bn_add.c revision 1.10
1/* $OpenBSD: bn_add.c,v 1.10 2014/10/28 07:35:58 jsg 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 */ 66int 67BN_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 */ 109int 110BN_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. */ 169int 170BN_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 BNerr(BN_F_BN_USUB, 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 259int 260BN_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} 314