rpe.c

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/*
 * 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.
 */

/* $Header$ */

#include <stdio.h>
#include <assert.h>

#include "private.h"

#include "gsm.h"
#include "proto.h"

/* 4.2.13 .. 4.2.17 RPE ENCODING SECTION
 */

/* 4.2.13 */
#ifdef K6OPT
#include "k6opt.h"
#else
static void Weighting_filter P2((e, x),
 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?
 */

#ifdef STUPID_COMPILER
 L_result += STEP( 0, -134 ) ;
 L_result += STEP( 1, -374 ) ;
 /* + STEP( 2, 0 ) */
 L_result += STEP( 3, 2054 ) ;
 L_result += STEP( 4, 5741 ) ;
 L_result += STEP( 5, 8192 ) ;
 L_result += STEP( 6, 5741 ) ;
 L_result += STEP( 7, 2054 ) ;
 /* + STEP( 8, 0 ) */
 L_result += STEP( 9, -374 ) ;
 L_result += STEP( 10, -134 ) ;
#else
 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 )
 ;
#endif

 /* 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] = (word)( L_result < MIN_WORD ? MIN_WORD
 : (L_result > MAX_WORD ? MAX_WORD : L_result ));
 }
}
#endif /* K6OPT */

/* 4.2.14 */

static void RPE_grid_selection P3((x,xM,Mc_out),
 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 P3((xmaxc,exp_out,mant_out),
 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 P5((xM,xMc,mant_out,exp_out,xmaxc_out),
 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 = (word)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 P4((xMc,mant,exp,xMp),
 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;

 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 = (word)GSM_MULT_R( temp1, temp );
 temp = GSM_ADD( temp, temp3 );
 *xMp++ = gsm_asr( temp, temp2 );
 }
}

/* 4.2.17 */

static void RPE_grid_positioning P3((Mc,xMp,ep),
 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 P5((S,e,xmaxc,Mc,xMc),

 struct gsm_state * S,

 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 P5((S, xmaxcr, Mcr, xMcr, erp),
 struct gsm_state * S,

 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 );

}