp, overfl;
    Word32 L_temp;

    /* Compute the energy of the LP residual signal */

    norm = 0;                                          move16 (); 
    do
    {
        overfl = 0;                                    move16 ();

        L_temp = 0L;                                   move32 (); 
        for (i = 0; i < L_SUBFR; i++)
        {
            temp = shr (res2[i], norm);
            L_temp = L_mac (L_temp, temp, temp);
        }

        test (); 
        if (L_sub (L_temp, MAX_32) == 0)
        {
            norm = add (norm, 1);
            overfl = 1;                 move16 (); /* Set the overflow flag */
        }
        test (); 
    }
    while (overfl != 0);

    L_temp = L_add (L_temp, 1L);             /* Avoid the case of all zeros */

    /* Take the square root of the obtained energy value (sqroot is a 2nd
       order Taylor series approximation) */

    norm1 = norm_l (L_temp);
    temp = extract_h (L_shl (L_temp, norm1));
    L_temp = L_mult (temp, temp);
    L_temp = L_sub (805306368L, L_shr (L_temp, 3));
    L_temp = L_add (L_temp, L_mult (24576, temp));

    temp = extract_h (L_temp);
    test (); logic16 (); 
    if ((norm1 & 0x0001) != 0)
    {
        temp = mult_r (temp, 23170);
        norm1 = sub (norm1, 1);
    }
    /* Divide the result of sqroot operation by sqroot(10) */

    temp = mult_r (temp, 10362);

    /* Re-scale to get the final value */

    norm1 = shr (norm1, 1);
    norm1 = sub (norm1, norm);

    test (); 
    if (norm1 >= 0)
    {
        temp = shr (temp, norm1);
    }
    else
    {
        temp = shl (temp, abs_s (norm1));
    }

    return temp;
}

/*************************************************************************
 *
 *   FUNCTION NAME: update_gcode0_CN
 *
 *   PURPOSE: Update the reference fixed codebook gain parameter value.
 *            The reference value is computed by averaging the quantized
 *            fixed codebook gain parameter values which exist in the
 *            fixed codebook gain parameter history.
 *
 *   INPUTS:      gain_code_old[0..4*DTX_HANGOVER-1]
 *                              fixed codebook gain parameter history
 *
 *   OUTPUTS:     none
 *
 *   RETURN VALUE: Computed reference fixed codebook gain
 *
 *************************************************************************/

Word16 update_gcode0_CN (
    Word16 gain_code_old[4 * DTX_HANGOVER]
)
{
    Word16 i, j;
    Word32 L_temp, L_ret;

    L_ret = 0L;                                        move32 (); 
    for (i = 0; i < DTX_HANGOVER; i++)
    {
        L_temp = L_mult (0x1fff, gain_code_old[4 * i]);
        for (j = 1; j < 4; j++)
        {
            L_temp = L_mac (L_temp, 0x1fff, gain_code_old[4 * i + j]);
        }
        L_ret = L_mac (L_ret, INV_DTX_HANGOVER, extract_h (L_temp));
    }

    return extract_h (L_ret);
}

/*************************************************************************
 *
 *   FUNCTION NAME: aver_gain_code_history
 *
 *   PURPOSE: Compute the averaged fixed codebook gain parameter value.
 *            Computation is performed by averaging the fixed codebook
 *            gain parameter values which exist in the fixed codebook
 *            gain parameter history, together with the fixed codebook
 *            gain parameter value of the current subframe.
 *
 *   INPUTS:      CN_excitation_gain
 *                              Unquantized fixed codebook gain value
 *                              of the current subframe
 *                gain_code_old[0..4*DTX_HANGOVER-1]
 *                              fixed codebook gain parameter history
 *
 *   OUTPUTS:     none
 *
 *   RETURN VALUE: Averaged fixed codebook gain value
 *
 *************************************************************************/

Word16 aver_gain_code_history (
    Word16 CN_excitation_gain,
    Word16 gain_code_old[4 * DTX_HANGOVER]
)
{
    Word16 i;
    Word32 L_ret;

    L_ret = L_mult (0x470, CN_excitation_gain);

    for (i = 0; i < (4 * DTX_HANGOVER); i++)
    {
        L_ret = L_mac (L_ret, 0x470, gain_code_old[i]);
    }
    return extract_h (L_ret);
}

/*************************************************************************
 *
 *   FUNCTION NAME: build_CN_code
 *
 *   PURPOSE: Compute the comfort noise fixed codebook excitation. The
 *            gains of the pulses are always +/-1.
 *
 *   INPUTS:      *seed         Old CN generator shift register state
 *
 *   OUTPUTS:     cod[0..39]    Generated comfort noise fixed codebook vector
 *                *seed         Updated CN generator shift register state
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void build_CN_code (
    Word16 cod[],
    Word32 *seed
)
{
    Word16 i, j, k;

    for (i = 0; i < L_SUBFR; i++)
    {
        cod[i] = 0;                                    move16 (); 
    }

    for (k = 0; k < NB_PULSE; k++)
    {
        i = pseudonoise (seed, 2);      /* generate pulse position */
        i = shr (extract_l (L_mult (i, 10)), 1);
        i = add (i, k);

        j = pseudonoise (seed, 1);      /* generate sign           */

        test (); 
        if (j > 0)
        {
            cod[i] = 4096;                             move16 (); 
        }
        else
        {
            cod[i] = -4096;                            move16 (); 
        }
    }

    return;
}

/*************************************************************************
 *
 *   FUNCTION NAME: pseudonoise
 *
 *   PURPOSE: Generate a random integer value to use in comfort noise
 *            generation. The algorithm uses polynomial x^31 + x^3 + 1
 *            (length of PN sequence is 2^31 - 1).
 *
 *   INPUTS:      *shift_reg    Old CN generator shift register state
 *
 *
 *   OUTPUTS:     *shift_reg    Updated CN generator shift register state
 *
 *   RETURN VALUE: Generated random integer value
 *
 *************************************************************************/

Word16 pseudonoise (
    Word32 *shift_reg,
    Word16 no_bits
)
{
    Word16 noise_bits, Sn, i;

    noise_bits = 0;                                    move16 (); 
    for (i = 0; i < no_bits; i++)
    {
        /* State n == 31 */
        test (); logic32 (); 
        if ((*shift_reg & 0x00000001L) != 0)
        {
            Sn = 1;                                    move16 (); 
        }
        else
        {
            Sn = 0;                                    move16 (); 
        }

        /* State n == 3 */
        test (); logic32 (); 
        if ((*shift_reg & 0x10000000L) != 0)
        {
            Sn = Sn ^ 1;                               logic16 (); 
        }
        else
        {
            Sn = Sn ^ 0;                               logic16 (); 
        }

        noise_bits = shl (noise_bits, 1);
        noise_bits = noise_bits | (extract_l (*shift_reg) & 1);
        logic16 (); logic16 (); 

        *shift_reg = L_shr (*shift_reg, 1);            move32 (); 
        test (); logic16 (); 
        if (Sn & 1)
        {
            *shift_reg = *shift_reg | 0x40000000L;     move32 (); logic32 (); 
        }
    }

    return noise_bits;
}

/*************************************************************************
 *
 *   FUNCTION NAME: interpolate_CN_param
 *
 *   PURPOSE: Interpolate a comfort noise parameter value over the comfort
 *            noise update period.
 *
 *   INPUTS:      old_param     The older parameter of the interpolation
 *                              (the endpoint the interpolation is started
 *                              from)
 *                new_param     The newer parameter of the interpolation
 *                              (the endpoint the interpolation is ended to)
 *                rx_dtx_state  State of the comfort noise insertion period
 *
 *   OUTPUTS:     none
 *
 *   RETURN VALUE: Interpolated CN parameter value
 *
 *************************************************************************/

Word16 interpolate_CN_param (
    Word16 old_param,
    Word16 new_param,
    Word16 rx_dtx_state
)
{
    static const Word16 interp_factor[CN_INT_PERIOD] =
    {
        0x0555, 0x0aaa, 0x1000, 0x1555, 0x1aaa, 0x2000,
        0x2555, 0x2aaa, 0x3000, 0x3555, 0x3aaa, 0x4000,
        0x4555, 0x4aaa, 0x5000, 0x5555, 0x5aaa, 0x6000,
        0x6555, 0x6aaa, 0x7000, 0x7555, 0x7aaa, 0x7fff};
    Word16 temp;
    Word32 L_temp;

    L_temp = L_mult (interp_factor[rx_dtx_state], new_param);
    temp = sub (0x7fff, interp_factor[rx_dtx_state]);
    temp = add (temp, 1);
    L_temp = L_mac (L_temp, temp, old_param);
    temp = round (L_temp);

    return temp;
}

/*************************************************************************
 *
 *   FUNCTION NAME:  interpolate_CN_lsf
 *
 *   PURPOSE: Interpolate comfort noise LSF parameter vector over the comfort
 *            noise update period.
 *
 *   INPUTS:      lsf_old_CN[0..9]
 *                              The older LSF parameter vector of the
 *                              interpolation (the endpoint the interpolation
 *                              is started from)
 *                lsf_new_CN[0..9]
 *                              The newer LSF parameter vector of the
 *                              interpolation (the endpoint the interpolation
 *                              is ended to)
 *                rx_dtx_state  State of the comfort noise insertion period
 *
 *   OUTPUTS:     lsf_interp_CN[0..9]
 *                              Interpolated LSF parameter vector
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/

void interpolate_CN_lsf (
    Word16 lsf_old_CN[M],
    Word16 lsf_new_CN[M],
    Word16 lsf_interp_CN[M],
    Word16 rx_dtx_state
)
{
    Word16 i;

    for (i = 0; i < M; i++)
    {
        lsf_interp_CN[i] = interpolate_CN_param (lsf_old_CN[i],
                                                 lsf_new_CN[i],
                                                 rx_dtx_state); move16 (); 
    }

    return;
}