bn_add.c revision 1.16 
1/* $OpenBSD: bn_add.c,v 1.16 2022/11/26 16:08:51 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_local.h"
64
65int
66BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
67{
68	int ret, r_neg;
69
70
71	if (a->neg == b->neg) {
72		r_neg = a->neg;
73		ret = BN_uadd(r, a, b);
74	} else {
75		int cmp = BN_ucmp(a, b);
76
77		if (cmp > 0) {
78			r_neg = a->neg;
79			ret = BN_usub(r, a, b);
80		} else if (cmp < 0) {
81			r_neg = b->neg;
82			ret = BN_usub(r, b, a);
83		} else {
84			r_neg = 0;
85			BN_zero(r);
86			ret = 1;
87		}
88	}
89
90	r->neg = r_neg;
91	return ret;
92}
93
94int
95BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
96{
97	int max, min, dif;
98	const BN_ULONG *ap, *bp;
99	BN_ULONG *rp, carry, t1, t2;
100
101
102	if (a->top < b->top) {
103		const BIGNUM *tmp;
104
105		tmp = a;
106		a = b;
107		b = tmp;
108	}
109	max = a->top;
110	min = b->top;
111	dif = max - min;
112
113	if (!bn_wexpand(r, max + 1))
114		return 0;
115
116	r->top = max;
117
118	ap = a->d;
119	bp = b->d;
120	rp = r->d;
121
122	carry = bn_add_words(rp, ap, bp, min);
123	rp += min;
124	ap += min;
125
126	while (dif) {
127		dif--;
128		t1 = *(ap++);
129		t2 = (t1 + carry) & BN_MASK2;
130		*(rp++) = t2;
131		carry &= (t2 == 0);
132	}
133	*rp = carry;
134	r->top += carry;
135
136	r->neg = 0;
137	return 1;
138}
139
140int
141BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
142{
143	int max, min, dif;
144	const BN_ULONG *ap, *bp;
145	BN_ULONG t1, t2, borrow, *rp;
146
147
148	max = a->top;
149	min = b->top;
150	dif = max - min;
151
152	if (dif < 0) {
153		BNerror(BN_R_ARG2_LT_ARG3);
154		return 0;
155	}
156
157	if (!bn_wexpand(r, max))
158		return 0;
159
160	ap = a->d;
161	bp = b->d;
162	rp = r->d;
163
164	borrow = bn_sub_words(rp, ap, bp, min);
165	ap += min;
166	rp += min;
167
168	while (dif) {
169		dif--;
170		t1 = *(ap++);
171		t2 = (t1 - borrow) & BN_MASK2;
172		*(rp++) = t2;
173		borrow &= (t1 == 0);
174	}
175
176	while (max > 0 && *--rp == 0)
177		max--;
178
179	r->top = max;
180	r->neg = 0;
181	bn_correct_top(r);
182	return 1;
183}
184
185int
186BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
187{
188	int ret, r_neg;
189
190
191	if (a->neg != b->neg) {
192		r_neg = a->neg;
193		ret = BN_uadd(r, a, b);
194	} else {
195		int cmp = BN_ucmp(a, b);
196
197		if (cmp > 0) {
198			r_neg = a->neg;
199			ret = BN_usub(r, a, b);
200		} else if (cmp < 0) {
201			r_neg = !b->neg;
202			ret = BN_usub(r, b, a);
203		} else {
204			r_neg = 0;
205			BN_zero(r);
206			ret = 1;
207		}
208	}
209
210	r->neg = r_neg;
211	return ret;
212}
213