1 /* mpi-bit.c - MPI bit level fucntions
2 * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
3 *
4 * This file is part of GnuPG.
5 *
6 * GnuPG is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * GnuPG is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
19 */
20
21 #include "mpi-internal.h"
22 #include "longlong.h"
23
24 #define A_LIMB_1 ((mpi_limb_t) 1)
25
26 /****************
27 * Sometimes we have MSL (most significant limbs) which are 0;
28 * this is for some reasons not good, so this function removes them.
29 */
mpi_normalize(MPI a)30 void mpi_normalize(MPI a)
31 {
32 for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
33 ;
34 }
35
36 /****************
37 * Return the number of bits in A.
38 */
mpi_get_nbits(MPI a)39 unsigned mpi_get_nbits(MPI a)
40 {
41 unsigned n;
42
43 mpi_normalize(a);
44
45 if (a->nlimbs) {
46 mpi_limb_t alimb = a->d[a->nlimbs - 1];
47 if (alimb)
48 count_leading_zeros(n, alimb);
49 else
50 n = BITS_PER_MPI_LIMB;
51 n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
52 } else
53 n = 0;
54 return n;
55 }
56 EXPORT_SYMBOL_GPL(mpi_get_nbits);
57
58 /****************
59 * Test whether bit N is set.
60 */
mpi_test_bit(MPI a,unsigned n)61 int mpi_test_bit(MPI a, unsigned n)
62 {
63 unsigned limbno, bitno;
64 mpi_limb_t limb;
65
66 limbno = n / BITS_PER_MPI_LIMB;
67 bitno = n % BITS_PER_MPI_LIMB;
68
69 if (limbno >= a->nlimbs)
70 return 0; /* too far left: this is a 0 */
71 limb = a->d[limbno];
72 return (limb & (A_LIMB_1 << bitno)) ? 1 : 0;
73 }
74
75 /****************
76 * Set bit N of A.
77 */
mpi_set_bit(MPI a,unsigned n)78 int mpi_set_bit(MPI a, unsigned n)
79 {
80 unsigned limbno, bitno;
81
82 limbno = n / BITS_PER_MPI_LIMB;
83 bitno = n % BITS_PER_MPI_LIMB;
84
85 if (limbno >= a->nlimbs) { /* resize */
86 if (a->alloced >= limbno)
87 if (mpi_resize(a, limbno + 1) < 0)
88 return -ENOMEM;
89 a->nlimbs = limbno + 1;
90 }
91 a->d[limbno] |= (A_LIMB_1 << bitno);
92 return 0;
93 }
94
95 /****************
96 * Set bit N of A. and clear all bits above
97 */
mpi_set_highbit(MPI a,unsigned n)98 int mpi_set_highbit(MPI a, unsigned n)
99 {
100 unsigned limbno, bitno;
101
102 limbno = n / BITS_PER_MPI_LIMB;
103 bitno = n % BITS_PER_MPI_LIMB;
104
105 if (limbno >= a->nlimbs) { /* resize */
106 if (a->alloced >= limbno)
107 if (mpi_resize(a, limbno + 1) < 0)
108 return -ENOMEM;
109 a->nlimbs = limbno + 1;
110 }
111 a->d[limbno] |= (A_LIMB_1 << bitno);
112 for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++)
113 a->d[limbno] &= ~(A_LIMB_1 << bitno);
114 a->nlimbs = limbno + 1;
115 return 0;
116 }
117
118 /****************
119 * clear bit N of A and all bits above
120 */
mpi_clear_highbit(MPI a,unsigned n)121 void mpi_clear_highbit(MPI a, unsigned n)
122 {
123 unsigned limbno, bitno;
124
125 limbno = n / BITS_PER_MPI_LIMB;
126 bitno = n % BITS_PER_MPI_LIMB;
127
128 if (limbno >= a->nlimbs)
129 return; /* not allocated, so need to clear bits :-) */
130
131 for (; bitno < BITS_PER_MPI_LIMB; bitno++)
132 a->d[limbno] &= ~(A_LIMB_1 << bitno);
133 a->nlimbs = limbno + 1;
134 }
135
136 /****************
137 * Clear bit N of A.
138 */
mpi_clear_bit(MPI a,unsigned n)139 void mpi_clear_bit(MPI a, unsigned n)
140 {
141 unsigned limbno, bitno;
142
143 limbno = n / BITS_PER_MPI_LIMB;
144 bitno = n % BITS_PER_MPI_LIMB;
145
146 if (limbno >= a->nlimbs)
147 return; /* don't need to clear this bit, it's to far to left */
148 a->d[limbno] &= ~(A_LIMB_1 << bitno);
149 }
150
151 /****************
152 * Shift A by N bits to the right
153 * FIXME: should use alloc_limb if X and A are same.
154 */
mpi_rshift(MPI x,MPI a,unsigned n)155 int mpi_rshift(MPI x, MPI a, unsigned n)
156 {
157 mpi_ptr_t xp;
158 mpi_size_t xsize;
159
160 xsize = a->nlimbs;
161 x->sign = a->sign;
162 if (RESIZE_IF_NEEDED(x, (size_t) xsize) < 0)
163 return -ENOMEM;
164 xp = x->d;
165
166 if (xsize) {
167 mpihelp_rshift(xp, a->d, xsize, n);
168 MPN_NORMALIZE(xp, xsize);
169 }
170 x->nlimbs = xsize;
171 return 0;
172 }
173
174 /****************
175 * Shift A by COUNT limbs to the left
176 * This is used only within the MPI library
177 */
mpi_lshift_limbs(MPI a,unsigned int count)178 int mpi_lshift_limbs(MPI a, unsigned int count)
179 {
180 mpi_ptr_t ap = a->d;
181 int n = a->nlimbs;
182 int i;
183
184 if (!count || !n)
185 return 0;
186
187 if (RESIZE_IF_NEEDED(a, n + count) < 0)
188 return -ENOMEM;
189
190 for (i = n - 1; i >= 0; i--)
191 ap[i + count] = ap[i];
192 for (i = 0; i < count; i++)
193 ap[i] = 0;
194 a->nlimbs += count;
195 return 0;
196 }
197
198 /****************
199 * Shift A by COUNT limbs to the right
200 * This is used only within the MPI library
201 */
mpi_rshift_limbs(MPI a,unsigned int count)202 void mpi_rshift_limbs(MPI a, unsigned int count)
203 {
204 mpi_ptr_t ap = a->d;
205 mpi_size_t n = a->nlimbs;
206 unsigned int i;
207
208 if (count >= n) {
209 a->nlimbs = 0;
210 return;
211 }
212
213 for (i = 0; i < n - count; i++)
214 ap[i] = ap[i + count];
215 ap[i] = 0;
216 a->nlimbs -= count;
217 }
218