1/*
2 * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License").  You may not use
5 * this file except in compliance with the License.  You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10#include "internal/cryptlib.h"
11#include "bn_local.h"
12
13/* signed add of b to a. */
14int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
15{
16    int ret, r_neg, cmp_res;
17
18    bn_check_top(a);
19    bn_check_top(b);
20
21    if (a->neg == b->neg) {
22        r_neg = a->neg;
23        ret = BN_uadd(r, a, b);
24    } else {
25        cmp_res = BN_ucmp(a, b);
26        if (cmp_res > 0) {
27            r_neg = a->neg;
28            ret = BN_usub(r, a, b);
29        } else if (cmp_res < 0) {
30            r_neg = b->neg;
31            ret = BN_usub(r, b, a);
32        } else {
33            r_neg = 0;
34            BN_zero(r);
35            ret = 1;
36        }
37    }
38
39    r->neg = r_neg;
40    bn_check_top(r);
41    return ret;
42}
43
44/* signed sub of b from a. */
45int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
46{
47    int ret, r_neg, cmp_res;
48
49    bn_check_top(a);
50    bn_check_top(b);
51
52    if (a->neg != b->neg) {
53        r_neg = a->neg;
54        ret = BN_uadd(r, a, b);
55    } else {
56        cmp_res = BN_ucmp(a, b);
57        if (cmp_res > 0) {
58            r_neg = a->neg;
59            ret = BN_usub(r, a, b);
60        } else if (cmp_res < 0) {
61            r_neg = !b->neg;
62            ret = BN_usub(r, b, a);
63        } else {
64            r_neg = 0;
65            BN_zero(r);
66            ret = 1;
67        }
68    }
69
70    r->neg = r_neg;
71    bn_check_top(r);
72    return ret;
73}
74
75/* unsigned add of b to a, r can be equal to a or b. */
76int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
77{
78    int max, min, dif;
79    const BN_ULONG *ap, *bp;
80    BN_ULONG *rp, carry, t1, t2;
81
82    bn_check_top(a);
83    bn_check_top(b);
84
85    if (a->top < b->top) {
86        const BIGNUM *tmp;
87
88        tmp = a;
89        a = b;
90        b = tmp;
91    }
92    max = a->top;
93    min = b->top;
94    dif = max - min;
95
96    if (bn_wexpand(r, max + 1) == NULL)
97        return 0;
98
99    r->top = max;
100
101    ap = a->d;
102    bp = b->d;
103    rp = r->d;
104
105    carry = bn_add_words(rp, ap, bp, min);
106    rp += min;
107    ap += min;
108
109    while (dif) {
110        dif--;
111        t1 = *(ap++);
112        t2 = (t1 + carry) & BN_MASK2;
113        *(rp++) = t2;
114        carry &= (t2 == 0);
115    }
116    *rp = carry;
117    r->top += carry;
118
119    r->neg = 0;
120    bn_check_top(r);
121    return 1;
122}
123
124/* unsigned subtraction of b from a, a must be larger than b. */
125int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
126{
127    int max, min, dif;
128    BN_ULONG t1, t2, borrow, *rp;
129    const BN_ULONG *ap, *bp;
130
131    bn_check_top(a);
132    bn_check_top(b);
133
134    max = a->top;
135    min = b->top;
136    dif = max - min;
137
138    if (dif < 0) {              /* hmm... should not be happening */
139        ERR_raise(ERR_LIB_BN, BN_R_ARG2_LT_ARG3);
140        return 0;
141    }
142
143    if (bn_wexpand(r, max) == NULL)
144        return 0;
145
146    ap = a->d;
147    bp = b->d;
148    rp = r->d;
149
150    borrow = bn_sub_words(rp, ap, bp, min);
151    ap += min;
152    rp += min;
153
154    while (dif) {
155        dif--;
156        t1 = *(ap++);
157        t2 = (t1 - borrow) & BN_MASK2;
158        *(rp++) = t2;
159        borrow &= (t1 == 0);
160    }
161
162    while (max && *--rp == 0)
163        max--;
164
165    r->top = max;
166    r->neg = 0;
167    bn_pollute(r);
168
169    return 1;
170}
171
172