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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 |