/* 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);

 	}