add.c

IP网络语音通讯软件源代码. 不可多得的语音源代码

/*
 * 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: n:\\development/speak_freely/GSM/ADD.C,v 1.1.1.1 1998/10/15 00:47:38 Administrator Exp $ */

/*
 *	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 = a + b;
		return (word) saturate(sum);
}

word gsm_sub P2((a,b), word a, word b)
{
		longword diff = a - 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 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_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
}

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_asr((word) 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;
}

/* 
 *	(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;
}