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1/* mpi-bit.c - MPI bit level functions
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 <linux/export.h>
22
23#include "mpi-internal.h"
24#include "longlong.h"
25
26#define A_LIMB_1 ((mpi_limb_t) 1)
27
28/****************
29 * Sometimes we have MSL (most significant limbs) which are 0;
30 * this is for some reasons not good, so this function removes them.
31 */
32void mpi_normalize(MPI a)
33{
34 for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
35 ;
36}
37
38/****************
39 * Return the number of bits in A.
40 */
41unsigned mpi_get_nbits(MPI a)
42{
43 unsigned n;
44
45 mpi_normalize(a);
46
47 if (a->nlimbs) {
48 mpi_limb_t alimb = a->d[a->nlimbs - 1];
49 if (alimb)
50 n = count_leading_zeros(alimb);
51 else
52 n = BITS_PER_MPI_LIMB;
53 n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
54 } else
55 n = 0;
56 return n;
57}
58EXPORT_SYMBOL_GPL(mpi_get_nbits);
59
60/****************
61 * Test whether bit N is set.
62 */
63int mpi_test_bit(MPI a, unsigned int n)
64{
65 unsigned int limbno, bitno;
66 mpi_limb_t limb;
67
68 limbno = n / BITS_PER_MPI_LIMB;
69 bitno = n % BITS_PER_MPI_LIMB;
70
71 if (limbno >= a->nlimbs)
72 return 0; /* too far left: this is a 0 */
73 limb = a->d[limbno];
74 return (limb & (A_LIMB_1 << bitno)) ? 1 : 0;
75}
76EXPORT_SYMBOL_GPL(mpi_test_bit);
77
78/****************
79 * Set bit N of A.
80 */
81int mpi_set_bit(MPI a, unsigned int n)
82{
83 unsigned int i, limbno, bitno;
84 int err;
85
86 limbno = n / BITS_PER_MPI_LIMB;
87 bitno = n % BITS_PER_MPI_LIMB;
88
89 if (limbno >= a->nlimbs) {
90 for (i = a->nlimbs; i < a->alloced; i++)
91 a->d[i] = 0;
92 err = mpi_resize(a, limbno+1);
93 if (err)
94 return err;
95 a->nlimbs = limbno+1;
96 }
97 a->d[limbno] |= (A_LIMB_1<<bitno);
98 return 0;
99}
100EXPORT_SYMBOL_GPL(mpi_set_bit);
101
102/*
103 * Shift A by N bits to the right.
104 */
105int mpi_rshift(MPI x, MPI a, unsigned int n)
106{
107 mpi_size_t xsize;
108 unsigned int i;
109 unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
110 unsigned int nbits = (n%BITS_PER_MPI_LIMB);
111 int err;
112
113 if (x == a) {
114 /* In-place operation. */
115 if (nlimbs >= x->nlimbs) {
116 x->nlimbs = 0;
117 return 0;
118 }
119
120 if (nlimbs) {
121 for (i = 0; i < x->nlimbs - nlimbs; i++)
122 x->d[i] = x->d[i+nlimbs];
123 x->d[i] = 0;
124 x->nlimbs -= nlimbs;
125 }
126 if (x->nlimbs && nbits)
127 mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
128 } else if (nlimbs) {
129 /* Copy and shift by more or equal bits than in a limb. */
130 xsize = a->nlimbs;
131 x->sign = a->sign;
132 err = RESIZE_IF_NEEDED(x, xsize);
133 if (err)
134 return err;
135 x->nlimbs = xsize;
136 for (i = 0; i < a->nlimbs; i++)
137 x->d[i] = a->d[i];
138 x->nlimbs = i;
139
140 if (nlimbs >= x->nlimbs) {
141 x->nlimbs = 0;
142 return 0;
143 }
144
145 for (i = 0; i < x->nlimbs - nlimbs; i++)
146 x->d[i] = x->d[i+nlimbs];
147 x->d[i] = 0;
148 x->nlimbs -= nlimbs;
149
150 if (x->nlimbs && nbits)
151 mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
152 } else {
153 /* Copy and shift by less than bits in a limb. */
154 xsize = a->nlimbs;
155 x->sign = a->sign;
156 err = RESIZE_IF_NEEDED(x, xsize);
157 if (err)
158 return err;
159 x->nlimbs = xsize;
160
161 if (xsize) {
162 if (nbits)
163 mpihelp_rshift(x->d, a->d, x->nlimbs, nbits);
164 else {
165 /* The rshift helper function is not specified for
166 * NBITS==0, thus we do a plain copy here.
167 */
168 for (i = 0; i < x->nlimbs; i++)
169 x->d[i] = a->d[i];
170 }
171 }
172 }
173 MPN_NORMALIZE(x->d, x->nlimbs);
174
175 return 0;
176}
177EXPORT_SYMBOL_GPL(mpi_rshift);