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/*
* g723_40.c
*
* Description:
*
* g723_40_encoder(), g723_40_decoder()
*
* These routines comprise an implementation of the CCITT G.723 40Kbps
* 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.
*
* The deviation from the bit level specification (lookup tables),
* preserves the bit level performance specifications.
*
* As outlined in the G.723 Recommendation, the algorithm is broken
* down into modules. Each section of code below is preceded by
* the name of the module which it is implementing.
*
*/
#include "g72x.h"
/*
* Maps G.723_40 code word to ructeconstructed scale factor normalized log
* magnitude values.
*/
static short _dqlntab[32] = { -2048, -66, 28, 104, 169, 224, 274, 318,
358, 395, 429, 459, 488, 514, 539, 566,
566, 539, 514, 488, 459, 429, 395, 358,
318, 274, 224, 169, 104, 28, -66, -2048};
/* Maps G.723_40 code word to log of scale factor multiplier. */
static short _witab[32] = {448, 448, 768, 1248, 1280, 1312, 1856, 3200,
4512, 5728, 7008, 8960, 11456, 14080, 16928, 22272,
22272, 16928, 14080, 11456, 8960, 7008, 5728, 4512,
3200, 1856, 1312, 1280, 1248, 768, 448, 448};
/*
* Maps G.723_40 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[32] = {0, 0, 0, 0, 0, 0x200, 0x200, 0x200,
0x200, 0x200, 0x400, 0x600, 0x800, 0xA00, 0xC00, 0xC00,
0xC00, 0xC00, 0xA00, 0x800, 0x600, 0x400, 0x200, 0x200,
0x200, 0x200, 0x200, 0, 0, 0, 0, 0};
static short qtab_723_40[15] = { -122, -16, 68, 139, 198, 250, 298, 339,
378, 413, 445, 475, 502, 528, 553};
/*
* g723_40_encoder()
*
* Encodes a 16-bit linear PCM, A-law or u-law input sample and retuens
* the resulting 5-bit CCITT G.723 40Kbps code.
* Returns -1 if the input coding value is invalid.
*/
int
g723_40_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 difference */
/* quantize prediction difference */
y = step_size(state_ptr); /* adaptive quantizer step size */
i = quantize(d, y, qtab_723_40, 15); /* i = ADPCM code */
dq = reconstruct(i & 0x10, _dqlntab[i], y); /* quantized diff */
sr = (dq < 0) ? se - (dq & 0x7FFF) : se + dq; /* reconstructed signal */
dqsez = sr + sez - se; /* dqsez = pole prediction diff. */
update(5, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
return (i);
}
/*
* g723_40_decoder()
*
* Decodes a 5-bit CCITT G.723 40Kbps 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_40_decoder(
int i,
int out_coding,
struct g72x_state *state_ptr)
{
short sezi, sei, sez, se; /* ACCUM */
short y /*, dif */; /* MIX */
short sr; /* ADDB */
short dq;
short dqsez;
i &= 0x1f; /* 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 & 0x10, _dqlntab[i], y); /* estimation diff. */
sr = (dq < 0) ? (se - (dq & 0x7FFF)) : (se + dq); /* reconst. signal */
dqsez = sr - se + sez; /* pole prediction diff. */
update(5, 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, 0x10, qtab_723_40));
case AUDIO_ENCODING_ULAW:
return (tandem_adjust_ulaw(sr, se, y, i, 0x10, qtab_723_40));
case AUDIO_ENCODING_LINEAR:
return (sr << 2); /* sr was of 14-bit dynamic range */
default:
return ( -1);
}
}
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