openssl/crypto/bn/bn_add.c

/* crypto/bn/bn_add.c */
/* Copyright (C) 1995-1997 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>
#include "cryptlib.h"
#include "bn_lcl.h"

/* r can == a or b */
int BN_add(r, a, b)
BIGNUM *r;
BIGNUM *a;
BIGNUM *b;
	{
	int i;
	BIGNUM *tmp;

	/*  a +  b	a+b
	 *  a + -b	a-b
	 * -a +  b	b-a
	 * -a + -b	-(a+b)
	 */
	if (a->neg ^ b->neg)
		{
		/* only one is negative */
		if (a->neg)
			{ tmp=a; a=b; b=tmp; }

		/* we are now a - b */
		if (bn_expand(r,((a->top > b->top)?a->top:b->top)*BN_BITS2)
			== NULL) return(0);

		if (BN_ucmp(a,b) < 0)
			{
			bn_qsub(r,b,a);
			r->neg=1;
			}
		else
			{
			bn_qsub(r,a,b);
			r->neg=0;
			}
		return(1);
		}

	if (a->neg) /* both are neg */
		r->neg=1;
	else
		r->neg=0;

	i=(a->top > b->top);
	if (bn_expand(r,(((i)?a->top:b->top)+1)*BN_BITS2) == NULL) return(0);

	if (i)
		bn_qadd(r,a,b);
	else
		bn_qadd(r,b,a);
	return(1);
	}

/* unsigned add of b to a, r must be large enough */
void bn_qadd(r,a,b)
BIGNUM *r;
BIGNUM *a;
BIGNUM *b;
	{
	register int i;
	int max,min;
	BN_ULONG *ap,*bp,*rp,carry,t1,t2;

	max=a->top;
	min=b->top;
	r->top=max;

	ap=a->d;
	bp=b->d;
	rp=r->d;
	carry=0;
	for (i=0; i<min; i++)
		{
		t1= *(ap++);
		t2= *(bp++);
		if (carry)
			{
			carry=(t2 >= ((~t1)&BN_MASK2));
			t2=(t1+t2+1)&BN_MASK2;
			}
		else
			{
			t2=(t1+t2)&BN_MASK2;
			carry=(t2 < t1);
			}
		*(rp++)=t2;
		}
	if (carry)
		{
		while (i < max)
			{
			t1= *(ap++);
			t2=(t1+1)&BN_MASK2;
			*(rp++)=t2;
			carry=(t2 < t1);
			i++;
			if (!carry) break;
			}
		if ((i >= max) && carry)
			{
			*(rp++)=1;
			r->top++;
			}
		}
	for (; i<max; i++)
		*(rp++)= *(ap++);
	/* memcpy(rp,ap,sizeof(*ap)*(max-i));*/
	}