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 "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 */
30 void mpi_normalize(MPI a)
31 {
32 for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
33 ;
34 }
35 EXPORT_SYMBOL_GPL(mpi_normalize);
36
37 /****************
38 * Return the number of bits in A.
39 */
40 unsigned mpi_get_nbits(MPI a)
41 {
42 unsigned n;
43
44 mpi_normalize(a);
45
46 if (a->nlimbs) {
47 mpi_limb_t alimb = a->d[a->nlimbs - 1];
48 if (alimb)
49 n = count_leading_zeros(alimb);
50 else
51 n = BITS_PER_MPI_LIMB;
52 n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
53 } else
54 n = 0;
55 return n;
56 }
57 EXPORT_SYMBOL_GPL(mpi_get_nbits);
58
59 /****************
60 * Test whether bit N is set.
61 */
62 int mpi_test_bit(MPI a, unsigned int n)
63 {
64 unsigned int limbno, bitno;
65 mpi_limb_t limb;
66
67 limbno = n / BITS_PER_MPI_LIMB;
68 bitno = n % BITS_PER_MPI_LIMB;
69
70 if (limbno >= a->nlimbs)
71 return 0; /* too far left: this is a 0 */
72 limb = a->d[limbno];
73 return (limb & (A_LIMB_1 << bitno)) ? 1 : 0;
74 }
75 EXPORT_SYMBOL_GPL(mpi_test_bit);
76
77 /****************
78 * Set bit N of A.
79 */
80 void mpi_set_bit(MPI a, unsigned int n)
81 {
82 unsigned int i, limbno, bitno;
83
84 limbno = n / BITS_PER_MPI_LIMB;
85 bitno = n % BITS_PER_MPI_LIMB;
86
87 if (limbno >= a->nlimbs) {
88 for (i = a->nlimbs; i < a->alloced; i++)
89 a->d[i] = 0;
90 mpi_resize(a, limbno+1);
91 a->nlimbs = limbno+1;
92 }
93 a->d[limbno] |= (A_LIMB_1<<bitno);
94 }
95
96 /****************
97 * Set bit N of A. and clear all bits above
98 */
99 void mpi_set_highbit(MPI a, unsigned int n)
100 {
101 unsigned int i, limbno, bitno;
102
103 limbno = n / BITS_PER_MPI_LIMB;
104 bitno = n % BITS_PER_MPI_LIMB;
105
106 if (limbno >= a->nlimbs) {
107 for (i = a->nlimbs; i < a->alloced; i++)
108 a->d[i] = 0;
109 mpi_resize(a, limbno+1);
110 a->nlimbs = limbno+1;
111 }
112 a->d[limbno] |= (A_LIMB_1<<bitno);
113 for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++)
114 a->d[limbno] &= ~(A_LIMB_1 << bitno);
115 a->nlimbs = limbno+1;
116 }
117 EXPORT_SYMBOL_GPL(mpi_set_highbit);
118
119 /****************
120 * clear bit N of A and all bits above
121 */
122 void mpi_clear_highbit(MPI a, unsigned int n)
123 {
124 unsigned int limbno, bitno;
125
126 limbno = n / BITS_PER_MPI_LIMB;
127 bitno = n % BITS_PER_MPI_LIMB;
128
129 if (limbno >= a->nlimbs)
130 return; /* not allocated, therefore no need to clear bits :-) */
131
132 for ( ; bitno < BITS_PER_MPI_LIMB; bitno++)
133 a->d[limbno] &= ~(A_LIMB_1 << bitno);
134 a->nlimbs = limbno+1;
135 }
136
137 /****************
138 * Clear bit N of A.
139 */
140 void mpi_clear_bit(MPI a, unsigned int n)
141 {
142 unsigned int limbno, bitno;
143
144 limbno = n / BITS_PER_MPI_LIMB;
145 bitno = n % BITS_PER_MPI_LIMB;
146
147 if (limbno >= a->nlimbs)
148 return; /* Don't need to clear this bit, it's far too left. */
149 a->d[limbno] &= ~(A_LIMB_1 << bitno);
150 }
151 EXPORT_SYMBOL_GPL(mpi_clear_bit);
152
153
154 /****************
155 * Shift A by COUNT limbs to the right
156 * This is used only within the MPI library
157 */
158 void mpi_rshift_limbs(MPI a, unsigned int count)
159 {
160 mpi_ptr_t ap = a->d;
161 mpi_size_t n = a->nlimbs;
162 unsigned int i;
163
164 if (count >= n) {
165 a->nlimbs = 0;
166 return;
167 }
168
169 for (i = 0; i < n - count; i++)
170 ap[i] = ap[i+count];
171 ap[i] = 0;
172 a->nlimbs -= count;
173 }
174
175 /*
176 * Shift A by N bits to the right.
177 */
178 void mpi_rshift(MPI x, MPI a, unsigned int n)
179 {
180 mpi_size_t xsize;
181 unsigned int i;
182 unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
183 unsigned int nbits = (n%BITS_PER_MPI_LIMB);
184
185 if (x == a) {
186 /* In-place operation. */
187 if (nlimbs >= x->nlimbs) {
188 x->nlimbs = 0;
189 return;
190 }
191
192 if (nlimbs) {
193 for (i = 0; i < x->nlimbs - nlimbs; i++)
194 x->d[i] = x->d[i+nlimbs];
195 x->d[i] = 0;
196 x->nlimbs -= nlimbs;
197 }
198 if (x->nlimbs && nbits)
199 mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
200 } else if (nlimbs) {
201 /* Copy and shift by more or equal bits than in a limb. */
202 xsize = a->nlimbs;
203 x->sign = a->sign;
204 RESIZE_IF_NEEDED(x, xsize);
205 x->nlimbs = xsize;
206 for (i = 0; i < a->nlimbs; i++)
207 x->d[i] = a->d[i];
208 x->nlimbs = i;
209
210 if (nlimbs >= x->nlimbs) {
211 x->nlimbs = 0;
212 return;
213 }
214
215 for (i = 0; i < x->nlimbs - nlimbs; i++)
216 x->d[i] = x->d[i+nlimbs];
217 x->d[i] = 0;
218 x->nlimbs -= nlimbs;
219
220 if (x->nlimbs && nbits)
221 mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
222 } else {
223 /* Copy and shift by less than bits in a limb. */
224 xsize = a->nlimbs;
225 x->sign = a->sign;
226 RESIZE_IF_NEEDED(x, xsize);
227 x->nlimbs = xsize;
228
229 if (xsize) {
230 if (nbits)
231 mpihelp_rshift(x->d, a->d, x->nlimbs, nbits);
232 else {
233 /* The rshift helper function is not specified for
234 * NBITS==0, thus we do a plain copy here.
235 */
236 for (i = 0; i < x->nlimbs; i++)
237 x->d[i] = a->d[i];
238 }
239 }
240 }
241 MPN_NORMALIZE(x->d, x->nlimbs);
242 }
243 EXPORT_SYMBOL_GPL(mpi_rshift);
244
245 /****************
246 * Shift A by COUNT limbs to the left
247 * This is used only within the MPI library
248 */
249 void mpi_lshift_limbs(MPI a, unsigned int count)
250 {
251 mpi_ptr_t ap;
252 int n = a->nlimbs;
253 int i;
254
255 if (!count || !n)
256 return;
257
258 RESIZE_IF_NEEDED(a, n+count);
259
260 ap = a->d;
261 for (i = n-1; i >= 0; i--)
262 ap[i+count] = ap[i];
263 for (i = 0; i < count; i++)
264 ap[i] = 0;
265 a->nlimbs += count;
266 }
267
268 /*
269 * Shift A by N bits to the left.
270 */
271 void mpi_lshift(MPI x, MPI a, unsigned int n)
272 {
273 unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
274 unsigned int nbits = (n%BITS_PER_MPI_LIMB);
275
276 if (x == a && !n)
277 return; /* In-place shift with an amount of zero. */
278
279 if (x != a) {
280 /* Copy A to X. */
281 unsigned int alimbs = a->nlimbs;
282 int asign = a->sign;
283 mpi_ptr_t xp, ap;
284
285 RESIZE_IF_NEEDED(x, alimbs+nlimbs+1);
286 xp = x->d;
287 ap = a->d;
288 MPN_COPY(xp, ap, alimbs);
289 x->nlimbs = alimbs;
290 x->flags = a->flags;
291 x->sign = asign;
292 }
293
294 if (nlimbs && !nbits) {
295 /* Shift a full number of limbs. */
296 mpi_lshift_limbs(x, nlimbs);
297 } else if (n) {
298 /* We use a very dump approach: Shift left by the number of
299 * limbs plus one and than fix it up by an rshift.
300 */
301 mpi_lshift_limbs(x, nlimbs+1);
302 mpi_rshift(x, x, BITS_PER_MPI_LIMB - nbits);
303 }
304
305 MPN_NORMALIZE(x->d, x->nlimbs);
306 }
307
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