bn_add.c revision 296465 
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, ret;
68
69    bn_check_top(a);
70    bn_check_top(b);
71
72    /*-
73     *  a +  b      a+b
74     *  a + -b      a-b
75     * -a +  b      b-a
76     * -a + -b      -(a+b)
77     */
78    if (a_neg ^ b->neg) {
79        /* only one is negative */
80        if (a_neg) {
81            tmp = a;
82            a = b;
83            b = tmp;
84        }
85
86        /* we are now a - b */
87
88        if (BN_ucmp(a, b) < 0) {
89            if (!BN_usub(r, b, a))
90                return (0);
91            r->neg = 1;
92        } else {
93            if (!BN_usub(r, a, b))
94                return (0);
95            r->neg = 0;
96        }
97        return (1);
98    }
99
100    ret = BN_uadd(r, a, b);
101    r->neg = a_neg;
102    bn_check_top(r);
103    return ret;
104}
105
106/* unsigned add of b to a */
107int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
108{
109    int max, min, dif;
110    BN_ULONG *ap, *bp, *rp, carry, t1, t2;
111    const BIGNUM *tmp;
112
113    bn_check_top(a);
114    bn_check_top(b);
115
116    if (a->top < b->top) {
117        tmp = a;
118        a = b;
119        b = tmp;
120    }
121    max = a->top;
122    min = b->top;
123    dif = max - min;
124
125    if (bn_wexpand(r, max + 1) == NULL)
126        return 0;
127
128    r->top = max;
129
130    ap = a->d;
131    bp = b->d;
132    rp = r->d;
133
134    carry = bn_add_words(rp, ap, bp, min);
135    rp += min;
136    ap += min;
137    bp += min;
138
139    if (carry) {
140        while (dif) {
141            dif--;
142            t1 = *(ap++);
143            t2 = (t1 + 1) & BN_MASK2;
144            *(rp++) = t2;
145            if (t2) {
146                carry = 0;
147                break;
148            }
149        }
150        if (carry) {
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. */
166int 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        BNerr(BN_F_BN_USUB, BN_R_ARG2_LT_ARG3);
184        return (0);
185    }
186
187    if (bn_wexpand(r, max) == NULL)
188        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        t1 = *(ap++);
198        t2 = *(bp++);
199        if (carry) {
200            carry = (t1 <= t2);
201            t1 = (t1 - t2 - 1) & BN_MASK2;
202        } else {
203            carry = (t1 < t2);
204            t1 = (t1 - t2) & BN_MASK2;
205        }
206# if defined(IRIX_CC_BUG) && !defined(LINT)
207        dummy = t1;
208# endif
209        *(rp++) = t1 & BN_MASK2;
210    }
211#else
212    carry = bn_sub_words(rp, ap, bp, min);
213    ap += min;
214    bp += min;
215    rp += min;
216#endif
217    if (carry) {                /* subtracted */
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 BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
260{
261    int max;
262    int add = 0, neg = 0;
263    const BIGNUM *tmp;
264
265    bn_check_top(a);
266    bn_check_top(b);
267
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}
314