lib/libcrypto/bn/bn_add.c

   1 /* $OpenBSD: bn_add.c,v 1.11 2017/01/29 17:49:22 beck Exp $ */
   2 /* Copyright (C) 1995-1998 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
  61 #include <openssl/err.h>
  62
  63 #include "bn_lcl.h"
  64
  65 /* r can == a or b */
  66 int
  67 BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
  68 {
  69         const BIGNUM *tmp;
  70         int a_neg = a->neg, ret;
  71
  72         bn_check_top(a);
  73         bn_check_top(b);
  74
  75         /*  a +  b      a+b
  76          *  a + -b      a-b
  77          * -a +  b      b-a
  78          * -a + -b      -(a+b)
  79          */
  80         if (a_neg ^ b->neg) {
  81                 /* only one is negative */
  82                 if (a_neg)
  83                                 { tmp = a;
  84                         a = b;
  85                         b = tmp;
  86                 }
  87
  88                 /* we are now a - b */
  89
  90                 if (BN_ucmp(a, b) < 0) {
  91                         if (!BN_usub(r, b, a))
  92                                 return (0);
  93                         r->neg = 1;
  94                 } else {
  95                         if (!BN_usub(r, a, b))
  96                                 return (0);
  97                         r->neg = 0;
  98                 }
  99                 return (1);
 100         }
 101
 102         ret = BN_uadd(r, a, b);
 103         r->neg = a_neg;
 104         bn_check_top(r);
 105         return ret;
 106 }
 107
 108 /* unsigned add of b to a */
 109 int
 110 BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
 111 {
 112         int max, min, dif;
 113         BN_ULONG *ap, *bp, *rp, carry, t1, t2;
 114         const BIGNUM *tmp;
 115
 116         bn_check_top(a);
 117         bn_check_top(b);
 118
 119         if (a->top < b->top) {
 120                 tmp = a;
 121                 a = b;
 122                 b = tmp;
 123         }
 124         max = a->top;
 125         min = b->top;
 126         dif = max - min;
 127
 128         if (bn_wexpand(r, max + 1) == NULL)
 129                 return 0;
 130
 131         r->top = max;
 132
 133         ap = a->d;
 134         bp = b->d;
 135         rp = r->d;
 136
 137         carry = bn_add_words(rp, ap, bp, min);
 138         rp += min;
 139         ap += min;
 140         bp += min;
 141
 142         if (carry) {
 143                 while (dif) {
 144                         dif--;
 145                         t1 = *(ap++);
 146                         t2 = (t1 + 1) & BN_MASK2;
 147                         *(rp++) = t2;
 148                         if (t2) {
 149                                 carry = 0;
 150                                 break;
 151                         }
 152                 }
 153                 if (carry) {
 154                         /* carry != 0 => dif == 0 */
 155                         *rp = 1;
 156                         r->top++;
 157                 }
 158         }
 159         if (dif && rp != ap)
 160                 while (dif--)
 161                         /* copy remaining words if ap != rp */
 162                         *(rp++) = *(ap++);
 163         r->neg = 0;
 164         bn_check_top(r);
 165         return 1;
 166 }
 167
 168 /* unsigned subtraction of b from a, a must be larger than b. */
 169 int
 170 BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
 171 {
 172         int max, min, dif;
 173         BN_ULONG t1, t2, *ap, *bp, *rp;
 174         int i, carry;
 175
 176         bn_check_top(a);
 177         bn_check_top(b);
 178
 179         max = a->top;
 180         min = b->top;
 181         dif = max - min;
 182
 183         if (dif < 0)    /* hmm... should not be happening */
 184         {
 185                 BNerror(BN_R_ARG2_LT_ARG3);
 186                 return (0);
 187         }
 188
 189         if (bn_wexpand(r, max) == NULL)
 190                 return (0);
 191
 192         ap = a->d;
 193         bp = b->d;
 194         rp = r->d;
 195
 196 #if 1
 197         carry = 0;
 198         for (i = min; i != 0; i--) {
 199                 t1= *(ap++);
 200                 t2= *(bp++);
 201                 if (carry) {
 202                         carry = (t1 <= t2);
 203                         t1 = (t1 - t2 - 1)&BN_MASK2;
 204                 } else {
 205                         carry = (t1 < t2);
 206                         t1 = (t1 - t2)&BN_MASK2;
 207                 }
 208                 *(rp++) = t1&BN_MASK2;
 209         }
 210 #else
 211         carry = bn_sub_words(rp, ap, bp, min);
 212         ap += min;
 213         bp += min;
 214         rp += min;
 215 #endif
 216         if (carry) /* subtracted */
 217         {
 218                 if (!dif)
 219                         /* error: a < b */
 220                         return 0;
 221                 while (dif) {
 222                         dif--;
 223                         t1 = *(ap++);
 224                         t2 = (t1 - 1)&BN_MASK2;
 225                         *(rp++) = t2;
 226                         if (t1)
 227                                 break;
 228                 }
 229         }
 230 #if 0
 231         memcpy(rp, ap, sizeof(*rp)*(max - i));
 232 #else
 233         if (rp != ap) {
 234                 for (;;) {
 235                         if (!dif--)
 236                                 break;
 237                         rp[0] = ap[0];
 238                         if (!dif--)
 239                                 break;
 240                         rp[1] = ap[1];
 241                         if (!dif--)
 242                                 break;
 243                         rp[2] = ap[2];
 244                         if (!dif--)
 245                                 break;
 246                         rp[3] = ap[3];
 247                         rp += 4;
 248                         ap += 4;
 249                 }
 250         }
 251 #endif
 252
 253         r->top = max;
 254         r->neg = 0;
 255         bn_correct_top(r);
 256         return (1);
 257 }
 258
 259 int
 260 BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
 261 {
 262         int max;
 263         int add = 0, neg = 0;
 264         const BIGNUM *tmp;
 265
 266         bn_check_top(a);
 267         bn_check_top(b);
 268
 269         /*  a -  b      a-b
 270          *  a - -b      a+b
 271          * -a -  b      -(a+b)
 272          * -a - -b      b-a
 273          */
 274         if (a->neg) {
 275                 if (b->neg) {
 276                         tmp = a;
 277                         a = b;
 278                         b = tmp;
 279                 } else {
 280                         add = 1;
 281                         neg = 1;
 282                 }
 283         } else {
 284                 if (b->neg) {
 285                         add = 1;
 286                         neg = 0;
 287                 }
 288         }
 289
 290         if (add) {
 291                 if (!BN_uadd(r, a, b))
 292                         return (0);
 293                 r->neg = neg;
 294                 return (1);
 295         }
 296
 297         /* We are actually doing a - b :-) */
 298
 299         max = (a->top > b->top) ? a->top : b->top;
 300         if (bn_wexpand(r, max) == NULL)
 301                 return (0);
 302         if (BN_ucmp(a, b) < 0) {
 303                 if (!BN_usub(r, b, a))
 304                         return (0);
 305                 r->neg = 1;
 306         } else {
 307                 if (!BN_usub(r, a, b))
 308                         return (0);
 309                 r->neg = 0;
 310         }
 311         bn_check_top(r);
 312         return (1);
 313 }