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 */
64 int 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 /* 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 ret = BN_uadd(r,a,b);
99 r->neg = a_neg;
100 bn_check_top(r);
101 return ret;
102 }
103
104 /* unsigned add of b to a */
105 int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
106 {
107 int max,min,dif;
108 BN_ULONG *ap,*bp,*rp,carry,t1,t2;
109 const BIGNUM *tmp;
110
111 bn_check_top(a);
112 bn_check_top(b);
113
114 if (a->top < b->top)
115 { tmp=a; a=b; b=tmp; }
116 max = a->top;
117 min = b->top;
118 dif = max - min;
119
120 if (bn_wexpand(r,max+1) == NULL)
121 return 0;
122
123 r->top=max;
124
125
126 ap=a->d;
127 bp=b->d;
128 rp=r->d;
129
130 carry=bn_add_words(rp,ap,bp,min);
131 rp+=min;
132 ap+=min;
133 bp+=min;
134
135 if (carry)
136 {
137 while (dif)
138 {
139 dif--;
140 t1 = *(ap++);
141 t2 = (t1+1) & BN_MASK2;
142 *(rp++) = t2;
143 if (t2)
144 {
145 carry=0;
146 break;
147 }
148 }
149 if (carry)
150 {
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. */
166 int 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 {
184 BNerr(BN_F_BN_USUB,BN_R_ARG2_LT_ARG3);
185 return(0);
186 }
187
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 = min; i != 0; 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 #endif
221 if (carry) /* subtracted */
222 {
223 if (!dif)
224 /* error: a < b */
225 return 0;
226 while (dif)
227 {
228 dif--;
229 t1 = *(ap++);
230 t2 = (t1-1)&BN_MASK2;
231 *(rp++) = t2;
232 if (t1)
233 break;
234 }
235 }
236 #if 0
237 memcpy(rp,ap,sizeof(*rp)*(max-i));
238 #else
239 if (rp != ap)
240 {
241 for (;;)
242 {
243 if (!dif--) break;
244 rp[0]=ap[0];
245 if (!dif--) break;
246 rp[1]=ap[1];
247 if (!dif--) break;
248 rp[2]=ap[2];
249 if (!dif--) break;
250 rp[3]=ap[3];
251 rp+=4;
252 ap+=4;
253 }
254 }
255 #endif
256
257 r->top=max;
258 r->neg=0;
259 bn_correct_top(r);
260 return(1);
261 }
262
263 int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
264 {
265 int max;
266 int add=0,neg=0;
267 const BIGNUM *tmp;
268
269 bn_check_top(a);
270 bn_check_top(b);
271
272 /* a - b a-b
273 * a - -b a+b
274 * -a - b -(a+b)
275 * -a - -b b-a
276 */
277 if (a->neg)
278 {
279 if (b->neg)
280 { tmp=a; a=b; b=tmp; }
281 else
282 { add=1; neg=1; }
283 }
284 else
285 {
286 if (b->neg) { add=1; neg=0; }
287 }
288
289 if (add)
290 {
291 if (!BN_uadd(r,a,b)) return(0);
292 r->neg=neg;
293 return(1);
294 }
295
296 /* We are actually doing a - b :-) */
297
298 max=(a->top > b->top)?a->top:b->top;
299 if (bn_wexpand(r,max) == NULL) return(0);
300 if (BN_ucmp(a,b) < 0)
301 {
302 if (!BN_usub(r,b,a)) return(0);
303 r->neg=1;
304 }
305 else
306 {
307 if (!BN_usub(r,a,b)) return(0);
308 r->neg=0;
309 }
310 bn_check_top(r);
311 return(1);
312 }