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