bn_add.c revision 1.4
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; 68 69 bn_check_top(a); 70 bn_check_top(b); 71 72 /* a + b a+b 73 * a + -b a-b 74 * -a + b b-a 75 * -a + -b -(a+b) 76 */ 77 if (a_neg ^ b->neg) 78 { 79 /* only one is negative */ 80 if (a_neg) 81 { tmp=a; a=b; b=tmp; } 82 83 /* we are now a - b */ 84 85 if (BN_ucmp(a,b) < 0) 86 { 87 if (!BN_usub(r,b,a)) return(0); 88 r->neg=1; 89 } 90 else 91 { 92 if (!BN_usub(r,a,b)) return(0); 93 r->neg=0; 94 } 95 return(1); 96 } 97 98 if (!BN_uadd(r,a,b)) return(0); 99 if (a_neg) /* both are neg */ 100 r->neg=1; 101 else 102 r->neg=0; 103 return(1); 104 } 105 106/* unsigned add of b to a, r must be large enough */ 107int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 108 { 109 register int i; 110 int max,min; 111 BN_ULONG *ap,*bp,*rp,carry,t1; 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; a=b; b=tmp; } 119 max=a->top; 120 min=b->top; 121 122 if (bn_wexpand(r,max+1) == NULL) 123 return(0); 124 125 r->top=max; 126 127 128 ap=a->d; 129 bp=b->d; 130 rp=r->d; 131 carry=0; 132 133 carry=bn_add_words(rp,ap,bp,min); 134 rp+=min; 135 ap+=min; 136 bp+=min; 137 i=min; 138 139 if (carry) 140 { 141 while (i < max) 142 { 143 i++; 144 t1= *(ap++); 145 if ((*(rp++)=(t1+1)&BN_MASK2) >= t1) 146 { 147 carry=0; 148 break; 149 } 150 } 151 if ((i >= max) && carry) 152 { 153 *(rp++)=1; 154 r->top++; 155 } 156 } 157 if (rp != ap) 158 { 159 for (; i<max; i++) 160 *(rp++)= *(ap++); 161 } 162 /* memcpy(rp,ap,sizeof(*ap)*(max-i));*/ 163 r->neg = 0; 164 return(1); 165 } 166 167/* unsigned subtraction of b from a, a must be larger than b. */ 168int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) 169 { 170 int max,min; 171 register BN_ULONG t1,t2,*ap,*bp,*rp; 172 int i,carry; 173#if defined(IRIX_CC_BUG) && !defined(LINT) 174 int dummy; 175#endif 176 177 bn_check_top(a); 178 bn_check_top(b); 179 180 if (a->top < b->top) /* hmm... should not be happening */ 181 { 182 BNerr(BN_F_BN_USUB,BN_R_ARG2_LT_ARG3); 183 return(0); 184 } 185 186 max=a->top; 187 min=b->top; 188 if (bn_wexpand(r,max) == NULL) 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=0; i<min; i++) 197 { 198 t1= *(ap++); 199 t2= *(bp++); 200 if (carry) 201 { 202 carry=(t1 <= t2); 203 t1=(t1-t2-1)&BN_MASK2; 204 } 205 else 206 { 207 carry=(t1 < t2); 208 t1=(t1-t2)&BN_MASK2; 209 } 210#if defined(IRIX_CC_BUG) && !defined(LINT) 211 dummy=t1; 212#endif 213 *(rp++)=t1&BN_MASK2; 214 } 215#else 216 carry=bn_sub_words(rp,ap,bp,min); 217 ap+=min; 218 bp+=min; 219 rp+=min; 220 i=min; 221#endif 222 if (carry) /* subtracted */ 223 { 224 while (i < max) 225 { 226 i++; 227 t1= *(ap++); 228 t2=(t1-1)&BN_MASK2; 229 *(rp++)=t2; 230 if (t1 > t2) break; 231 } 232 } 233#if 0 234 memcpy(rp,ap,sizeof(*rp)*(max-i)); 235#else 236 if (rp != ap) 237 { 238 for (;;) 239 { 240 if (i++ >= max) break; 241 rp[0]=ap[0]; 242 if (i++ >= max) break; 243 rp[1]=ap[1]; 244 if (i++ >= max) break; 245 rp[2]=ap[2]; 246 if (i++ >= max) break; 247 rp[3]=ap[3]; 248 rp+=4; 249 ap+=4; 250 } 251 } 252#endif 253 254 r->top=max; 255 r->neg=0; 256 bn_fix_top(r); 257 return(1); 258 } 259 260int 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 { 276 if (b->neg) 277 { tmp=a; a=b; b=tmp; } 278 else 279 { add=1; neg=1; } 280 } 281 else 282 { 283 if (b->neg) { add=1; neg=0; } 284 } 285 286 if (add) 287 { 288 if (!BN_uadd(r,a,b)) return(0); 289 r->neg=neg; 290 return(1); 291 } 292 293 /* We are actually doing a - b :-) */ 294 295 max=(a->top > b->top)?a->top:b->top; 296 if (bn_wexpand(r,max) == NULL) return(0); 297 if (BN_ucmp(a,b) < 0) 298 { 299 if (!BN_usub(r,b,a)) return(0); 300 r->neg=1; 301 } 302 else 303 { 304 if (!BN_usub(r,a,b)) return(0); 305 r->neg=0; 306 } 307 return(1); 308 } 309 310