1/*
2 * Copyright 1995-2016 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
13BN_ULONG BN_mod_word(const BIGNUM *a, BN_ULONG w)
14{
15#ifndef BN_LLONG
16 BN_ULONG ret = 0;
17#else
18 BN_ULLONG ret = 0;
19#endif
20 int i;
21
22 if (w == 0)
23 return (BN_ULONG)-1;
24
25#ifndef BN_LLONG
26 /*
27 * If |w| is too long and we don't have BN_ULLONG then we need to fall
28 * back to using BN_div_word
29 */
30 if (w > ((BN_ULONG)1 << BN_BITS4)) {
31 BIGNUM *tmp = BN_dup(a);
32 if (tmp == NULL)
33 return (BN_ULONG)-1;
34
35 ret = BN_div_word(tmp, w);
36 BN_free(tmp);
37
38 return ret;
39 }
40#endif
41
42 bn_check_top(a);
43 w &= BN_MASK2;
44 for (i = a->top - 1; i >= 0; i--) {
45#ifndef BN_LLONG
46 /*
47 * We can assume here that | w <= ((BN_ULONG)1 << BN_BITS4) | and so
48 * | ret < ((BN_ULONG)1 << BN_BITS4) | and therefore the shifts here are
49 * safe and will not overflow
50 */
51 ret = ((ret << BN_BITS4) | ((a->d[i] >> BN_BITS4) & BN_MASK2l)) % w;
52 ret = ((ret << BN_BITS4) | (a->d[i] & BN_MASK2l)) % w;
53#else
54 ret = (BN_ULLONG) (((ret << (BN_ULLONG) BN_BITS2) | a->d[i]) %
55 (BN_ULLONG) w);
56#endif
57 }
58 return (BN_ULONG)ret;
59}
60
61BN_ULONG BN_div_word(BIGNUM *a, BN_ULONG w)
62{
63 BN_ULONG ret = 0;
64 int i, j;
65
66 bn_check_top(a);
67 w &= BN_MASK2;
68
69 if (!w)
70 /* actually this an error (division by zero) */
71 return (BN_ULONG)-1;
72 if (a->top == 0)
73 return 0;
74
75 /* normalize input (so bn_div_words doesn't complain) */
76 j = BN_BITS2 - BN_num_bits_word(w);
77 w <<= j;
78 if (!BN_lshift(a, a, j))
79 return (BN_ULONG)-1;
80
81 for (i = a->top - 1; i >= 0; i--) {
82 BN_ULONG l, d;
83
84 l = a->d[i];
85 d = bn_div_words(ret, l, w);
86 ret = (l - ((d * w) & BN_MASK2)) & BN_MASK2;
87 a->d[i] = d;
88 }
89 if ((a->top > 0) && (a->d[a->top - 1] == 0))
90 a->top--;
91 ret >>= j;
92 if (!a->top)
93 a->neg = 0; /* don't allow negative zero */
94 bn_check_top(a);
95 return ret;
96}
97
98int BN_add_word(BIGNUM *a, BN_ULONG w)
99{
100 BN_ULONG l;
101 int i;
102
103 bn_check_top(a);
104 w &= BN_MASK2;
105
106 /* degenerate case: w is zero */
107 if (!w)
108 return 1;
109 /* degenerate case: a is zero */
110 if (BN_is_zero(a))
111 return BN_set_word(a, w);
112 /* handle 'a' when negative */
113 if (a->neg) {
114 a->neg = 0;
115 i = BN_sub_word(a, w);
116 if (!BN_is_zero(a))
117 a->neg = !(a->neg);
118 return i;
119 }
120 for (i = 0; w != 0 && i < a->top; i++) {
121 a->d[i] = l = (a->d[i] + w) & BN_MASK2;
122 w = (w > l) ? 1 : 0;
123 }
124 if (w && i == a->top) {
125 if (bn_wexpand(a, a->top + 1) == NULL)
126 return 0;
127 a->top++;
128 a->d[i] = w;
129 }
130 bn_check_top(a);
131 return 1;
132}
133
134int BN_sub_word(BIGNUM *a, BN_ULONG w)
135{
136 int i;
137
138 bn_check_top(a);
139 w &= BN_MASK2;
140
141 /* degenerate case: w is zero */
142 if (!w)
143 return 1;
144 /* degenerate case: a is zero */
145 if (BN_is_zero(a)) {
146 i = BN_set_word(a, w);
147 if (i != 0)
148 BN_set_negative(a, 1);
149 return i;
150 }
151 /* handle 'a' when negative */
152 if (a->neg) {
153 a->neg = 0;
154 i = BN_add_word(a, w);
155 a->neg = 1;
156 return i;
157 }
158
159 if ((a->top == 1) && (a->d[0] < w)) {
160 a->d[0] = w - a->d[0];
161 a->neg = 1;
162 return 1;
163 }
164 i = 0;
165 for (;;) {
166 if (a->d[i] >= w) {
167 a->d[i] -= w;
168 break;
169 } else {
170 a->d[i] = (a->d[i] - w) & BN_MASK2;
171 i++;
172 w = 1;
173 }
174 }
175 if ((a->d[i] == 0) && (i == (a->top - 1)))
176 a->top--;
177 bn_check_top(a);
178 return 1;
179}
180
181int BN_mul_word(BIGNUM *a, BN_ULONG w)
182{
183 BN_ULONG ll;
184
185 bn_check_top(a);
186 w &= BN_MASK2;
187 if (a->top) {
188 if (w == 0)
189 BN_zero(a);
190 else {
191 ll = bn_mul_words(a->d, a->d, a->top, w);
192 if (ll) {
193 if (bn_wexpand(a, a->top + 1) == NULL)
194 return 0;
195 a->d[a->top++] = ll;
196 }
197 }
198 }
199 bn_check_top(a);
200 return 1;
201}
202