Logo Search packages:      
Sourcecode: libgsm version File versions  Download package

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.
 */

/* $Header: /tmp_amd/presto/export/kbs/jutta/src/gsm/RCS/rpe.c,v 1.3 1994/05/10 20:18:46 jutta Exp $ */

#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 */

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 ));
      }
}

/* 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 );

}

Generated by  Doxygen 1.6.0   Back to index