lib/bitfield.h

   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 static inline unsigned int bf_find_next_set_bit(bitfield_t v,
 162                 word_t start_index)
 163 {
 164         int start_bit;
 165         unsigned long i, offset;
 166
 167         start_bit = start_index & (WORD_SIZE - 1);
 168
 169         for (i = bf_index(start_index); i < v.m; ++i) {
 170                 if (v.data[i] == 0) {
 171                         /* if the whole word is empty move to the next */
 172                         start_bit = 0;
 173                         continue;
 174                 }
 175                 /* scan one word for set bits */
 176                 for (offset = start_bit; offset < WORD_SIZE; ++offset) {
 177                         if ((v.data[i] >> offset) & 1)
 178                                 return ((i * WORD_SIZE) + offset);
 179                 }
 180                 /* move to the next word */
 181                 start_bit = 0;
 182         }
 183         return WORD_MAX;
 184 }
 185
 186 /* iterate through all the set bits */
 187 #define bf_for_each_set_bit(v, b, max)                 \
 188         for ((b) = bf_find_next_set_bit((v), 0);           \
 189                         (b) < max;                                 \
 190                         (b) = bf_find_next_set_bit((v), (b) + 1))
 191
 192 /*
 193  * Free the allocated memory for data
 194  * @v: an instance of bitfield_t struct.
 195  */
 196 #define bf_free(v)                                                             \
 197         do {                                                                   \
 198                 XFREE(MTYPE_BITFIELD, (v).data);                               \
 199                 (v).data = NULL;                                               \
 200         } while (0)
 201
 202 #ifdef __cplusplus
 203 }
 204 #endif
 205
 206 #endif