crypto/bn/bn_sub.c

   1 /* crypto/bn/bn_sub.c */
   2 /* Copyright (C) 1995-1997 Eric Young (eay@cryptsoft.com)
   3  * All rights reserved.
   4  *
   5  * This package is an SSL implementation written
   6  * by Eric Young (eay@cryptsoft.com).
   7  * The implementation was written so as to conform with Netscapes SSL.
   8  *
   9  * This library is free for commercial and non-commercial use as long as
  10  * the following conditions are aheared to.  The following conditions
  11  * apply to all code found in this distribution, be it the RC4, RSA,
  12  * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
  13  * included with this distribution is covered by the same copyright terms
  14  * except that the holder is Tim Hudson (tjh@cryptsoft.com).
  15  *
  16  * Copyright remains Eric Young's, and as such any Copyright notices in
  17  * the code are not to be removed.
  18  * If this package is used in a product, Eric Young should be given attribution
  19  * as the author of the parts of the library used.
  20  * This can be in the form of a textual message at program startup or
  21  * in documentation (online or textual) provided with the package.
  22  *
  23  * Redistribution and use in source and binary forms, with or without
  24  * modification, are permitted provided that the following conditions
  25  * are met:
  26  * 1. Redistributions of source code must retain the copyright
  27  *    notice, this list of conditions and the following disclaimer.
  28  * 2. Redistributions in binary form must reproduce the above copyright
  29  *    notice, this list of conditions and the following disclaimer in the
  30  *    documentation and/or other materials provided with the distribution.
  31  * 3. All advertising materials mentioning features or use of this software
  32  *    must display the following acknowledgement:
  33  *    "This product includes cryptographic software written by
  34  *     Eric Young (eay@cryptsoft.com)"
  35  *    The word 'cryptographic' can be left out if the rouines from the library
  36  *    being used are not cryptographic related :-).
  37  * 4. If you include any Windows specific code (or a derivative thereof) from
  38  *    the apps directory (application code) you must include an acknowledgement:
  39  *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
  40  *
  41  * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
  42  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  43  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  44  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  45  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  46  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  47  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  48  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  49  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  50  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  51  * SUCH DAMAGE.
  52  *
  53  * The licence and distribution terms for any publically available version or
  54  * derivative of this code cannot be changed.  i.e. this code cannot simply be
  55  * copied and put under another distribution licence
  56  * [including the GNU Public Licence.]
  57  */
  58
  59 #include <stdio.h>
  60 #include "cryptlib.h"
  61 #include "bn_lcl.h"
  62
  63 /* unsigned subtraction of b from a, a must be larger than b. */
  64 void bn_qsub(r, a, b)
  65 BIGNUM *r;
  66 BIGNUM *a;
  67 BIGNUM *b;
  68         {
  69         int max,min;
  70         register BN_ULONG t1,t2,*ap,*bp,*rp;
  71         int i,carry;
  72 #if defined(IRIX_CC_BUG) && !defined(LINT)
  73         int dummy;
  74 #endif
  75
  76         max=a->top;
  77         min=b->top;
  78         ap=a->d;
  79         bp=b->d;
  80         rp=r->d;
  81
  82         carry=0;
  83         for (i=0; i<min; i++)
  84                 {
  85                 t1= *(ap++);
  86                 t2= *(bp++);
  87                 if (carry)
  88                         {
  89                         carry=(t1 <= t2);
  90                         t1=(t1-t2-1);
  91                         }
  92                 else
  93                         {
  94                         carry=(t1 < t2);
  95                         t1=(t1-t2);
  96                         }
  97 #if defined(IRIX_CC_BUG) && !defined(LINT)
  98                 dummy=t1;
  99 #endif
 100                 *(rp++)=t1&BN_MASK2;
 101                 }
 102         if (carry) /* subtracted */
 103                 {
 104                 while (i < max)
 105                         {
 106                         i++;
 107                         t1= *(ap++);
 108                         t2=(t1-1)&BN_MASK2;
 109                         *(rp++)=t2;
 110                         if (t1 > t2) break;
 111                         }
 112                 }
 113         memcpy(rp,ap,sizeof(*rp)*(max-i));
 114 /*      for (; i<max; i++)
 115                 *(rp++)= *(ap++);*/
 116
 117         r->top=max;
 118         bn_fix_top(r);
 119         }
 120
 121 int BN_sub(r, a, b)
 122 BIGNUM *r;
 123 BIGNUM *a;
 124 BIGNUM *b;
 125         {
 126         int max,i;
 127         int add=0,neg=0;
 128         BIGNUM *tmp;
 129
 130         /*  a -  b      a-b
 131          *  a - -b      a+b
 132          * -a -  b      -(a+b)
 133          * -a - -b      b-a
 134          */
 135         if (a->neg)
 136                 {
 137                 if (b->neg)
 138                         { tmp=a; a=b; b=tmp; }
 139                 else
 140                         { add=1; neg=1; }
 141                 }
 142         else
 143                 {
 144                 if (b->neg) { add=1; neg=0; }
 145                 }
 146
 147         if (add)
 148                 {
 149                 i=(a->top > b->top);
 150                 if (bn_expand(r,(((i)?a->top:b->top)+1)*BN_BITS2) == NULL)
 151                         return(0);
 152                 if (i)
 153                         bn_qadd(r,a,b);
 154                 else
 155                         bn_qadd(r,b,a);
 156                 r->neg=neg;
 157                 return(1);
 158                 }
 159
 160         /* We are actually doing a - b :-) */
 161
 162         max=(a->top > b->top)?a->top:b->top;
 163         if (bn_expand(r,max*BN_BITS2) == NULL) return(0);
 164         if (BN_ucmp(a,b) < 0)
 165                 {
 166                 bn_qsub(r,b,a);
 167                 r->neg=1;
 168                 }
 169         else
 170                 {
 171                 bn_qsub(r,a,b);
 172                 r->neg=0;
 173                 }
 174         return(1);
 175         }
 176