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(x: 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, nlimbs: 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, nlimbs: 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(wp: x->d, up: x->d, usize: x->nlimbs, cnt: 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 | if (nlimbs) { |
216 | for (i = 0; i < x->nlimbs - nlimbs; i++) |
217 | x->d[i] = x->d[i+nlimbs]; |
218 | x->d[i] = 0; |
219 | x->nlimbs -= nlimbs; |
220 | } |
221 | |
222 | if (x->nlimbs && nbits) |
223 | mpihelp_rshift(wp: x->d, up: x->d, usize: x->nlimbs, cnt: nbits); |
224 | } else { |
225 | /* Copy and shift by less than bits in a limb. */ |
226 | xsize = a->nlimbs; |
227 | x->sign = a->sign; |
228 | RESIZE_IF_NEEDED(x, xsize); |
229 | x->nlimbs = xsize; |
230 | |
231 | if (xsize) { |
232 | if (nbits) |
233 | mpihelp_rshift(wp: x->d, up: a->d, usize: x->nlimbs, cnt: nbits); |
234 | else { |
235 | /* The rshift helper function is not specified for |
236 | * NBITS==0, thus we do a plain copy here. |
237 | */ |
238 | for (i = 0; i < x->nlimbs; i++) |
239 | x->d[i] = a->d[i]; |
240 | } |
241 | } |
242 | } |
243 | MPN_NORMALIZE(x->d, x->nlimbs); |
244 | } |
245 | EXPORT_SYMBOL_GPL(mpi_rshift); |
246 | |
247 | /**************** |
248 | * Shift A by COUNT limbs to the left |
249 | * This is used only within the MPI library |
250 | */ |
251 | void mpi_lshift_limbs(MPI a, unsigned int count) |
252 | { |
253 | mpi_ptr_t ap; |
254 | int n = a->nlimbs; |
255 | int i; |
256 | |
257 | if (!count || !n) |
258 | return; |
259 | |
260 | RESIZE_IF_NEEDED(a, n+count); |
261 | |
262 | ap = a->d; |
263 | for (i = n-1; i >= 0; i--) |
264 | ap[i+count] = ap[i]; |
265 | for (i = 0; i < count; i++) |
266 | ap[i] = 0; |
267 | a->nlimbs += count; |
268 | } |
269 | |
270 | /* |
271 | * Shift A by N bits to the left. |
272 | */ |
273 | void mpi_lshift(MPI x, MPI a, unsigned int n) |
274 | { |
275 | unsigned int nlimbs = (n/BITS_PER_MPI_LIMB); |
276 | unsigned int nbits = (n%BITS_PER_MPI_LIMB); |
277 | |
278 | if (x == a && !n) |
279 | return; /* In-place shift with an amount of zero. */ |
280 | |
281 | if (x != a) { |
282 | /* Copy A to X. */ |
283 | unsigned int alimbs = a->nlimbs; |
284 | int asign = a->sign; |
285 | mpi_ptr_t xp, ap; |
286 | |
287 | RESIZE_IF_NEEDED(x, alimbs+nlimbs+1); |
288 | xp = x->d; |
289 | ap = a->d; |
290 | MPN_COPY(xp, ap, alimbs); |
291 | x->nlimbs = alimbs; |
292 | x->flags = a->flags; |
293 | x->sign = asign; |
294 | } |
295 | |
296 | if (nlimbs && !nbits) { |
297 | /* Shift a full number of limbs. */ |
298 | mpi_lshift_limbs(a: x, count: nlimbs); |
299 | } else if (n) { |
300 | /* We use a very dump approach: Shift left by the number of |
301 | * limbs plus one and than fix it up by an rshift. |
302 | */ |
303 | mpi_lshift_limbs(a: x, count: nlimbs+1); |
304 | mpi_rshift(x, x, BITS_PER_MPI_LIMB - nbits); |
305 | } |
306 | |
307 | MPN_NORMALIZE(x->d, x->nlimbs); |
308 | } |
309 | |