g723_24.cpp

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/*
 * g723_24.c
 *
 * Description:
 *
 * g723_24_encoder(), g723_24_decoder()
 *
 * These routines comprise an implementation of the CCITT G.723 24 Kbps
 * ADPCM coding algorithm.  Essentially, this implementation is identical to
 * the bit level description except for a few deviations which take advantage
 * of workstation attributes, such as hardware 2's complement arithmetic.
 *
 */
#include "wx/wxprec.h"
#include "wx/mmedia/internal/g72x.h"

/*
 * Maps G.723_24 code word to reconstructed scale factor normalized log
 * magnitude values.
 */
static short _dqlntab[8] = {-2048, 135, 273, 373, 373, 273, 135, -2048};

/* Maps G.723_24 code word to log of scale factor multiplier. */
static short _witab[8] = {-128, 960, 4384, 18624, 18624, 4384, 960, -128};

/*
 * Maps G.723_24 code words to a set of values whose long and short
 * term averages are computed and then compared to give an indication
 * how stationary (steady state) the signal is.
 */
static short _fitab[8] = {0, 0x200, 0x400, 0xE00, 0xE00, 0x400, 0x200, 0};

static short qtab_723_24[3] = {8, 218, 331};

/*
 * g723_24_encoder()
 *
 * Encodes a linear PCM, A-law or u-law input sample and returns its 3-bit code.
 * Returns -1 if invalid input coding value.
 */
int
g723_24_encoder(
    int                sl,
    int                in_coding,
    struct g72x_state *state_ptr)
{
    short        sei, sezi, se, sez;    /* ACCUM */
    short        d;                     /* SUBTA */
    short        y;                     /* MIX */
    short        sr;                    /* ADDB */
    short        dqsez;                 /* ADDC */
    short        dq, i;

    switch (in_coding) {    /* linearize input sample to 14-bit PCM */
    case AUDIO_ENCODING_ALAW:
        sl = alaw2linear(sl) >> 2;
        break;
    case AUDIO_ENCODING_ULAW:
        sl = ulaw2linear(sl) >> 2;
        break;
    case AUDIO_ENCODING_LINEAR:
        sl = ((short)sl) >> 2;        /* sl of 14-bit dynamic range */
        break;
    default:
        return (-1);
    }

    sezi = predictor_zero(state_ptr);
    sez = sezi >> 1;
    sei = sezi + predictor_pole(state_ptr);
    se = sei >> 1;            /* se = estimated signal */

    d = sl - se;            /* d = estimation diff. */

    /* quantize prediction difference d */
    y = step_size(state_ptr);    /* quantizer step size */
    i = quantize(d, y, qtab_723_24, 3);    /* i = ADPCM code */
    dq = reconstruct(i & 4, _dqlntab[i], y); /* quantized diff. */

    sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq; /* reconstructed signal */

    dqsez = sr + sez - se;        /* pole prediction diff. */

    update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);

    return (i);
}

/*
 * g723_24_decoder()
 *
 * Decodes a 3-bit CCITT G.723_24 ADPCM code and returns
 * the resulting 16-bit linear PCM, A-law or u-law sample value.
 * -1 is returned if the output coding is unknown.
 */
int
g723_24_decoder(
    int                i,
    int                out_coding,
    struct g72x_state *state_ptr)
{
    short        sezi, sei, sez, se;    /* ACCUM */
    short        y;                     /* MIX */
    short        sr;                    /* ADDB */
    short        dq;
    short        dqsez;

    i &= 0x07;            /* mask to get proper bits */
    sezi = predictor_zero(state_ptr);
    sez = sezi >> 1;
    sei = sezi + predictor_pole(state_ptr);
    se = sei >> 1;            /* se = estimated signal */

    y = step_size(state_ptr);    /* adaptive quantizer step size */
    dq = reconstruct(i & 0x04, _dqlntab[i], y); /* unquantize pred diff */

    sr = (dq < 0) ? (se - (dq & 0x3FFF)) : (se + dq); /* reconst. signal */

    dqsez = sr - se + sez;            /* pole prediction diff. */

    update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);

    switch (out_coding) {
    case AUDIO_ENCODING_ALAW:
        return (tandem_adjust_alaw(sr, se, y, i, 4, qtab_723_24));
    case AUDIO_ENCODING_ULAW:
        return (tandem_adjust_ulaw(sr, se, y, i, 4, qtab_723_24));
    case AUDIO_ENCODING_LINEAR:
        return (sr << 2);    /* sr was of 14-bit dynamic range */
    default:
        return (-1);
    }
}