crypto/bn/bn_add.c

   1 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   2  * All rights reserved.
   3  *
   4  * This package is an SSL implementation written
   5  * by Eric Young (eay@cryptsoft.com).
   6  * The implementation was written so as to conform with Netscapes SSL.
   7  *
   8  * This library is free for commercial and non-commercial use as long as
   9  * the following conditions are aheared to.  The following conditions
  10  * apply to all code found in this distribution, be it the RC4, RSA,
  11  * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
  12  * included with this distribution is covered by the same copyright terms
  13  * except that the holder is Tim Hudson (tjh@cryptsoft.com).
  14  *
  15  * Copyright remains Eric Young's, and as such any Copyright notices in
  16  * the code are not to be removed.
  17  * If this package is used in a product, Eric Young should be given attribution
  18  * as the author of the parts of the library used.
  19  * This can be in the form of a textual message at program startup or
  20  * in documentation (online or textual) provided with the package.
  21  *
  22  * Redistribution and use in source and binary forms, with or without
  23  * modification, are permitted provided that the following conditions
  24  * are met:
  25  * 1. Redistributions of source code must retain the copyright
  26  *    notice, this list of conditions and the following disclaimer.
  27  * 2. Redistributions in binary form must reproduce the above copyright
  28  *    notice, this list of conditions and the following disclaimer in the
  29  *    documentation and/or other materials provided with the distribution.
  30  * 3. All advertising materials mentioning features or use of this software
  31  *    must display the following acknowledgement:
  32  *    "This product includes cryptographic software written by
  33  *     Eric Young (eay@cryptsoft.com)"
  34  *    The word 'cryptographic' can be left out if the rouines from the library
  35  *    being used are not cryptographic related :-).
  36  * 4. If you include any Windows specific code (or a derivative thereof) from
  37  *    the apps directory (application code) you must include an acknowledgement:
  38  *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
  39  *
  40  * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
  41  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  42  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  43  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  44  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  45  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  46  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  47  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  48  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  49  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  50  * SUCH DAMAGE.
  51  *
  52  * The licence and distribution terms for any publically available version or
  53  * derivative of this code cannot be changed.  i.e. this code cannot simply be
  54  * copied and put under another distribution licence
  55  * [including the GNU Public Licence.]
  56  */
  57
  58 #include "internal/cryptlib.h"
  59 #include "bn_lcl.h"
  60
  61 /* r can == a or b */
  62 int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
  63 {
  64     const BIGNUM *tmp;
  65     int a_neg = a->neg, ret;
  66
  67     bn_check_top(a);
  68     bn_check_top(b);
  69
  70     /*-
  71      *  a +  b      a+b
  72      *  a + -b      a-b
  73      * -a +  b      b-a
  74      * -a + -b      -(a+b)
  75      */
  76     if (a_neg ^ b->neg) {
  77         /* only one is negative */
  78         if (a_neg) {
  79             tmp = a;
  80             a = b;
  81             b = tmp;
  82         }
  83
  84         /* we are now a - b */
  85
  86         if (BN_ucmp(a, b) < 0) {
  87             if (!BN_usub(r, b, a))
  88                 return (0);
  89             r->neg = 1;
  90         } else {
  91             if (!BN_usub(r, a, b))
  92                 return (0);
  93             r->neg = 0;
  94         }
  95         return (1);
  96     }
  97
  98     ret = BN_uadd(r, a, b);
  99     r->neg = a_neg;
 100     bn_check_top(r);
 101     return ret;
 102 }
 103
 104 /* unsigned add of b to a */
 105 int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
 106 {
 107     int max, min, dif;
 108     const BN_ULONG *ap, *bp;
 109     BN_ULONG *rp, carry, t1, t2;
 110     const BIGNUM *tmp;
 111
 112     bn_check_top(a);
 113     bn_check_top(b);
 114
 115     if (a->top < b->top) {
 116         tmp = a;
 117         a = b;
 118         b = tmp;
 119     }
 120     max = a->top;
 121     min = b->top;
 122     dif = max - min;
 123
 124     if (bn_wexpand(r, max + 1) == NULL)
 125         return 0;
 126
 127     r->top = max;
 128
 129     ap = a->d;
 130     bp = b->d;
 131     rp = r->d;
 132
 133     carry = bn_add_words(rp, ap, bp, min);
 134     rp += min;
 135     ap += min;
 136     bp += min;
 137
 138     if (carry) {
 139         while (dif) {
 140             dif--;
 141             t1 = *(ap++);
 142             t2 = (t1 + 1) & BN_MASK2;
 143             *(rp++) = t2;
 144             if (t2) {
 145                 carry = 0;
 146                 break;
 147             }
 148         }
 149         if (carry) {
 150             /* carry != 0 => dif == 0 */
 151             *rp = 1;
 152             r->top++;
 153         }
 154     }
 155     if (dif && rp != ap)
 156         while (dif--)
 157             /* copy remaining words if ap != rp */
 158             *(rp++) = *(ap++);
 159     r->neg = 0;
 160     bn_check_top(r);
 161     return 1;
 162 }
 163
 164 /* unsigned subtraction of b from a, a must be larger than b. */
 165 int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
 166 {
 167     int max, min, dif;
 168     register BN_ULONG t1, t2, *rp;
 169     register const BN_ULONG *ap, *bp;
 170     int i, carry;
 171
 172     bn_check_top(a);
 173     bn_check_top(b);
 174
 175     max = a->top;
 176     min = b->top;
 177     dif = max - min;
 178
 179     if (dif < 0) {              /* hmm... should not be happening */
 180         BNerr(BN_F_BN_USUB, BN_R_ARG2_LT_ARG3);
 181         return (0);
 182     }
 183
 184     if (bn_wexpand(r, max) == NULL)
 185         return (0);
 186
 187     ap = a->d;
 188     bp = b->d;
 189     rp = r->d;
 190
 191 #if 1
 192     carry = 0;
 193     for (i = min; i != 0; i--) {
 194         t1 = *(ap++);
 195         t2 = *(bp++);
 196         if (carry) {
 197             carry = (t1 <= t2);
 198             t1 = (t1 - t2 - 1) & BN_MASK2;
 199         } else {
 200             carry = (t1 < t2);
 201             t1 = (t1 - t2) & BN_MASK2;
 202         }
 203         *(rp++) = t1 & BN_MASK2;
 204     }
 205 #else
 206     carry = bn_sub_words(rp, ap, bp, min);
 207     ap += min;
 208     bp += min;
 209     rp += min;
 210 #endif
 211     if (carry) {                /* subtracted */
 212         if (!dif)
 213             /* error: a < b */
 214             return 0;
 215         while (dif) {
 216             dif--;
 217             t1 = *(ap++);
 218             t2 = (t1 - 1) & BN_MASK2;
 219             *(rp++) = t2;
 220             if (t1)
 221                 break;
 222         }
 223     }
 224     if (dif && ap != rp)
 225         memcpy(rp, ap, sizeof(*rp) * dif);
 226
 227     r->top = max;
 228     r->neg = 0;
 229     bn_correct_top(r);
 230     return (1);
 231 }
 232
 233 int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
 234 {
 235     int max;
 236     int add = 0, neg = 0;
 237     const BIGNUM *tmp;
 238
 239     bn_check_top(a);
 240     bn_check_top(b);
 241
 242     /*-
 243      *  a -  b      a-b
 244      *  a - -b      a+b
 245      * -a -  b      -(a+b)
 246      * -a - -b      b-a
 247      */
 248     if (a->neg) {
 249         if (b->neg) {
 250             tmp = a;
 251             a = b;
 252             b = tmp;
 253         } else {
 254             add = 1;
 255             neg = 1;
 256         }
 257     } else {
 258         if (b->neg) {
 259             add = 1;
 260             neg = 0;
 261         }
 262     }
 263
 264     if (add) {
 265         if (!BN_uadd(r, a, b))
 266             return (0);
 267         r->neg = neg;
 268         return (1);
 269     }
 270
 271     /* We are actually doing a - b :-) */
 272
 273     max = (a->top > b->top) ? a->top : b->top;
 274     if (bn_wexpand(r, max) == NULL)
 275         return (0);
 276     if (BN_ucmp(a, b) < 0) {
 277         if (!BN_usub(r, b, a))
 278             return (0);
 279         r->neg = 1;
 280     } else {
 281         if (!BN_usub(r, a, b))
 282             return (0);
 283         r->neg = 0;
 284     }
 285     bn_check_top(r);
 286     return (1);
 287 }