bn_add.c revision 1.13 
1/* $OpenBSD: bn_add.c,v 1.13 2018/07/23 18:07:21 tb 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
65int
66BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
67{
68	int ret, r_neg;
69
70	bn_check_top(a);
71	bn_check_top(b);
72
73	if (a->neg == b->neg) {
74		r_neg = a->neg;
75		ret = BN_uadd(r, a, b);
76	} else {
77		int cmp = BN_ucmp(a, b);
78
79		if (cmp > 0) {
80			r_neg = a->neg;
81			ret = BN_usub(r, a, b);
82		} else if (cmp < 0) {
83			r_neg = b->neg;
84			ret = BN_usub(r, b, a);
85		} else {
86			r_neg = 0;
87			BN_zero(r);
88			ret = 1;
89		}
90	}
91
92	r->neg = r_neg;
93	bn_check_top(r);
94	return ret;
95}
96
97int
98BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
99{
100	int max, min, dif;
101	const BN_ULONG *ap, *bp;
102	BN_ULONG *rp, carry, t1, t2;
103
104	bn_check_top(a);
105	bn_check_top(b);
106
107	if (a->top < b->top) {
108		const BIGNUM *tmp;
109
110		tmp = a;
111		a = b;
112		b = tmp;
113	}
114	max = a->top;
115	min = b->top;
116	dif = max - min;
117
118	if (bn_wexpand(r, max + 1) == NULL)
119		return 0;
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
131	while (dif) {
132		dif--;
133		t1 = *(ap++);
134		t2 = (t1 + carry) & BN_MASK2;
135		*(rp++) = t2;
136		carry &= (t2 == 0);
137	}
138	*rp = carry;
139	r->top += carry;
140
141	r->neg = 0;
142	bn_check_top(r);
143	return 1;
144}
145
146int
147BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
148{
149	int max, min, dif;
150	const BN_ULONG *ap, *bp;
151	BN_ULONG t1, t2, borrow, *rp;
152
153	bn_check_top(a);
154	bn_check_top(b);
155
156	max = a->top;
157	min = b->top;
158	dif = max - min;
159
160	if (dif < 0) {
161		BNerror(BN_R_ARG2_LT_ARG3);
162		return 0;
163	}
164
165	if (bn_wexpand(r, max) == NULL)
166		return 0;
167
168	ap = a->d;
169	bp = b->d;
170	rp = r->d;
171
172	borrow = bn_sub_words(rp, ap, bp, min);
173	ap += min;
174	rp += min;
175
176	while (dif) {
177		dif--;
178		t1 = *(ap++);
179		t2 = (t1 - borrow) & BN_MASK2;
180		*(rp++) = t2;
181		borrow &= (t1 == 0);
182	}
183
184	while (max > 0 && *--rp == 0)
185		max--;
186
187	r->top = max;
188	r->neg = 0;
189	bn_correct_top(r);
190	return 1;
191}
192
193int
194BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
195{
196	int ret, r_neg;
197
198	bn_check_top(a);
199	bn_check_top(b);
200
201	if (a->neg != b->neg) {
202		r_neg = a->neg;
203		ret = BN_uadd(r, a, b);
204	} else {
205		int cmp = BN_ucmp(a, b);
206
207		if (cmp > 0) {
208			r_neg = a->neg;
209			ret = BN_usub(r, a, b);
210		} else if (cmp < 0) {
211			r_neg = !b->neg;
212			ret = BN_usub(r, b, a);
213		} else {
214			r_neg = 0;
215			BN_zero(r);
216			ret = 1;
217		}
218	}
219
220	r->neg = r_neg;
221	bn_check_top(r);
222	return ret;
223}
224