g723_24.c

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 * Sun Microsystems, Inc.
 * 2550 Garcia Avenue
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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 "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 >>= 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);
    }
}