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1 /* Bitfields
2 * Copyright (C) 2016 Cumulus Networks, Inc.
3 *
4 * This file is part of Quagga.
5 *
6 * Quagga is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License as published by the
8 * Free Software Foundation; either version 2, or (at your option) any
9 * later version.
10 *
11 * Quagga is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License along
17 * with this program; see the file COPYING; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
19 */
20 /**
21 * A simple bit array implementation to allocate and free IDs. An example
22 * of its usage is in allocating link state IDs for OSPFv3 as OSPFv3 has
23 * removed all address semantics from LS ID. Another usage can be in
24 * allocating IDs for BGP neighbors (and dynamic update groups) for
25 * efficient storage of adj-rib-out.
26 *
27 * An example:
28 * #include "bitfield.h"
29 *
30 * bitfield_t bitfield;
31 *
32 * bf_init(bitfield, 32);
33 * ...
34 * bf_assign_index(bitfield, id1);
35 * bf_assign_index(bitfield, id2);
36 * ...
37 * bf_release_index(bitfield, id1);
38 */
39
40 #ifndef _BITFIELD_H
41 #define _BITFIELD_H
42
43 #include <stdio.h>
44 #include <string.h>
45 #include <stdlib.h>
46
47 #ifdef __cplusplus
48 extern "C" {
49 #endif
50
51 typedef unsigned int word_t;
52 #define WORD_MAX 0xFFFFFFFF
53 #define WORD_SIZE (sizeof(word_t) * 8)
54
55 /**
56 * The bitfield structure.
57 * @data: the bits to manage.
58 * @n: The current word number that is being used.
59 * @m: total number of words in 'data'
60 */
61 typedef struct {word_t *data; size_t n, m; } bitfield_t;
62
63 DECLARE_MTYPE(BITFIELD);
64
65 /**
66 * Initialize the bits.
67 * @v: an instance of bitfield_t struct.
68 * @N: number of bits to start with, which equates to how many
69 * IDs can be allocated.
70 */
71 #define bf_init(v, N) \
72 do { \
73 (v).n = 0; \
74 (v).m = ((N) / WORD_SIZE + 1); \
75 (v).data = XCALLOC(MTYPE_BITFIELD, ((v).m * sizeof(word_t))); \
76 } while (0)
77
78 /**
79 * allocate and assign an id from bitfield v.
80 */
81 #define bf_assign_index(v, id) \
82 do { \
83 bf_find_bit(v, id); \
84 bf_set_bit(v, id); \
85 } while (0)
86
87 /*
88 * allocate and assign 0th bit in the bitfiled.
89 */
90 #define bf_assign_zero_index(v) \
91 do { \
92 int id = 0; \
93 bf_assign_index(v, id); \
94 } while (0)
95
96 /*
97 * return an id to bitfield v
98 */
99 #define bf_release_index(v, id) \
100 (v).data[bf_index(id)] &= ~(1 << (bf_offset(id)))
101
102 /* check if an id is in use */
103 #define bf_test_index(v, id) \
104 ((v).data[bf_index(id)] & (1 << (bf_offset(id))))
105
106 /* check if the bit field has been setup */
107 #define bf_is_inited(v) ((v).data)
108
109 /* compare two bitmaps of the same length */
110 #define bf_cmp(v1, v2) (memcmp((v1).data, (v2).data, ((v1).m * sizeof(word_t))))
111
112 /*
113 * return 0th index back to bitfield
114 */
115 #define bf_release_zero_index(v) bf_release_index(v, 0)
116
117 #define bf_index(b) ((b) / WORD_SIZE)
118 #define bf_offset(b) ((b) % WORD_SIZE)
119
120 /**
121 * Set a bit in the array. If it fills up that word and we are
122 * out of words, extend it by one more word.
123 */
124 #define bf_set_bit(v, b) \
125 do { \
126 size_t w = bf_index(b); \
127 (v).data[w] |= 1 << (bf_offset(b)); \
128 (v).n += ((v).data[w] == WORD_MAX); \
129 if ((v).n == (v).m) { \
130 (v).m = (v).m + 1; \
131 (v).data = realloc((v).data, (v).m * sizeof(word_t)); \
132 } \
133 } while (0)
134
135 /* Find a clear bit in v and assign it to b. */
136 #define bf_find_bit(v, b) \
137 do { \
138 word_t word = 0; \
139 unsigned int w, sh; \
140 for (w = 0; w <= (v).n; w++) { \
141 if ((word = (v).data[w]) != WORD_MAX) \
142 break; \
143 } \
144 (b) = ((word & 0xFFFF) == 0xFFFF) << 4; \
145 word >>= (b); \
146 sh = ((word & 0xFF) == 0xFF) << 3; \
147 word >>= sh; \
148 (b) |= sh; \
149 sh = ((word & 0xF) == 0xF) << 2; \
150 word >>= sh; \
151 (b) |= sh; \
152 sh = ((word & 0x3) == 0x3) << 1; \
153 word >>= sh; \
154 (b) |= sh; \
155 sh = ((word & 0x1) == 0x1) << 0; \
156 word >>= sh; \
157 (b) |= sh; \
158 (b) += (w * WORD_SIZE); \
159 } while (0)
160
161 /*
162 * Find a clear bit in v and return it
163 * Start looking in the word containing bit position start_index.
164 * If necessary, wrap around after bit position max_index.
165 */
166 static inline unsigned int
167 bf_find_next_clear_bit_wrap(bitfield_t *v, word_t start_index, word_t max_index)
168 {
169 int start_bit;
170 unsigned long i, offset, scanbits, wordcount_max, index_max;
171
172 if (start_index > max_index)
173 start_index = 0;
174
175 start_bit = start_index & (WORD_SIZE - 1);
176 wordcount_max = bf_index(max_index) + 1;
177
178 scanbits = WORD_SIZE;
179 for (i = bf_index(start_index); i < v->m; ++i) {
180 if (v->data[i] == WORD_MAX) {
181 /* if the whole word is full move to the next */
182 start_bit = 0;
183 continue;
184 }
185 /* scan one word for clear bits */
186 if ((i == v->m - 1) && (v->m >= wordcount_max))
187 /* max index could be only part of word */
188 scanbits = (max_index % WORD_SIZE) + 1;
189 for (offset = start_bit; offset < scanbits; ++offset) {
190 if (!((v->data[i] >> offset) & 1))
191 return ((i * WORD_SIZE) + offset);
192 }
193 /* move to the next word */
194 start_bit = 0;
195 }
196
197 if (v->m < wordcount_max) {
198 /*
199 * We can expand bitfield, so no need to wrap.
200 * Return the index of the first bit of the next word.
201 * Assumption is that caller will call bf_set_bit which
202 * will allocate additional space.
203 */
204 v->m += 1;
205 v->data = (word_t *)realloc(v->data, v->m * sizeof(word_t));
206 v->data[v->m - 1] = 0;
207 return v->m * WORD_SIZE;
208 }
209
210 /*
211 * start looking for a clear bit at the start of the bitfield and
212 * stop when we reach start_index
213 */
214 scanbits = WORD_SIZE;
215 index_max = bf_index(start_index - 1);
216 for (i = 0; i <= index_max; ++i) {
217 if (i == index_max)
218 scanbits = ((start_index - 1) % WORD_SIZE) + 1;
219 for (offset = start_bit; offset < scanbits; ++offset) {
220 if (!((v->data[i] >> offset) & 1))
221 return ((i * WORD_SIZE) + offset);
222 }
223 /* move to the next word */
224 start_bit = 0;
225 }
226
227 return WORD_MAX;
228 }
229
230 static inline unsigned int bf_find_next_set_bit(bitfield_t v,
231 word_t start_index)
232 {
233 int start_bit;
234 unsigned long i, offset;
235
236 start_bit = start_index & (WORD_SIZE - 1);
237
238 for (i = bf_index(start_index); i < v.m; ++i) {
239 if (v.data[i] == 0) {
240 /* if the whole word is empty move to the next */
241 start_bit = 0;
242 continue;
243 }
244 /* scan one word for set bits */
245 for (offset = start_bit; offset < WORD_SIZE; ++offset) {
246 if ((v.data[i] >> offset) & 1)
247 return ((i * WORD_SIZE) + offset);
248 }
249 /* move to the next word */
250 start_bit = 0;
251 }
252 return WORD_MAX;
253 }
254
255 /* iterate through all the set bits */
256 #define bf_for_each_set_bit(v, b, max) \
257 for ((b) = bf_find_next_set_bit((v), 0); \
258 (b) < max; \
259 (b) = bf_find_next_set_bit((v), (b) + 1))
260
261 /*
262 * Free the allocated memory for data
263 * @v: an instance of bitfield_t struct.
264 */
265 #define bf_free(v) \
266 do { \
267 XFREE(MTYPE_BITFIELD, (v).data); \
268 (v).data = NULL; \
269 } while (0)
270
271 #ifdef __cplusplus
272 }
273 #endif
274
275 #endif