bn_add.c revision 1.8
1/* $OpenBSD: bn_add.c,v 1.8 2014/06/12 15:49:28 deraadt 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#include "cryptlib.h" 61#include "bn_lcl.h" 62 63/* r can == a or b */ 64int 65BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 66{ 67 const BIGNUM *tmp; 68 int a_neg = a->neg, ret; 69 70 bn_check_top(a); 71 bn_check_top(b); 72 73 /* a + b a+b 74 * a + -b a-b 75 * -a + b b-a 76 * -a + -b -(a+b) 77 */ 78 if (a_neg ^ b->neg) { 79 /* only one is negative */ 80 if (a_neg) 81 { tmp = a; 82 a = b; 83 b = tmp; 84 } 85 86 /* we are now a - b */ 87 88 if (BN_ucmp(a, b) < 0) { 89 if (!BN_usub(r, b, a)) 90 return (0); 91 r->neg = 1; 92 } else { 93 if (!BN_usub(r, a, b)) 94 return (0); 95 r->neg = 0; 96 } 97 return (1); 98 } 99 100 ret = BN_uadd(r, a, b); 101 r->neg = a_neg; 102 bn_check_top(r); 103 return ret; 104} 105 106/* unsigned add of b to a */ 107int 108BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 109{ 110 int max, min, dif; 111 BN_ULONG *ap, *bp, *rp, carry, t1, t2; 112 const BIGNUM *tmp; 113 114 bn_check_top(a); 115 bn_check_top(b); 116 117 if (a->top < b->top) { 118 tmp = a; 119 a = b; 120 b = tmp; 121 } 122 max = a->top; 123 min = b->top; 124 dif = max - min; 125 126 if (bn_wexpand(r, max + 1) == NULL) 127 return 0; 128 129 r->top = max; 130 131 ap = a->d; 132 bp = b->d; 133 rp = r->d; 134 135 carry = bn_add_words(rp, ap, bp, min); 136 rp += min; 137 ap += min; 138 bp += min; 139 140 if (carry) { 141 while (dif) { 142 dif--; 143 t1 = *(ap++); 144 t2 = (t1 + 1) & BN_MASK2; 145 *(rp++) = t2; 146 if (t2) { 147 carry = 0; 148 break; 149 } 150 } 151 if (carry) { 152 /* carry != 0 => dif == 0 */ 153 *rp = 1; 154 r->top++; 155 } 156 } 157 if (dif && rp != ap) 158 while (dif--) 159 /* copy remaining words if ap != rp */ 160 *(rp++) = *(ap++); 161 r->neg = 0; 162 bn_check_top(r); 163 return 1; 164} 165 166/* unsigned subtraction of b from a, a must be larger than b. */ 167int 168BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 169{ 170 int max, min, dif; 171 register BN_ULONG t1, t2, *ap, *bp, *rp; 172 int i, carry; 173 174 bn_check_top(a); 175 bn_check_top(b); 176 177 max = a->top; 178 min = b->top; 179 dif = max - min; 180 181 if (dif < 0) /* hmm... should not be happening */ 182 { 183 BNerr(BN_F_BN_USUB, BN_R_ARG2_LT_ARG3); 184 return (0); 185 } 186 187 if (bn_wexpand(r, max) == NULL) 188 return (0); 189 190 ap = a->d; 191 bp = b->d; 192 rp = r->d; 193 194#if 1 195 carry = 0; 196 for (i = min; i != 0; i--) { 197 t1= *(ap++); 198 t2= *(bp++); 199 if (carry) { 200 carry = (t1 <= t2); 201 t1 = (t1 - t2 - 1)&BN_MASK2; 202 } else { 203 carry = (t1 < t2); 204 t1 = (t1 - t2)&BN_MASK2; 205 } 206 *(rp++) = t1&BN_MASK2; 207 } 208#else 209 carry = bn_sub_words(rp, ap, bp, min); 210 ap += min; 211 bp += min; 212 rp += min; 213#endif 214 if (carry) /* subtracted */ 215 { 216 if (!dif) 217 /* error: a < b */ 218 return 0; 219 while (dif) { 220 dif--; 221 t1 = *(ap++); 222 t2 = (t1 - 1)&BN_MASK2; 223 *(rp++) = t2; 224 if (t1) 225 break; 226 } 227 } 228#if 0 229 memcpy(rp, ap, sizeof(*rp)*(max - i)); 230#else 231 if (rp != ap) { 232 for (;;) { 233 if (!dif--) 234 break; 235 rp[0] = ap[0]; 236 if (!dif--) 237 break; 238 rp[1] = ap[1]; 239 if (!dif--) 240 break; 241 rp[2] = ap[2]; 242 if (!dif--) 243 break; 244 rp[3] = ap[3]; 245 rp += 4; 246 ap += 4; 247 } 248 } 249#endif 250 251 r->top = max; 252 r->neg = 0; 253 bn_correct_top(r); 254 return (1); 255} 256 257int 258BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 259{ 260 int max; 261 int add = 0, neg = 0; 262 const BIGNUM *tmp; 263 264 bn_check_top(a); 265 bn_check_top(b); 266 267 /* a - b a-b 268 * a - -b a+b 269 * -a - b -(a+b) 270 * -a - -b b-a 271 */ 272 if (a->neg) { 273 if (b->neg) { 274 tmp = a; 275 a = b; 276 b = tmp; 277 } else { 278 add = 1; 279 neg = 1; 280 } 281 } else { 282 if (b->neg) { 283 add = 1; 284 neg = 0; 285 } 286 } 287 288 if (add) { 289 if (!BN_uadd(r, a, b)) 290 return (0); 291 r->neg = neg; 292 return (1); 293 } 294 295 /* We are actually doing a - b :-) */ 296 297 max = (a->top > b->top) ? a->top : b->top; 298 if (bn_wexpand(r, max) == NULL) 299 return (0); 300 if (BN_ucmp(a, b) < 0) { 301 if (!BN_usub(r, b, a)) 302 return (0); 303 r->neg = 1; 304 } else { 305 if (!BN_usub(r, a, b)) 306 return (0); 307 r->neg = 0; 308 } 309 bn_check_top(r); 310 return (1); 311} 312