lpc.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"

#ifdef K6OPT
#include "k6opt.h"
#endif

#undef   P

/*
 *  4.2.4 .. 4.2.7 LPC ANALYSIS SECTION
 */

/* 4.2.4 */


static void Autocorrelation P2((s, L_ACF),
   word     * s,     /* [0..159] IN/OUT  */
   longword * L_ACF) /* [0..8]   OUT     */
/*
 *  The goal is to compute the array L_ACF[k].  The signal s[i] must
 *  be scaled in order to avoid an overflow situation.
 */
{
#ifndef K6OPT
   register int   k, i;
   word temp;
#endif

   word     smax, scalauto;

#ifdef   USE_FLOAT_MUL
   float    float_s[160];
#endif

   /*  Dynamic scaling of the array  s[0..159]
    */

   /*  Search for the maximum.
    */
#ifndef K6OPT
   smax = 0;
   for (k = 0; k <= 159; k++) {
      temp = GSM_ABS( s[k] );
      if (temp > smax) smax = temp;
   }
#else
   {
      longword lmax;
      lmax = k6maxmin(s,160,NULL);
      smax = (lmax > MAX_WORD) ? MAX_WORD : lmax;
   }
#endif
   /*  Computation of the scaling factor.
    */
   if (smax == 0) scalauto = 0;
   else {
      assert(smax > 0);
      scalauto = 4 - gsm_norm( (longword)smax << 16 );/* sub(4,..) */
   }

   /*  Scaling of the array s[0...159]
    */

   if (scalauto > 0) {
#  ifndef K6OPT

# ifdef USE_FLOAT_MUL
#   define SCALE(n)  \
   case n: for (k = 0; k <= 159; k++) \
         float_s[k] = (float) \
            (s[k] = GSM_MULT_R(s[k], 16384 >> (n-1)));\
      break;
# else
#   define SCALE(n)  \
   case n: for (k = 0; k <= 159; k++) \
         s[k] = (word)GSM_MULT_R( s[k], 16384 >> (n-1) );\
      break;
# endif /* USE_FLOAT_MUL */

      switch (scalauto) {
      SCALE(1)
      SCALE(2)
      SCALE(3)
      SCALE(4)
      }
# undef  SCALE

#  else /* K6OPT */
      k6vsraw(s,160,scalauto);
#  endif
   }
# ifdef  USE_FLOAT_MUL
   else for (k = 0; k <= 159; k++) float_s[k] = (float) s[k];
# endif

   /*  Compute the L_ACF[..].
    */
#ifndef K6OPT
   {
# ifdef  USE_FLOAT_MUL
      register float * sp = float_s;
      register float   sl = *sp;

#     define STEP(k)  L_ACF[k] += (longword)(sl * sp[ -(k) ]);
# else
      word  * sp = s;
      word    sl = *sp;

#     define STEP(k)  L_ACF[k] += ((longword)sl * sp[ -(k) ]);
# endif

#  define NEXTI    sl = *++sp


   for (k = 9; k--; L_ACF[k] = 0) ;

   STEP (0);
   NEXTI;
   STEP(0); STEP(1);
   NEXTI;
   STEP(0); STEP(1); STEP(2);
   NEXTI;
   STEP(0); STEP(1); STEP(2); STEP(3);
   NEXTI;
   STEP(0); STEP(1); STEP(2); STEP(3); STEP(4);
   NEXTI;
   STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5);
   NEXTI;
   STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6);
   NEXTI;
   STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6); STEP(7);

   for (i = 8; i <= 159; i++) {

      NEXTI;

      STEP(0);
      STEP(1); STEP(2); STEP(3); STEP(4);
      STEP(5); STEP(6); STEP(7); STEP(8);
   }

   for (k = 9; k--; L_ACF[k] <<= 1) ;

   }

#else
   {
      int k;
      for (k=0; k<9; k++) {
         L_ACF[k] = 2*k6iprod(s,s+k,160-k);
      }
   }
#endif
   /*   Rescaling of the array s[0..159]
    */
   if (scalauto > 0) {
      assert(scalauto <= 4);
#ifndef K6OPT
      for (k = 160; k--; *s++ <<= scalauto) ;
#  else /* K6OPT */
      k6vsllw(s,160,scalauto);
#  endif
   }
}

#if defined(USE_FLOAT_MUL) && defined(FAST)

static void Fast_Autocorrelation P2((s, L_ACF),
   word * s,      /* [0..159] IN/OUT  */
   longword * L_ACF) /* [0..8]   OUT     */
{
   register int   k, i;
   float f_L_ACF[9];
   float scale;

   float          s_f[160];
   register float *sf = s_f;

   for (i = 0; i < 160; ++i) sf[i] = s[i];
   for (k = 0; k <= 8; k++) {
      register float L_temp2 = 0;
      register float *sfl = sf - k;
      for (i = k; i < 160; ++i) L_temp2 += sf[i] * sfl[i];
      f_L_ACF[k] = L_temp2;
   }
   scale = MAX_LONGWORD / f_L_ACF[0];

   for (k = 0; k <= 8; k++) {
      L_ACF[k] = f_L_ACF[k] * scale;
   }
}
#endif   /* defined (USE_FLOAT_MUL) && defined (FAST) */

/* 4.2.5 */

static void Reflection_coefficients P2( (L_ACF, r),
   longword * L_ACF,    /* 0...8 IN */
   register word  * r         /* 0...7 OUT   */
)
{
   register int   i, m, n;
   register word  temp;
   word     ACF[9];  /* 0..8 */
   word     P[  9];  /* 0..8 */
   word     K[  9]; /* 2..8 */

   /*  Schur recursion with 16 bits arithmetic.
    */

   if (L_ACF[0] == 0) {
      for (i = 8; i--; *r++ = 0) ;
      return;
   }

   assert( L_ACF[0] != 0 );
   temp = gsm_norm( L_ACF[0] );

   assert(temp >= 0 && temp < 32);

   /* ? overflow ? */
   for (i = 0; i <= 8; i++) ACF[i] = (word)SASR( L_ACF[i] << temp, 16 );

   /*   Initialize array P[..] and K[..] for the recursion.
    */

   for (i = 1; i <= 7; i++) K[ i ] = ACF[ i ];
   for (i = 0; i <= 8; i++) P[ i ] = ACF[ i ];

   /*   Compute reflection coefficients
    */
   for (n = 1; n <= 8; n++, r++) {

      temp = P[1];
      temp = GSM_ABS(temp);
      if (P[0] < temp) {
         for (i = n; i <= 8; i++) *r++ = 0;
         return;
      }

      *r = gsm_div( temp, P[0] );

      assert(*r >= 0);
      if (P[1] > 0) *r = -*r;    /* r[n] = sub(0, r[n]) */
      assert (*r != MIN_WORD);
      if (n == 8) return;

      /*  Schur recursion
       */
      temp = (word)GSM_MULT_R( P[1], *r );
      P[0] = GSM_ADD( P[0], temp );

      for (m = 1; m <= 8 - n; m++) {
         temp     = (word)GSM_MULT_R( K[ m   ],    *r );
         P[m]     = GSM_ADD(    P[ m+1 ],  temp );

         temp     = (word)GSM_MULT_R( P[ m+1 ],    *r );
         K[m]     = GSM_ADD(    K[ m   ],  temp );
      }
   }
}

/* 4.2.6 */

static void Transformation_to_Log_Area_Ratios P1((r),
   register word  * r         /* 0..7     IN/OUT */
)
/*
 *  The following scaling for r[..] and LAR[..] has been used:
 *
 *  r[..]   = integer( real_r[..]*32768. ); -1 <= real_r < 1.
 *  LAR[..] = integer( real_LAR[..] * 16384 );
 *  with -1.625 <= real_LAR <= 1.625
 */
{
   register word  temp;
   register int   i;


   /* Computation of the LAR[0..7] from the r[0..7]
    */
   for (i = 1; i <= 8; i++, r++) {

      temp = *r;
      temp = GSM_ABS(temp);
      assert(temp >= 0);

      if (temp < 22118) {
         temp >>= 1;
      } else if (temp < 31130) {
         assert( temp >= 11059 );
         temp -= 11059;
      } else {
         assert( temp >= 26112 );
         temp -= 26112;
         temp <<= 2;
      }

      *r = *r < 0 ? -temp : temp;
      assert( *r != MIN_WORD );
   }
}

/* 4.2.7 */

static void Quantization_and_coding P1((LAR),
   register word * LAR     /* [0..7]   IN/OUT   */
)
{
   register word  temp;


   /*  This procedure needs four tables; the following equations
    *  give the optimum scaling for the constants:
    *
    *  A[0..7] = integer( real_A[0..7] * 1024 )
    *  B[0..7] = integer( real_B[0..7] *  512 )
    *  MAC[0..7] = maximum of the LARc[0..7]
    *  MIC[0..7] = minimum of the LARc[0..7]
    */

#  undef STEP
#  define   STEP( A, B, MAC, MIC )     \
      temp = (word)GSM_MULT( A,   *LAR ); \
      temp = GSM_ADD(  temp,   B ); \
      temp = GSM_ADD(  temp, 256 ); \
      temp = (word)SASR(     temp,   9 ); \
      *LAR  =  temp>MAC ? MAC - MIC : (temp<MIC ? 0 : temp - MIC); \
      LAR++;

   STEP(  20480,     0,  31, -32 );
   STEP(  20480,     0,  31, -32 );
   STEP(  20480,  2048,  15, -16 );
   STEP(  20480, -2560,  15, -16 );

   STEP(  13964,    94,   7,  -8 );
   STEP(  15360, -1792,   7,  -8 );
   STEP(   8534,  -341,   3,  -4 );
   STEP(   9036, -1144,   3,  -4 );

#  undef STEP
}

void Gsm_LPC_Analysis P3((S, s,LARc),
   struct gsm_state *S,
   word      * s,    /* 0..159 signals IN/OUT   */
        word       * LARc) /* 0..7   LARc's  OUT   */
{
   longword L_ACF[9];

#if defined(USE_FLOAT_MUL) && defined(FAST)
   if (S->fast) Fast_Autocorrelation (s,    L_ACF );
   else
#endif
   Autocorrelation           (s,   L_ACF  );
   Reflection_coefficients      (L_ACF, LARc );
   Transformation_to_Log_Area_Ratios (LARc);
   Quantization_and_coding      (LARc);
}