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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 <stdio.h>
#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;
      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. */
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);
      }

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);
      }


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