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bn_add.c
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1 /* crypto/bn/bn_add.c */
2 /* Copyright (C) 1995-1998 Eric Young ([email protected])
3  * All rights reserved.
4  *
5  * This package is an SSL implementation written
6  * by Eric Young ([email protected]).
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 ([email protected]).
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 ([email protected])"
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 ([email protected])"
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  {
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  }
313