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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}
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