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. */
BN_add(BIGNUM * r,const BIGNUM * a,const BIGNUM * b)14 int 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. */
BN_sub(BIGNUM * r,const BIGNUM * a,const BIGNUM * b)45 int 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. */
BN_uadd(BIGNUM * r,const BIGNUM * a,const BIGNUM * b)76 int 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. */
BN_usub(BIGNUM * r,const BIGNUM * a,const BIGNUM * b)125 int 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