add.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.
 */

/* $Header$ */

/*
 *  See private.h for the more commonly used macro versions.
 */

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

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

#define  saturate(x)    \
   ((x) < MIN_WORD ? MIN_WORD : (x) > MAX_WORD ? MAX_WORD: (x))

word gsm_add P2((a,b), word a, word b)
{
   longword sum = (longword)a + (longword)b;
   return (word)saturate(sum);
}

word gsm_sub P2((a,b), word a, word b)
{
   longword diff = (longword)a - (longword)b;
   return (word)saturate(diff);
}

word gsm_mult P2((a,b), word a, word b)
{
   if (a == MIN_WORD && b == MIN_WORD) return MAX_WORD;
   else return (word)SASR( (longword)a * (longword)b, 15 );
}

word gsm_mult_r P2((a,b), word a, word b)
{
   if (b == MIN_WORD && a == MIN_WORD) return MAX_WORD;
   else {
      longword prod = (longword)a * (longword)b + 16384;
      prod >>= 15;
      return (word)(prod & 0xFFFF);
   }
}

word gsm_abs P1((a), word a)
{
   return a < 0 ? (a == MIN_WORD ? MAX_WORD : -a) : a;
}

longword gsm_L_mult P2((a,b),word a, word b)
{
   assert( a != MIN_WORD || b != MIN_WORD );
   return ((longword)a * (longword)b) << 1;
}

longword gsm_L_add P2((a,b), longword a, longword b)
{
   if (a < 0) {
      if (b >= 0) return a + b;
      else {
         ulongword A = (ulongword)-(a + 1) + (ulongword)-(b + 1);
         return A >= MAX_LONGWORD ? MIN_LONGWORD :-(longword)A-2;
      }
   }
   else if (b <= 0) return a + b;
   else {
      ulongword A = (ulongword)a + (ulongword)b;
      return A > MAX_LONGWORD ? MAX_LONGWORD : A;
   }
}

longword gsm_L_sub P2((a,b), longword a, longword b)
{
   if (a >= 0) {
      if (b >= 0) return a - b;
      else {
         /* a>=0, b<0 */

         ulongword A = (ulongword)a + -(b + 1);
         return A >= MAX_LONGWORD ? MAX_LONGWORD : (A + 1);
      }
   }
   else if (b <= 0) return a - b;
   else {
      /* a<0, b>0 */

      ulongword A = (ulongword)-(a + 1) + b;
      return A >= MAX_LONGWORD ? MIN_LONGWORD : -(longword)A - 1;
   }
}

static unsigned char const bitoff[ 256 ] = {
    8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
    3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};

word gsm_norm P1((a), longword a )
/*
 * the number of left shifts needed to normalize the 32 bit
 * variable L_var1 for positive values on the interval
 *
 * with minimum of
 * minimum of 1073741824  (01000000000000000000000000000000) and
 * maximum of 2147483647  (01111111111111111111111111111111)
 *
 *
 * and for negative values on the interval with
 * minimum of -2147483648 (-10000000000000000000000000000000) and
 * maximum of -1073741824 ( -1000000000000000000000000000000).
 *
 * in order to normalize the result, the following
 * operation must be done: L_norm_var1 = L_var1 << norm( L_var1 );
 *
 * (That's 'ffs', only from the left, not the right..)
 */
{
   assert(a != 0);

   if (a < 0) {
      if (a <= -1073741824) return 0;
      a = ~a;
   }

   return    a & 0xffff0000
      ? ( a & 0xff000000
        ?  -1 + bitoff[ 0xFF & (a >> 24) ]
        :   7 + bitoff[ 0xFF & (a >> 16) ] )
      : ( a & 0xff00
        ?  15 + bitoff[ 0xFF & (a >> 8) ]
        :  23 + bitoff[ 0xFF & a ] );
}

longword gsm_L_asl P2((a,n), longword a, int n)
{
   if (n >= 32) return 0;
   if (n <= -32) return -(a < 0);
   if (n < 0) return gsm_L_asr(a, -n);
   return a << n;
}

word gsm_asl P2((a,n), word a, int n)
{
   if (n >= 16) return 0;
   if (n <= -16) return -(a < 0);
   if (n < 0) return gsm_asr(a, -n);
   return a << n;
}

longword gsm_L_asr P2((a,n), longword a, int n)
{
   if (n >= 32) return -(a < 0);
   if (n <= -32) return 0;
   if (n < 0) return a << -n;

#  ifdef SASR
      return a >> n;
#  else
      if (a >= 0) return a >> n;
      else return -(longword)( -(ulongword)a >> n );
#  endif
}

word gsm_asr P2((a,n), word a, int n)
{
   if (n >= 16) return -(a < 0);
   if (n <= -16) return 0;
   if (n < 0) return a << -n;

#  ifdef SASR
      return a >> n;
#  else
      if (a >= 0) return a >> n;
      else return -(word)( -(uword)a >> n );
#  endif
}

/*
 *  (From p. 46, end of section 4.2.5)
 *
 *  NOTE: The following lines gives [sic] one correct implementation
 *      of the div(num, denum) arithmetic operation.  Compute div
 *        which is the integer division of num by denum: with denum
 *   >= num > 0
 */

word gsm_div P2((num,denum), word num, word denum)
{
   longword L_num   = num;
   longword L_denum = denum;
   word     div   = 0;
   int      k  = 15;

   /* The parameter num sometimes becomes zero.
    * Although this is explicitly guarded against in 4.2.5,
    * we assume that the result should then be zero as well.
    */

   /* assert(num != 0); */

   assert(num >= 0 && denum >= num);
   if (num == 0)
       return 0;

   while (k--) {
      div   <<= 1;
      L_num <<= 1;

      if (L_num >= L_denum) {
         L_num -= L_denum;
         div++;
      }
   }

   return div;
}