add.c

Go to the documentation of this file.

/*
 * 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 saturate(sum);
}

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

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

---