ref: 273089322f62e5b01d40228bf8095d9414f5d778
dir: /src/g723_24.c/
/*
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* Sun Microsystems, Inc.
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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 "st.h"
#include "libst.h"
#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(sl, in_coding, state_ptr)
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 = st_Alaw_to_linear(sl) >> 2;
break;
case AUDIO_ENCODING_ULAW:
sl = st_ulaw_to_linear(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(i, out_coding, state_ptr)
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);
}
}