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;
}