1/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
2 * All rights reserved.
3 *
4 * This package is an SSL implementation written
5 * by Eric Young (eay@cryptsoft.com).
6 * The implementation was written so as to conform with Netscapes SSL.
7 *
8 * This library is free for commercial and non-commercial use as long as
9 * the following conditions are aheared to.  The following conditions
10 * apply to all code found in this distribution, be it the RC4, RSA,
11 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
12 * included with this distribution is covered by the same copyright terms
13 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
14 *
15 * Copyright remains Eric Young's, and as such any Copyright notices in
16 * the code are not to be removed.
17 * If this package is used in a product, Eric Young should be given attribution
18 * as the author of the parts of the library used.
19 * This can be in the form of a textual message at program startup or
20 * in documentation (online or textual) provided with the package.
21 *
22 * Redistribution and use in source and binary forms, with or without
23 * modification, are permitted provided that the following conditions
24 * are met:
25 * 1. Redistributions of source code must retain the copyright
26 *    notice, this list of conditions and the following disclaimer.
27 * 2. Redistributions in binary form must reproduce the above copyright
28 *    notice, this list of conditions and the following disclaimer in the
29 *    documentation and/or other materials provided with the distribution.
30 * 3. All advertising materials mentioning features or use of this software
31 *    must display the following acknowledgement:
32 *    "This product includes cryptographic software written by
33 *     Eric Young (eay@cryptsoft.com)"
34 *    The word 'cryptographic' can be left out if the rouines from the library
35 *    being used are not cryptographic related :-).
36 * 4. If you include any Windows specific code (or a derivative thereof) from
37 *    the apps directory (application code) you must include an acknowledgement:
38 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
39 *
40 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
41 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
42 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
43 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
44 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
45 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
46 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
47 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
48 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
49 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
50 * SUCH DAMAGE.
51 *
52 * The licence and distribution terms for any publically available version or
53 * derivative of this code cannot be changed.  i.e. this code cannot simply be
54 * copied and put under another distribution licence
55 * [including the GNU Public Licence.] */
56
57#include <openssl/bn.h>
58
59#include <string.h>
60
61#include <openssl/err.h>
62#include <openssl/mem.h>
63
64#include "internal.h"
65
66
67int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) {
68  const BIGNUM *tmp;
69  int a_neg = a->neg, ret;
70
71  //  a +  b	a+b
72  //  a + -b	a-b
73  // -a +  b	b-a
74  // -a + -b	-(a+b)
75  if (a_neg ^ b->neg) {
76    // only one is negative
77    if (a_neg) {
78      tmp = a;
79      a = b;
80      b = tmp;
81    }
82
83    // we are now a - b
84    if (BN_ucmp(a, b) < 0) {
85      if (!BN_usub(r, b, a)) {
86        return 0;
87      }
88      r->neg = 1;
89    } else {
90      if (!BN_usub(r, a, b)) {
91        return 0;
92      }
93      r->neg = 0;
94    }
95    return 1;
96  }
97
98  ret = BN_uadd(r, a, b);
99  r->neg = a_neg;
100  return ret;
101}
102
103int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) {
104  int max, min, dif;
105  BN_ULONG *ap, *bp, *rp, carry, t1, t2;
106  const BIGNUM *tmp;
107
108  if (a->top < b->top) {
109    tmp = a;
110    a = b;
111    b = tmp;
112  }
113  max = a->top;
114  min = b->top;
115  dif = max - min;
116
117  if (!bn_wexpand(r, max + 1)) {
118    return 0;
119  }
120
121  r->top = max;
122
123  ap = a->d;
124  bp = b->d;
125  rp = r->d;
126
127  carry = bn_add_words(rp, ap, bp, min);
128  rp += min;
129  ap += min;
130  bp += min;
131
132  if (carry) {
133    while (dif) {
134      dif--;
135      t1 = *(ap++);
136      t2 = t1 + 1;
137      *(rp++) = t2;
138      if (t2) {
139        carry = 0;
140        break;
141      }
142    }
143    if (carry) {
144      // carry != 0 => dif == 0
145      *rp = 1;
146      r->top++;
147    }
148  }
149
150  if (dif && rp != ap) {
151    while (dif--) {
152      // copy remaining words if ap != rp
153      *(rp++) = *(ap++);
154    }
155  }
156
157  r->neg = 0;
158  return 1;
159}
160
161int BN_add_word(BIGNUM *a, BN_ULONG w) {
162  BN_ULONG l;
163  int i;
164
165  // degenerate case: w is zero
166  if (!w) {
167    return 1;
168  }
169
170  // degenerate case: a is zero
171  if (BN_is_zero(a)) {
172    return BN_set_word(a, w);
173  }
174
175  // handle 'a' when negative
176  if (a->neg) {
177    a->neg = 0;
178    i = BN_sub_word(a, w);
179    if (!BN_is_zero(a)) {
180      a->neg = !(a->neg);
181    }
182    return i;
183  }
184
185  for (i = 0; w != 0 && i < a->top; i++) {
186    a->d[i] = l = a->d[i] + w;
187    w = (w > l) ? 1 : 0;
188  }
189
190  if (w && i == a->top) {
191    if (!bn_wexpand(a, a->top + 1)) {
192      return 0;
193    }
194    a->top++;
195    a->d[i] = w;
196  }
197
198  return 1;
199}
200
201int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) {
202  int add = 0, neg = 0;
203  const BIGNUM *tmp;
204
205  //  a -  b	a-b
206  //  a - -b	a+b
207  // -a -  b	-(a+b)
208  // -a - -b	b-a
209  if (a->neg) {
210    if (b->neg) {
211      tmp = a;
212      a = b;
213      b = tmp;
214    } else {
215      add = 1;
216      neg = 1;
217    }
218  } else {
219    if (b->neg) {
220      add = 1;
221      neg = 0;
222    }
223  }
224
225  if (add) {
226    if (!BN_uadd(r, a, b)) {
227      return 0;
228    }
229
230    r->neg = neg;
231    return 1;
232  }
233
234  if (BN_ucmp(a, b) < 0) {
235    if (!BN_usub(r, b, a)) {
236      return 0;
237    }
238    r->neg = 1;
239  } else {
240    if (!BN_usub(r, a, b)) {
241      return 0;
242    }
243    r->neg = 0;
244  }
245
246  return 1;
247}
248
249int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) {
250  int max, min, dif;
251  register BN_ULONG t1, t2, *ap, *bp, *rp;
252  int i, carry;
253
254  max = a->top;
255  min = b->top;
256  dif = max - min;
257
258  if (dif < 0)  // hmm... should not be happening
259  {
260    OPENSSL_PUT_ERROR(BN, BN_R_ARG2_LT_ARG3);
261    return 0;
262  }
263
264  if (!bn_wexpand(r, max)) {
265    return 0;
266  }
267
268  ap = a->d;
269  bp = b->d;
270  rp = r->d;
271
272  carry = 0;
273  for (i = min; i != 0; i--) {
274    t1 = *(ap++);
275    t2 = *(bp++);
276    if (carry) {
277      carry = (t1 <= t2);
278      t1 -= t2 + 1;
279    } else {
280      carry = (t1 < t2);
281      t1 -= t2;
282    }
283    *(rp++) = t1;
284  }
285
286  if (carry)  // subtracted
287  {
288    if (!dif) {
289      // error: a < b
290      return 0;
291    }
292
293    while (dif) {
294      dif--;
295      t1 = *(ap++);
296      t2 = t1 - 1;
297      *(rp++) = t2;
298      if (t1) {
299        break;
300      }
301    }
302  }
303
304  if (dif > 0 && rp != ap) {
305    OPENSSL_memcpy(rp, ap, sizeof(*rp) * dif);
306  }
307
308  r->top = max;
309  r->neg = 0;
310  bn_correct_top(r);
311
312  return 1;
313}
314
315int BN_sub_word(BIGNUM *a, BN_ULONG w) {
316  int i;
317
318  // degenerate case: w is zero
319  if (!w) {
320    return 1;
321  }
322
323  // degenerate case: a is zero
324  if (BN_is_zero(a)) {
325    i = BN_set_word(a, w);
326    if (i != 0) {
327      BN_set_negative(a, 1);
328    }
329    return i;
330  }
331
332  // handle 'a' when negative
333  if (a->neg) {
334    a->neg = 0;
335    i = BN_add_word(a, w);
336    a->neg = 1;
337    return i;
338  }
339
340  if ((a->top == 1) && (a->d[0] < w)) {
341    a->d[0] = w - a->d[0];
342    a->neg = 1;
343    return 1;
344  }
345
346  i = 0;
347  for (;;) {
348    if (a->d[i] >= w) {
349      a->d[i] -= w;
350      break;
351    } else {
352      a->d[i] -= w;
353      i++;
354      w = 1;
355    }
356  }
357
358  if ((a->d[i] == 0) && (i == (a->top - 1))) {
359    a->top--;
360  }
361
362  return 1;
363}
364