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] =  (  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 = 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;
        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 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 );

}

---