ref: b7cb7cf9368d4139a02b8c37f1d87835e526c5e2
dir: /src/libgsm/long_term.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"
/*
* 4.2.11 .. 4.2.12 LONG TERM PREDICTOR (LTP) SECTION
*/
/*
* This module computes the LTP gain (bc) and the LTP lag (Nc)
* for the long term analysis filter. This is done by calculating a
* maximum of the cross-correlation function between the current
* sub-segment short term residual signal d[0..39] (output of
* the short term analysis filter; for simplification the index
* of this array begins at 0 and ends at 39 for each sub-segment of the
* RPE-LTP analysis) and the previous reconstructed short term
* residual signal dp[ -120 .. -1 ]. A dynamic scaling must be
* performed to avoid overflow.
*/
static void Calculation_of_the_LTP_parameters (
register word * d, /* [0..39] IN */
register word * dp, /* [-120..-1] IN */
word * bc_out, /* OUT */
word * Nc_out /* OUT */
)
{
register int k, lambda;
word Nc, bc;
word wt[40];
longword L_max, L_power;
word R, S, dmax, scal;
register word temp;
/* Search of the optimum scaling of d[0..39].
*/
dmax = 0;
for (k = 0; k <= 39; k++) {
temp = d[k];
temp = GSM_ABS( temp );
if (temp > dmax) dmax = temp;
}
temp = 0;
if (dmax == 0) scal = 0;
else {
assert(dmax > 0);
temp = gsm_norm( (longword)dmax << 16 );
}
if (temp > 6) scal = 0;
else scal = 6 - temp;
assert(scal >= 0);
/* Initialization of a working array wt
*/
for (k = 0; k <= 39; k++) wt[k] = SASR( d[k], scal );
/* Search for the maximum cross-correlation and coding of the LTP lag
*/
L_max = 0;
Nc = 40; /* index for the maximum cross-correlation */
for (lambda = 40; lambda <= 120; lambda++) {
# undef STEP
# define STEP(k) (longword)wt[k] * dp[k - lambda]
register longword L_result;
L_result = STEP(0) ; L_result += STEP(1) ;
L_result += STEP(2) ; L_result += STEP(3) ;
L_result += STEP(4) ; L_result += STEP(5) ;
L_result += STEP(6) ; L_result += STEP(7) ;
L_result += STEP(8) ; L_result += STEP(9) ;
L_result += STEP(10) ; L_result += STEP(11) ;
L_result += STEP(12) ; L_result += STEP(13) ;
L_result += STEP(14) ; L_result += STEP(15) ;
L_result += STEP(16) ; L_result += STEP(17) ;
L_result += STEP(18) ; L_result += STEP(19) ;
L_result += STEP(20) ; L_result += STEP(21) ;
L_result += STEP(22) ; L_result += STEP(23) ;
L_result += STEP(24) ; L_result += STEP(25) ;
L_result += STEP(26) ; L_result += STEP(27) ;
L_result += STEP(28) ; L_result += STEP(29) ;
L_result += STEP(30) ; L_result += STEP(31) ;
L_result += STEP(32) ; L_result += STEP(33) ;
L_result += STEP(34) ; L_result += STEP(35) ;
L_result += STEP(36) ; L_result += STEP(37) ;
L_result += STEP(38) ; L_result += STEP(39) ;
if (L_result > L_max) {
Nc = lambda;
L_max = L_result;
}
}
*Nc_out = Nc;
L_max <<= 1;
/* Rescaling of L_max
*/
assert(scal <= 100 && scal >= -100);
L_max = L_max >> (6 - scal); /* sub(6, scal) */
assert( Nc <= 120 && Nc >= 40);
/* Compute the power of the reconstructed short term residual
* signal dp[..]
*/
L_power = 0;
for (k = 0; k <= 39; k++) {
register longword L_temp;
L_temp = SASR( dp[k - Nc], 3 );
L_power += L_temp * L_temp;
}
L_power <<= 1; /* from L_MULT */
/* Normalization of L_max and L_power
*/
if (L_max <= 0) {
*bc_out = 0;
return;
}
if (L_max >= L_power) {
*bc_out = 3;
return;
}
temp = gsm_norm( L_power );
R = SASR( L_max << temp, 16 );
S = SASR( L_power << temp, 16 );
/* Coding of the LTP gain
*/
/* Table 4.3a must be used to obtain the level DLB[i] for the
* quantization of the LTP gain b to get the coded version bc.
*/
for (bc = 0; bc <= 2; bc++) if (R <= gsm_mult(S, gsm_DLB[bc])) break;
*bc_out = bc;
}
/* 4.2.12 */
static void Long_term_analysis_filtering (
word bc, /* IN */
word Nc, /* IN */
register word * dp, /* previous d [-120..-1] IN */
register word * d, /* d [0..39] IN */
register word * dpp, /* estimate [0..39] OUT */
register word * e /* long term res. signal [0..39] OUT */
)
/*
* In this part, we have to decode the bc parameter to compute
* the samples of the estimate dpp[0..39]. The decoding of bc needs the
* use of table 4.3b. The long term residual signal e[0..39]
* is then calculated to be fed to the RPE encoding section.
*/
{
register int k;
register longword ltmp;
# undef STEP
# define STEP(BP) \
for (k = 0; k <= 39; k++) { \
dpp[k] = GSM_MULT_R( BP, dp[k - Nc]); \
e[k] = GSM_SUB( d[k], dpp[k] ); \
}
switch (bc) {
case 0: STEP( 3277 ); break;
case 1: STEP( 11469 ); break;
case 2: STEP( 21299 ); break;
case 3: STEP( 32767 ); break;
}
}
void Gsm_Long_Term_Predictor ( /* 4x for 160 samples */
word * d, /* [0..39] residual signal IN */
word * dp, /* [-120..-1] d' IN */
word * e, /* [0..39] OUT */
word * dpp, /* [0..39] OUT */
word * Nc, /* correlation lag OUT */
word * bc /* gain factor OUT */
)
{
assert( d ); assert( dp ); assert( e );
assert( dpp); assert( Nc ); assert( bc );
Calculation_of_the_LTP_parameters(d, dp, bc, Nc);
Long_term_analysis_filtering( *bc, *Nc, dp, d, dpp, e );
}
/* 4.3.2 */
void Gsm_Long_Term_Synthesis_Filtering (
struct gsm_state * S,
word Ncr,
word bcr,
register word * erp, /* [0..39] IN */
register word * drp /* [-120..-1] IN, [-120..40] OUT */
)
/*
* This procedure uses the bcr and Ncr parameter to realize the
* long term synthesis filtering. The decoding of bcr needs
* table 4.3b.
*/
{
register longword ltmp; /* for ADD */
register int k;
word brp, drpp, Nr;
/* Check the limits of Nr.
*/
Nr = Ncr < 40 || Ncr > 120 ? S->nrp : Ncr;
S->nrp = Nr;
assert(Nr >= 40 && Nr <= 120);
/* Decoding of the LTP gain bcr
*/
brp = gsm_QLB[ bcr ];
/* Computation of the reconstructed short term residual
* signal drp[0..39]
*/
assert(brp != MIN_WORD);
for (k = 0; k <= 39; k++) {
drpp = GSM_MULT_R( brp, drp[ k - Nr ] );
drp[k] = GSM_ADD( erp[k], drpp );
}
/*
* Update of the reconstructed short term residual signal
* drp[ -1..-120 ]
*/
for (k = 0; k <= 119; k++) drp[ -120 + k ] = drp[ -80 + k ];
}