ref: 2515cb2de68b10eff93b876159dcbf180474f146
dir: /src/libgsm/rpe.c/
/*
* Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
* Universitaet Berlin. See the accompanying file "COPYRIGHT" for
* details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
*/
#include <stdio.h>
#include <assert.h>
#include "private.h"
#include "gsm.h"
/* 4.2.13 .. 4.2.17 RPE ENCODING SECTION
*/
/* 4.2.13 */
static void Weighting_filter (
register word * e, /* signal [-5..0.39.44] IN */
word * x /* signal [0..39] OUT */
)
/*
* The coefficients of the weighting filter are stored in a table
* (see table 4.4). The following scaling is used:
*
* H[0..10] = integer( real_H[ 0..10] * 8192 );
*/
{
/* word wt[ 50 ]; */
register longword L_result;
register int k /* , i */ ;
/* Initialization of a temporary working array wt[0...49]
*/
/* for (k = 0; k <= 4; k++) wt[k] = 0;
* for (k = 5; k <= 44; k++) wt[k] = *e++;
* for (k = 45; k <= 49; k++) wt[k] = 0;
*
* (e[-5..-1] and e[40..44] are allocated by the caller,
* are initially zero and are not written anywhere.)
*/
e -= 5;
/* Compute the signal x[0..39]
*/
for (k = 0; k <= 39; k++) {
L_result = 8192 >> 1;
/* for (i = 0; i <= 10; i++) {
* L_temp = GSM_L_MULT( wt[k+i], gsm_H[i] );
* L_result = GSM_L_ADD( L_result, L_temp );
* }
*/
#undef STEP
#define STEP( i, H ) (e[ k + i ] * (longword)H)
/* Every one of these multiplications is done twice --
* but I don't see an elegant way to optimize this.
* Do you?
*/
L_result +=
STEP( 0, -134 )
+ STEP( 1, -374 )
/* + STEP( 2, 0 ) */
+ STEP( 3, 2054 )
+ STEP( 4, 5741 )
+ STEP( 5, 8192 )
+ STEP( 6, 5741 )
+ STEP( 7, 2054 )
/* + STEP( 8, 0 ) */
+ STEP( 9, -374 )
+ STEP(10, -134 )
;
/* L_result = GSM_L_ADD( L_result, L_result ); (* scaling(x2) *)
* L_result = GSM_L_ADD( L_result, L_result ); (* scaling(x4) *)
*
* x[k] = SASR( L_result, 16 );
*/
/* 2 adds vs. >>16 => 14, minus one shift to compensate for
* those we lost when replacing L_MULT by '*'.
*/
L_result = SASR( L_result, 13 );
x[k] = ( L_result < MIN_WORD ? MIN_WORD
: (L_result > MAX_WORD ? MAX_WORD : L_result ));
}
}
/* 4.2.14 */
static void RPE_grid_selection (
word * x, /* [0..39] IN */
word * xM, /* [0..12] OUT */
word * Mc_out /* OUT */
)
/*
* The signal x[0..39] is used to select the RPE grid which is
* represented by Mc.
*/
{
/* register word temp1; */
register int /* m, */ i;
register longword L_result, L_temp;
longword EM; /* xxx should be L_EM? */
word Mc;
longword L_common_0_3;
EM = 0;
Mc = 0;
/* for (m = 0; m <= 3; m++) {
* L_result = 0;
*
*
* for (i = 0; i <= 12; i++) {
*
* temp1 = SASR( x[m + 3*i], 2 );
*
* assert(temp1 != MIN_WORD);
*
* L_temp = GSM_L_MULT( temp1, temp1 );
* L_result = GSM_L_ADD( L_temp, L_result );
* }
*
* if (L_result > EM) {
* Mc = m;
* EM = L_result;
* }
* }
*/
#undef STEP
#define STEP( m, i ) L_temp = SASR( x[m + 3 * i], 2 ); \
L_result += L_temp * L_temp;
/* common part of 0 and 3 */
L_result = 0;
STEP( 0, 1 ); STEP( 0, 2 ); STEP( 0, 3 ); STEP( 0, 4 );
STEP( 0, 5 ); STEP( 0, 6 ); STEP( 0, 7 ); STEP( 0, 8 );
STEP( 0, 9 ); STEP( 0, 10); STEP( 0, 11); STEP( 0, 12);
L_common_0_3 = L_result;
/* i = 0 */
STEP( 0, 0 );
L_result <<= 1; /* implicit in L_MULT */
EM = L_result;
/* i = 1 */
L_result = 0;
STEP( 1, 0 );
STEP( 1, 1 ); STEP( 1, 2 ); STEP( 1, 3 ); STEP( 1, 4 );
STEP( 1, 5 ); STEP( 1, 6 ); STEP( 1, 7 ); STEP( 1, 8 );
STEP( 1, 9 ); STEP( 1, 10); STEP( 1, 11); STEP( 1, 12);
L_result <<= 1;
if (L_result > EM) {
Mc = 1;
EM = L_result;
}
/* i = 2 */
L_result = 0;
STEP( 2, 0 );
STEP( 2, 1 ); STEP( 2, 2 ); STEP( 2, 3 ); STEP( 2, 4 );
STEP( 2, 5 ); STEP( 2, 6 ); STEP( 2, 7 ); STEP( 2, 8 );
STEP( 2, 9 ); STEP( 2, 10); STEP( 2, 11); STEP( 2, 12);
L_result <<= 1;
if (L_result > EM) {
Mc = 2;
EM = L_result;
}
/* i = 3 */
L_result = L_common_0_3;
STEP( 3, 12 );
L_result <<= 1;
if (L_result > EM) {
Mc = 3;
EM = L_result;
}
/**/
/* Down-sampling by a factor 3 to get the selected xM[0..12]
* RPE sequence.
*/
for (i = 0; i <= 12; i ++) xM[i] = x[Mc + 3*i];
*Mc_out = Mc;
}
/* 4.12.15 */
static void APCM_quantization_xmaxc_to_exp_mant (
word xmaxc, /* IN */
word * exp_out, /* OUT */
word * mant_out ) /* OUT */
{
word exp, mant;
/* Compute exponent and mantissa of the decoded version of xmaxc
*/
exp = 0;
if (xmaxc > 15) exp = SASR(xmaxc, 3) - 1;
mant = xmaxc - (exp << 3);
if (mant == 0) {
exp = -4;
mant = 7;
}
else {
while (mant <= 7) {
mant = mant << 1 | 1;
exp--;
}
mant -= 8;
}
assert( exp >= -4 && exp <= 6 );
assert( mant >= 0 && mant <= 7 );
*exp_out = exp;
*mant_out = mant;
}
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;
}
/* 4.2.16 */
static void APCM_inverse_quantization (
register word * xMc, /* [0..12] IN */
word mant,
word exp,
register word * xMp) /* [0..12] OUT */
/*
* This part is for decoding the RPE sequence of coded xMc[0..12]
* samples to obtain the xMp[0..12] array. Table 4.6 is used to get
* the mantissa of xmaxc (FAC[0..7]).
*/
{
int i;
word temp, temp1, temp2, temp3;
longword ltmp;
assert( mant >= 0 && mant <= 7 );
temp1 = gsm_FAC[ mant ]; /* see 4.2-15 for mant */
temp2 = gsm_sub( 6, exp ); /* see 4.2-15 for exp */
temp3 = gsm_asl( 1, gsm_sub( temp2, 1 ));
for (i = 13; i--;) {
assert( *xMc <= 7 && *xMc >= 0 ); /* 3 bit unsigned */
/* temp = gsm_sub( *xMc++ << 1, 7 ); */
temp = (*xMc++ << 1) - 7; /* restore sign */
assert( temp <= 7 && temp >= -7 ); /* 4 bit signed */
temp <<= 12; /* 16 bit signed */
temp = GSM_MULT_R( temp1, temp );
temp = GSM_ADD( temp, temp3 );
*xMp++ = gsm_asr( temp, temp2 );
}
}
/* 4.2.17 */
static void RPE_grid_positioning (
word Mc, /* grid position IN */
register word * xMp, /* [0..12] IN */
register word * ep /* [0..39] OUT */
)
/*
* This procedure computes the reconstructed long term residual signal
* ep[0..39] for the LTP analysis filter. The inputs are the Mc
* which is the grid position selection and the xMp[0..12] decoded
* RPE samples which are upsampled by a factor of 3 by inserting zero
* values.
*/
{
int i = 13;
assert(0 <= Mc && Mc <= 3);
switch (Mc) {
case 3: *ep++ = 0;
case 2: do {
*ep++ = 0;
case 1: *ep++ = 0;
case 0: *ep++ = *xMp++;
} while (--i);
}
while (++Mc < 4) *ep++ = 0;
/*
int i, k;
for (k = 0; k <= 39; k++) ep[k] = 0;
for (i = 0; i <= 12; i++) {
ep[ Mc + (3*i) ] = xMp[i];
}
*/
}
/* 4.2.18 */
/* This procedure adds the reconstructed long term residual signal
* ep[0..39] to the estimated signal dpp[0..39] from the long term
* analysis filter to compute the reconstructed short term residual
* signal dp[-40..-1]; also the reconstructed short term residual
* array dp[-120..-41] is updated.
*/
#if 0 /* Has been inlined in code.c */
void Gsm_Update_of_reconstructed_short_time_residual_signal P3((dpp, ep, dp),
word * dpp, /* [0...39] IN */
word * ep, /* [0...39] IN */
word * dp) /* [-120...-1] IN/OUT */
{
int k;
for (k = 0; k <= 79; k++)
dp[ -120 + k ] = dp[ -80 + k ];
for (k = 0; k <= 39; k++)
dp[ -40 + k ] = gsm_add( ep[k], dpp[k] );
}
#endif /* Has been inlined in code.c */
void Gsm_RPE_Encoding (
word * e, /* -5..-1][0..39][40..44 IN/OUT */
word * xmaxc, /* OUT */
word * Mc, /* OUT */
word * xMc) /* [0..12] OUT */
{
word x[40];
word xM[13], xMp[13];
word mant, exp;
Weighting_filter(e, x);
RPE_grid_selection(x, xM, Mc);
APCM_quantization( xM, xMc, &mant, &exp, xmaxc);
APCM_inverse_quantization( xMc, mant, exp, xMp);
RPE_grid_positioning( *Mc, xMp, e );
}
void Gsm_RPE_Decoding (
word xmaxcr,
word Mcr,
word * xMcr, /* [0..12], 3 bits IN */
word * erp /* [0..39] OUT */
)
{
word exp, mant;
word xMp[ 13 ];
APCM_quantization_xmaxc_to_exp_mant( xmaxcr, &exp, &mant );
APCM_inverse_quantization( xMcr, mant, exp, xMp );
RPE_grid_positioning( Mcr, xMp, erp );
}