/* 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 <stdio.h>

#include "cryptlib.h"

#include "bn_lcl.h"

/* r can == a or b */

EXPORT_C 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 */

EXPORT_C int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)

	{

	int max,min,dif;

	BN_ULONG *ap,*bp,*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. */

EXPORT_C int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)

	{

	int max,min,dif;

	register BN_ULONG t1,t2,*ap,*bp,*rp;

	int i,carry;

#if defined(IRIX_CC_BUG) && !defined(LINT)

	int dummy;

#endif

	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;

			}

#if defined(IRIX_CC_BUG) && !defined(LINT)

		dummy=t1;

#endif

		*(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);

	}

EXPORT_C 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);

	}