/* $OpenBSD: bn_add.c,v 1.13 2018/07/23 18:07:21 tb Exp $ */

/* 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 <openssl/err.h>

#include "bn_lcl.h"

int

BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)

{

  int ret, r_neg;

  bn_check_top(a);

  bn_check_top(b);

  if (a->neg == b->neg) {

    r_neg = a->neg;

    ret = BN_uadd(r, a, b);

  } else {

    int cmp = BN_ucmp(a, b);

    if (cmp > 0) {

      r_neg = a->neg;

      ret = BN_usub(r, a, b);

    } else if (cmp < 0) {

      r_neg = b->neg;

      ret = BN_usub(r, b, a);

    } else {

      r_neg = 0;

      BN_zero(r);

      ret = 1;

    }

  }

  r->neg = r_neg;

  bn_check_top(r);

  return ret;

}

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;

  bn_check_top(a);

  bn_check_top(b);

  if (a->top < b->top) {

    const BIGNUM *tmp;

    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;

  while (dif) {

    dif--;

    t1 = *(ap++);

    t2 = (t1 + carry) & BN_MASK2;

    *(rp++) = t2;

    carry &= (t2 == 0);

  }

  *rp = carry;

  r->top += carry;

  r->neg = 0;

  bn_check_top(r);

  return 1;

}

int

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

{

  int max, min, dif;

  const BN_ULONG *ap, *bp;

  BN_ULONG t1, t2, borrow, *rp;

  bn_check_top(a);

  bn_check_top(b);

  max = a->top;

  min = b->top;

  dif = max - min;

  if (dif < 0) {

    BNerror(BN_R_ARG2_LT_ARG3);

    return 0;

  }

  if (bn_wexpand(r, max) == NULL)

    return 0;

  ap = a->d;

  bp = b->d;

  rp = r->d;

  borrow = bn_sub_words(rp, ap, bp, min);

  ap += min;

  rp += min;

  while (dif) {

    dif--;

    t1 = *(ap++);

    t2 = (t1 - borrow) & BN_MASK2;

    *(rp++) = t2;

    borrow &= (t1 == 0);

  }

  while (max > 0 && *--rp == 0)

    max--;

  r->top = max;

  r->neg = 0;

  bn_correct_top(r);

  return 1;

}

int

BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)

{

  int ret, r_neg;

  bn_check_top(a);

  bn_check_top(b);

  if (a->neg != b->neg) {

    r_neg = a->neg;

    ret = BN_uadd(r, a, b);

  } else {

    int cmp = BN_ucmp(a, b);

    if (cmp > 0) {

      r_neg = a->neg;

      ret = BN_usub(r, a, b);

    } else if (cmp < 0) {

      r_neg = !b->neg;

      ret = BN_usub(r, b, a);

    } else {

      r_neg = 0;

      BN_zero(r);

      ret = 1;

    }

  }

  r->neg = r_neg;

  bn_check_top(r);

  return ret;

}