bn_add.c revision 280304
1/* crypto/bn/bn_add.c */ 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 BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 65{ 66 const BIGNUM *tmp; 67 int a_neg = a->neg, ret; 68 69 bn_check_top(a); 70 bn_check_top(b); 71 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 BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 108{ 109 int max, min, dif; 110 BN_ULONG *ap, *bp, *rp, carry, t1, t2; 111 const BIGNUM *tmp; 112 113 bn_check_top(a); 114 bn_check_top(b); 115 116 if (a->top < b->top) { 117 tmp = a; 118 a = b; 119 b = tmp; 120 } 121 max = a->top; 122 min = b->top; 123 dif = max - min; 124 125 if (bn_wexpand(r, max + 1) == NULL) 126 return 0; 127 128 r->top = max; 129 130 ap = a->d; 131 bp = b->d; 132 rp = r->d; 133 134 carry = bn_add_words(rp, ap, bp, min); 135 rp += min; 136 ap += min; 137 bp += min; 138 139 if (carry) { 140 while (dif) { 141 dif--; 142 t1 = *(ap++); 143 t2 = (t1 + 1) & BN_MASK2; 144 *(rp++) = t2; 145 if (t2) { 146 carry = 0; 147 break; 148 } 149 } 150 if (carry) { 151 /* carry != 0 => dif == 0 */ 152 *rp = 1; 153 r->top++; 154 } 155 } 156 if (dif && rp != ap) 157 while (dif--) 158 /* copy remaining words if ap != rp */ 159 *(rp++) = *(ap++); 160 r->neg = 0; 161 bn_check_top(r); 162 return 1; 163} 164 165/* unsigned subtraction of b from a, a must be larger than b. */ 166int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 167{ 168 int max, min, dif; 169 register BN_ULONG t1, t2, *ap, *bp, *rp; 170 int i, carry; 171#if defined(IRIX_CC_BUG) && !defined(LINT) 172 int dummy; 173#endif 174 175 bn_check_top(a); 176 bn_check_top(b); 177 178 max = a->top; 179 min = b->top; 180 dif = max - min; 181 182 if (dif < 0) { /* hmm... should not be happening */ 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# if defined(IRIX_CC_BUG) && !defined(LINT) 207 dummy = t1; 208# endif 209 *(rp++) = t1 & BN_MASK2; 210 } 211#else 212 carry = bn_sub_words(rp, ap, bp, min); 213 ap += min; 214 bp += min; 215 rp += min; 216#endif 217 if (carry) { /* subtracted */ 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 BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 260{ 261 int max; 262 int add = 0, neg = 0; 263 const BIGNUM *tmp; 264 265 bn_check_top(a); 266 bn_check_top(b); 267 268 /*- 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