bn_add.c

/* crypto/bn/bn_add.c */
/* Copyright (C) 1995-1998 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 "cryptlib.h"
#include "bn_lcl.h"

/* r can == a or b */
int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
	{
	const BIGNUM *tmp;
	int a_neg = a->neg, ret;

	bn_check_top(a);
	bn_check_top(b);

	/*  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_ucmp(a,b) < 0)
			{
			if (!BN_usub(r,b,a)) return(0);
			r->neg=1;
			}
		else
			{
			if (!BN_usub(r,a,b)) return(0);
			r->neg=0;
			}
		return(1);
		}

	ret = BN_uadd(r,a,b);
	r->neg = a_neg;
	bn_check_top(r);
	return ret;
	}

/* unsigned add of b to a */
int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
	{
	int max,min,dif;
	const BN_ULONG *ap,*bp;
	BN_ULONG *rp,carry,t1,t2;
	const BIGNUM *tmp;

	bn_check_top(a);
	bn_check_top(b);

	if (a->top < b->top)
		{ tmp=a; a=b; b=tmp; }
	max = a->top;
	min = b->top;
	dif = max - min;

	if (bn_wexpand(r,max+1) == NULL)
		return 0;

	r->top=max;


	ap=a->d;
	bp=b->d;
	rp=r->d;

	carry=bn_add_words(rp,ap,bp,min);
	rp+=min;
	ap+=min;
	bp+=min;

	if (carry)
		{
		while (dif)
			{
			dif--;
			t1 = *(ap++);
			t2 = (t1+1) & BN_MASK2;
			*(rp++) = t2;
			if (t2)
				{
				carry=0;
				break;
				}
			}
		if (carry)
			{
			/* carry != 0 => dif == 0 */
			*rp = 1;
			r->top++;
			}
		}
	if (dif && rp != ap)
		while (dif--)
			/* copy remaining words if ap != rp */
			*(rp++) = *(ap++);
	r->neg = 0;
	bn_check_top(r);
	return 1;
	}

/* unsigned subtraction of b from a, a must be larger than b. */
int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
	{
	int max,min,dif;
	register BN_ULONG t1,t2,*rp;
	register const BN_ULONG *ap,*bp;
	int i,carry;

	bn_check_top(a);
	bn_check_top(b);

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

	if (dif < 0)	/* hmm... should not be happening */
		{
		BNerr(BN_F_BN_USUB,BN_R_ARG2_LT_ARG3);
		return(0);
		}

	if (bn_wexpand(r,max) == NULL) return(0);

	ap=a->d;
	bp=b->d;
	rp=r->d;

#if 1
	carry=0;
	for (i = min; i != 0; i--)
		{
		t1= *(ap++);
		t2= *(bp++);
		if (carry)
			{
			carry=(t1 <= t2);
			t1=(t1-t2-1)&BN_MASK2;
			}
		else
			{
			carry=(t1 < t2);
			t1=(t1-t2)&BN_MASK2;
			}
		*(rp++)=t1&BN_MASK2;
		}
#else
	carry=bn_sub_words(rp,ap,bp,min);
	ap+=min;
	bp+=min;
	rp+=min;
#endif
	if (carry) /* subtracted */
		{
		if (!dif)
			/* error: a < b */
			return 0;
		while (dif)
			{
			dif--;
			t1 = *(ap++);
			t2 = (t1-1)&BN_MASK2;
			*(rp++) = t2;
			if (t1)
				break;
			}
		}
#if 0
	memcpy(rp,ap,sizeof(*rp)*(max-i));
#else
	if (rp != ap)
		{
		for (;;)
			{
			if (!dif--) break;
			rp[0]=ap[0];
			if (!dif--) break;
			rp[1]=ap[1];
			if (!dif--) break;
			rp[2]=ap[2];
			if (!dif--) break;
			rp[3]=ap[3];
			rp+=4;
			ap+=4;
			}
		}
#endif

	r->top=max;
	r->neg=0;
	bn_correct_top(r);
	return(1);
	}

int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
	{
	int max;
	int add=0,neg=0;
	const BIGNUM *tmp;

	bn_check_top(a);
	bn_check_top(b);

	/*  a -  b	a-b
	 *  a - -b	a+b
	 * -a -  b	-(a+b)
	 * -a - -b	b-a
	 */
	if (a->neg)
		{
		if (b->neg)
			{ tmp=a; a=b; b=tmp; }
		else
			{ add=1; neg=1; }
		}
	else
		{
		if (b->neg) { add=1; neg=0; }
		}

	if (add)
		{
		if (!BN_uadd(r,a,b)) return(0);
		r->neg=neg;
		return(1);
		}

	/* We are actually doing a - b :-) */

	max=(a->top > b->top)?a->top:b->top;
	if (bn_wexpand(r,max) == NULL) return(0);
	if (BN_ucmp(a,b) < 0)
		{
		if (!BN_usub(r,b,a)) return(0);
		r->neg=1;
		}
	else
		{
		if (!BN_usub(r,a,b)) return(0);
		r->neg=0;
		}
	bn_check_top(r);
	return(1);
	}