bn_word.c revision 306195 
1/* crypto/bn/bn_word.c */
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#include "cryptlib.h"
61#include "bn_lcl.h"
62
63BN_ULONG BN_mod_word(const BIGNUM *a, BN_ULONG w)
64{
65#ifndef BN_LLONG
66    BN_ULONG ret = 0;
67#else
68    BN_ULLONG ret = 0;
69#endif
70    int i;
71
72    if (w == 0)
73        return (BN_ULONG)-1;
74
75#ifndef BN_LLONG
76    /*
77     * If |w| is too long and we don't have BN_ULLONG then we need to fall
78     * back to using BN_div_word
79     */
80    if (w > ((BN_ULONG)1 << BN_BITS4)) {
81        BIGNUM *tmp = BN_dup(a);
82        if (tmp == NULL)
83            return (BN_ULONG)-1;
84
85        ret = BN_div_word(tmp, w);
86        BN_free(tmp);
87
88        return ret;
89    }
90#endif
91
92    bn_check_top(a);
93    w &= BN_MASK2;
94    for (i = a->top - 1; i >= 0; i--) {
95#ifndef BN_LLONG
96        /*
97         * We can assume here that | w <= ((BN_ULONG)1 << BN_BITS4) | and so
98         * | ret < ((BN_ULONG)1 << BN_BITS4) | and therefore the shifts here are
99         * safe and will not overflow
100         */
101        ret = ((ret << BN_BITS4) | ((a->d[i] >> BN_BITS4) & BN_MASK2l)) % w;
102        ret = ((ret << BN_BITS4) | (a->d[i] & BN_MASK2l)) % w;
103#else
104        ret = (BN_ULLONG) (((ret << (BN_ULLONG) BN_BITS2) | a->d[i]) %
105                           (BN_ULLONG) w);
106#endif
107    }
108    return ((BN_ULONG)ret);
109}
110
111BN_ULONG BN_div_word(BIGNUM *a, BN_ULONG w)
112{
113    BN_ULONG ret = 0;
114    int i, j;
115
116    bn_check_top(a);
117    w &= BN_MASK2;
118
119    if (!w)
120        /* actually this an error (division by zero) */
121        return (BN_ULONG)-1;
122    if (a->top == 0)
123        return 0;
124
125    /* normalize input (so bn_div_words doesn't complain) */
126    j = BN_BITS2 - BN_num_bits_word(w);
127    w <<= j;
128    if (!BN_lshift(a, a, j))
129        return (BN_ULONG)-1;
130
131    for (i = a->top - 1; i >= 0; i--) {
132        BN_ULONG l, d;
133
134        l = a->d[i];
135        d = bn_div_words(ret, l, w);
136        ret = (l - ((d * w) & BN_MASK2)) & BN_MASK2;
137        a->d[i] = d;
138    }
139    if ((a->top > 0) && (a->d[a->top - 1] == 0))
140        a->top--;
141    ret >>= j;
142    bn_check_top(a);
143    return (ret);
144}
145
146int BN_add_word(BIGNUM *a, BN_ULONG w)
147{
148    BN_ULONG l;
149    int i;
150
151    bn_check_top(a);
152    w &= BN_MASK2;
153
154    /* degenerate case: w is zero */
155    if (!w)
156        return 1;
157    /* degenerate case: a is zero */
158    if (BN_is_zero(a))
159        return BN_set_word(a, w);
160    /* handle 'a' when negative */
161    if (a->neg) {
162        a->neg = 0;
163        i = BN_sub_word(a, w);
164        if (!BN_is_zero(a))
165            a->neg = !(a->neg);
166        return (i);
167    }
168    for (i = 0; w != 0 && i < a->top; i++) {
169        a->d[i] = l = (a->d[i] + w) & BN_MASK2;
170        w = (w > l) ? 1 : 0;
171    }
172    if (w && i == a->top) {
173        if (bn_wexpand(a, a->top + 1) == NULL)
174            return 0;
175        a->top++;
176        a->d[i] = w;
177    }
178    bn_check_top(a);
179    return (1);
180}
181
182int BN_sub_word(BIGNUM *a, BN_ULONG w)
183{
184    int i;
185
186    bn_check_top(a);
187    w &= BN_MASK2;
188
189    /* degenerate case: w is zero */
190    if (!w)
191        return 1;
192    /* degenerate case: a is zero */
193    if (BN_is_zero(a)) {
194        i = BN_set_word(a, w);
195        if (i != 0)
196            BN_set_negative(a, 1);
197        return i;
198    }
199    /* handle 'a' when negative */
200    if (a->neg) {
201        a->neg = 0;
202        i = BN_add_word(a, w);
203        a->neg = 1;
204        return (i);
205    }
206
207    if ((a->top == 1) && (a->d[0] < w)) {
208        a->d[0] = w - a->d[0];
209        a->neg = 1;
210        return (1);
211    }
212    i = 0;
213    for (;;) {
214        if (a->d[i] >= w) {
215            a->d[i] -= w;
216            break;
217        } else {
218            a->d[i] = (a->d[i] - w) & BN_MASK2;
219            i++;
220            w = 1;
221        }
222    }
223    if ((a->d[i] == 0) && (i == (a->top - 1)))
224        a->top--;
225    bn_check_top(a);
226    return (1);
227}
228
229int BN_mul_word(BIGNUM *a, BN_ULONG w)
230{
231    BN_ULONG ll;
232
233    bn_check_top(a);
234    w &= BN_MASK2;
235    if (a->top) {
236        if (w == 0)
237            BN_zero(a);
238        else {
239            ll = bn_mul_words(a->d, a->d, a->top, w);
240            if (ll) {
241                if (bn_wexpand(a, a->top + 1) == NULL)
242                    return (0);
243                a->d[a->top++] = ll;
244            }
245        }
246    }
247    bn_check_top(a);
248    return (1);
249}
250