static void Gsm_RPE_Decoding(gsmword xmaxcr, gsmword Mcr, gsmword *xMcr, gsmword *erp)
{
gsmword exp, mant;
gsmword xMp[ 13 ];
APCM_quantization_xmaxc_to_exp_mant(xmaxcr, &exp, &mant);
APCM_inverse_quantization(xMcr, mant, exp, xMp);
RPE_grid_positioning(Mcr, xMp, erp);
}
void Gsm_RPE_Decoding(struct gsm_state *S, int16_t xmaxcr, int16_t Mcr, int16_t * xMcr, /* [0..12], 3 bits IN */
int16_t * erp /* [0..39] OUT */
)
{
(void)S;
int16_t exp, mant;
int16_t xMp[13];
APCM_quantization_xmaxc_to_exp_mant(xmaxcr, &exp, &mant);
APCM_inverse_quantization(xMcr, mant, exp, xMp);
RPE_grid_positioning(Mcr, xMp, erp);
}
void Gsm_RPE_Decoding (
/*-struct gsm_state * S,-*/
word xmaxcr,
word Mcr,
word * xMcr, /* [0..12], 3 bits IN */
word * erp /* [0..39] OUT */
)
{
word expon, mant;
word xMp[ 13 ];
APCM_quantization_xmaxc_to_exp_mant( xmaxcr, &expon, &mant );
APCM_inverse_quantization( xMcr, mant, expon, xMp );
RPE_grid_positioning( Mcr, xMp, erp );
}
static void APCM_quantization (
word * xM, /* [0..12] IN */
word * xMc, /* [0..12] OUT */
word * mant_out, /* OUT */
word * exp_out, /* OUT */
word * xmaxc_out /* OUT */
)
{
int i, itest;
word xmax, xmaxc, temp, temp1, temp2;
word exp, mant;
/* Find the maximum absolute value xmax of xM[0..12].
*/
xmax = 0;
for (i = 0; i <= 12; i++) {
temp = xM[i];
temp = GSM_ABS(temp);
if (temp > xmax) xmax = temp;
}
/* Qantizing and coding of xmax to get xmaxc.
*/
exp = 0;
temp = SASR( xmax, 9 );
itest = 0;
for (i = 0; i <= 5; i++) {
itest |= (temp <= 0);
temp = SASR( temp, 1 );
assert(exp <= 5);
if (itest == 0) exp++; /* exp = add (exp, 1) */
}
assert(exp <= 6 && exp >= 0);
temp = exp + 5;
assert(temp <= 11 && temp >= 0);
xmaxc = gsm_add( SASR(xmax, temp), exp << 3 );
/* Quantizing and coding of the xM[0..12] RPE sequence
* to get the xMc[0..12]
*/
APCM_quantization_xmaxc_to_exp_mant( xmaxc, &exp, &mant );
/* This computation uses the fact that the decoded version of xmaxc
* can be calculated by using the exponent and the mantissa part of
* xmaxc (logarithmic table).
* So, this method avoids any division and uses only a scaling
* of the RPE samples by a function of the exponent. A direct
* multiplication by the inverse of the mantissa (NRFAC[0..7]
* found in table 4.5) gives the 3 bit coded version xMc[0..12]
* of the RPE samples.
*/
/* Direct computation of xMc[0..12] using table 4.5
*/
assert( exp <= 4096 && exp >= -4096);
assert( mant >= 0 && mant <= 7 );
temp1 = 6 - exp; /* normalization by the exponent */
temp2 = gsm_NRFAC[ mant ]; /* inverse mantissa */
for (i = 0; i <= 12; i++) {
assert(temp1 >= 0 && temp1 < 16);
temp = xM[i] << temp1;
temp = GSM_MULT( temp, temp2 );
temp = SASR(temp, 12);
xMc[i] = temp + 4; /* see note below */
}
/* NOTE: This equation is used to make all the xMc[i] positive.
*/
*mant_out = mant;
*exp_out = exp;
*xmaxc_out = xmaxc;
}
