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 typedef unsigned int word_t;
  48 #define WORD_MAX 0xFFFFFFFF
  49 #define WORD_SIZE (sizeof(word_t) * 8)
  50
  51 /**
  52  * The bitfield structure.
  53  * @data: the bits to manage.
  54  * @n: The current word number that is being used.
  55  * @m: total number of words in 'data'
  56  */
  57 #define bitfield_t struct { word_t *data; size_t n, m; }
  58
  59 /**
  60  * Initialize the bits.
  61  * @v: an instance of bitfield_t struct.
  62  * @N: number of bits to start with, which equates to how many
  63  *     IDs can be allocated.
  64  */
  65 #define bf_init(v, N)                               \
  66   do {                                              \
  67     (v).n = 0;                                      \
  68     (v).m = ((N) / WORD_SIZE + 1);                  \
  69     (v).data = calloc(1, ((v).m * sizeof(word_t))); \
  70   } while (0)
  71
  72 /**
  73  * allocate and assign an id from bitfield v.
  74  */
  75 #define bf_assign_index(v, id)                          \
  76   do {                                                  \
  77     bf_find_bit(v, id);                                 \
  78     bf_set_bit(v, id);                                  \
  79   } while (0)
  80
  81 /**
  82  * return an id to bitfield v
  83  */
  84 #define bf_release_index(v, id)                 \
  85   (v).data[bf_index(id)] &= ~(1 << (bf_offset(id)))
  86
  87 #define bf_index(b) ((b) / WORD_SIZE)
  88 #define bf_offset(b) ((b) % WORD_SIZE)
  89
  90 /**
  91  * Set a bit in the array. If it fills up that word and we are
  92  * out of words, extend it by one more word.
  93  */
  94 #define bf_set_bit(v, b)                                        \
  95   do {                                                          \
  96     size_t w = bf_index(b);                                     \
  97     (v).data[w] |= 1 << (bf_offset(b));                         \
  98     (v).n += ((v).data[w] == WORD_MAX);                         \
  99     if ((v).n == (v).m) {                                       \
 100       (v).m = (v).m + 1;                                        \
 101       (v).data = realloc((v).data, (v).m * sizeof(word_t));     \
 102     }                                                           \
 103   } while (0)
 104
 105 /* Find a clear bit in v and assign it to b. */
 106 #define bf_find_bit(v, b)                                       \
 107   do {                                                          \
 108     word_t word = 0;                                            \
 109     unsigned int w, sh;                                         \
 110     for (w = 0; w <= (v).n; w++) {                              \
 111       if ((word = (v).data[w]) != WORD_MAX) break;              \
 112     }                                                           \
 113     (b) = ((word & 0xFFFF) == 0xFFFF) << 4; word >>= (b);       \
 114     sh = ((word & 0xFF) == 0xFF) << 3; word >>= sh; (b) |= sh;  \
 115     sh = ((word & 0xF) == 0xF) << 2; word >>= sh; (b) |= sh;    \
 116     sh = ((word & 0x3) == 0x3) << 1; word >>= sh; (b) |= sh;    \
 117     sh = ((word & 0x1) == 0x1) << 0; word >>= sh; (b) |= sh;    \
 118     (b) += (w * WORD_SIZE);                                     \
 119   } while (0)
 120
 121 #endif